Download presentation
Presentation is loading. Please wait.
Published byΠολύδωρος Κωνσταντίνου Modified over 6 years ago
1
Chapter 4 A Tour of the Cell Lecture by Richard L. Myers
2
Introduction: Cells on the Move
Cells, the simplest collection of matter that can live, were first observed by Robert Hooke in 1665 Antoni van Leeuwenhoek later described cells that could move He viewed bacteria with his own hand-crafted microscopes Leeuwenhoek was a haberdasher who developed the microscope to magnify the cloth he used to make clothing. His greatest contribution to science was his curiosity. As a result, he observed “animalcules” in a variety of liquids and reported his findings to the most prestigious science society of the day, the Royal Society of London. Copyright © 2009 Pearson Education, Inc.
3
Introduction: Cells on the Move
Although cell movement attracted the early scientists, we know today that not all cells move However, the cellular parts are actively moving Cells are dynamic, moving, living systems Copyright © 2009 Pearson Education, Inc.
4
Introduction: Cells on the Move
The early microscopes provided data to establish the cell theory That is, all living things are composed of cells and that all cells come from other cells Life at the cellular level arises from structural order, reflecting emergent properties and the correlation between structure and function. Copyright © 2009 Pearson Education, Inc.
8
INTRODUCTION TO THE CELL
Copyright © 2009 Pearson Education, Inc.
9
4.1 Microscopes reveal the world of the cell
A variety of microscopes have been developed for a clearer view of cells and cellular structure The most frequently used microscope is the light microscope (LM)—like the one used in biology laboratories Light passes through a specimen then through glass lenses into the viewer’s eye Specimens can be magnified up to 1,000 times the actual size of the specimen With today’s modern light microscopes, images can be directed onto photographic film or a digital sensor, or onto a video screen. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of resolution and magnification. However, pixels and resolution of digital images can help clarify the distinction. Consider printing the same image at high and low resolution and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, etc. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes (they need not state their answers publicly, to avoid embarrassment). 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope, and a compound light microscope using microscope slides. The way these scopes function parallels the workings of electron microscopes. Dissection microscopes are like a SEM—both rely upon a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye the same way a compound light microscope or TEM works! Copyright © 2009 Pearson Education, Inc.
10
Eyepiece Enlarges image formed by objective lens Ocular lens
Magnifies specimen, forming primary image Objective lens Specimen Condenser lens Focuses light through specimen Figure 4.1A Light microscope (LM) Light source
11
4.1 Microscopes reveal the world of the cell
Microscopes have limitations Both the human eye and the microscope have limits of resolution—the ability to distinguish between small structures Therefore, the light microscope cannot provide the details of a small cell’s structure The human eye cannot resolve details finer than 0.1 mm. The light microscope can resolve objects as small as 0.2 micrometers. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of resolution and magnification. However, pixels and resolution of digital images can help clarify the distinction. Consider printing the same image at high and low resolution and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, etc. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes (they need not state their answers publicly, to avoid embarrassment). 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope, and a compound light microscope using microscope slides. The way these scopes function parallels the workings of electron microscopes. Dissection microscopes are like a SEM—both rely upon a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye the same way a compound light microscope or TEM works! Copyright © 2009 Pearson Education, Inc.
12
Figure 4.1B Light micrograph of a protist, Paramecium.
13
4.1 Microscopes reveal the world of the cell
Biologists often use a very powerful microscope called the electron microscope (EM) to view the ultrastructure of cells It can resolve biological structures as small as 2 nanometers and can magnify up to 100,000 times Instead of light, the EM uses a beam of electrons Two EM microscopes are routinely used. One is the transmission electron microscope (TEM), which is used to study internal cell structure, and the other is the scanning electron microscope (SEM), which is used to study the architecture of cell surfaces. Student Misconceptions and Concerns 1. Students typically cannot distinguish between the concepts of resolution and magnification. However, pixels and resolution of digital images can help clarify the distinction. Consider printing the same image at high and low resolution and enlarging the same image at two different levels of resolution. Teaching Tip 2 below suggests another related exercise. Teaching Tips 1. Challenge students to identify other examples of technology that have extended our senses. Chemical probes can identify what we cannot taste, listening devices detect what we do not normally hear, night vision and ultraviolet (UV) cameras see or magnify wavelengths beyond our vision, etc. Students can be assigned the task of preparing a short report on one of these technologies. 2. Here is a chance to demonstrate resolving power in the classroom. Use a marker and your classroom marker board to make several pairs of dots separated by shorter and shorter distances. Start out with two dots clearly separated apart—perhaps by 4–5 cm—and end with a pair of dots that touch. Label them a, b, c, etc. Ask your students to indicate the letters of the pairs of points that they can distinguish as separate; this is the definition of resolution for their eyes (they need not state their answers publicly, to avoid embarrassment). 3. Most biology laboratories have two types of microscopes for student use: a dissection (or stereo-) microscope, and a compound light microscope using microscope slides. The way these scopes function parallels the workings of electron microscopes. Dissection microscopes are like a SEM—both rely upon a beam reflected off a surface. As you explain this to your class, hold up an object, identify a light source in the room, and explain that our eyes see most images when our eyes detect light that has reflected off the surface of an object. Compound light microscopes are like TEMs, in which a beam is transmitted through a thin sheet of material. If you have an overhead or other strong light source, hold up a piece of paper between your eye and the light source. You will see the internal detail of the paper as light is transmitted through the paper to your eye the same way a compound light microscope or TEM works! Copyright © 2009 Pearson Education, Inc.
14
Table 4.1 Measurement equivalents
15
Figure 4.1C Scanning electron micrograph of Paramecium.
16
Figure 4.1D Transmission electron micrograph of Paramecium.
17
Figure 4.1E Micrograph produced by differential interference-contrast microscopy of Paramecium.
18
Figure 4.1F Micrograph produced by fluorescence confocal microscopy, showing nerve cells growing in tissue culture.
19
4.2 Most cells are microscopic
Most cells cannot be seen without a microscope Bacteria are the smallest of all cells and require magnifications up to 1,000X Plant and animal cells are 10 times larger than most bacteria Because it is difficult to study the functions of cell components in intact cells, scientists have developed techniques to isolate specific cell components for study of functions. For BLAST Animation Eukaryotic Cell Shape and Surface Area, go to Animation and Video Files. Teaching Tips 1. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter is to a micron: 1,000 to 1. 2. Here is another way to explain surface-to-volume ratios. Have your class consider this situation. You purchase a set of eight coffee mugs, each in its own cubic box, for a wedding present. You can wrap the eight boxes together as one large cube, or wrap each of the eight boxes separately. Either way, you will be wrapping the same volume. However, wrapping the mugs separately requires much more paper. This is because the surface-to-volume ratio is greater for smaller objects. Copyright © 2009 Pearson Education, Inc.
20
10 m 1 m Unaided eye 100 mm (10 cm) 10 mm (1 cm) 1 mm 100 µm
Human height 1 m Length of some nerve and muscle cells 100 mm (10 cm) Unaided eye Chicken egg 10 mm (1 cm) Frog egg 1 mm 100 µm Most plant and animal cells Light microscope 10 µm Nucleus Most bacteria Mitochondrion 1 µm Figure 4.2A The sizes of cells and related objects. Mycoplasmas (smallest bacteria) Electron microscope 100 nm Viruses Ribosome 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms
21
4.2 Most cells are microscopic
The surface area of a cell is important for carrying out the cell’s functions, such as acquiring adequate nutrients and oxygen A small cell has more surface area relative to its cell volume and is more efficient The need to service the cell’s volume explains the importance of the microscopic size of cells. For the BLAST Animation Eukaryotic Cell Shape and Surface Area, go to Animation and Video Files. For the BLAST Animation Surface Area to Volume Calculator, go to Animation and Video Files. Teaching Tips 1. Even in college, students still struggle with the metric system. When discussing the scale of life, consider bringing a meter stick to class. The ratio of a meter to a millimeter is the same as the ratio of a millimeter is to a micron: 1,000 to 1. 2. Here is another way to explain surface-to-volume ratios. Have your class consider this situation. You purchase a set of eight coffee mugs, each in its own cubic box, for a wedding present. You can wrap the eight boxes together as one large cube, or wrap each of the eight boxes separately. Either way, you will be wrapping the same volume. However, wrapping the mugs separately requires much more paper. This is because the surface-to-volume ratio is greater for smaller objects. Copyright © 2009 Pearson Education, Inc.
22
10 µm 30 µm 10 µm 30 µm Surface area Total surface area
Figure 4.2B Effect of cell size on surface area. Surface area of one large cube = 5,400 µm2 Total surface area of 27 small cubes = 16,200 µm2
23
4.3 Prokaryotic cells are structurally simpler than eukaryotic cells
Bacteria and archaea are prokaryotic cells All other forms of life are eukaryotic cells Both prokaryotic and eukaryotic cells have a plasma membrane and one or more chromosomes and ribosomes Eukaryotic cells have a membrane-bound nucleus and a number of other organelles, whereas prokaryotes have a nucleoid and no true organelles Bacteria have a single chromosome that is found within the cell in the form of a circle (no free ends). They have extrachromosomal DNA called plasmids, but they are not necessary for viability of the cell. Students should be reminded that there are possible evolutionary relationships between prokaryotic and eukaryotic cells and questioned about these relationships. Did eukaryotic cells evolve from bacteria-like organisms or perhaps Archaea? For the BLAST Animation Prokaryotic Cell Size, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students often think of the function of cell membranes as mainly containment, like that of a plastic bag. Consider relating the functions of membranes to our human skin. (For example, both membranes and our skin detect stimuli, engage in gas exchange, and serve as sites of excretion and absorption.) Teaching Tips 1. A visual comparison of prokaryotic and eukaryotic cells, such as that found in Figure 1.4, can be very helpful when discussing the key differences between these cell types. These cells are strikingly different in size and composition. Providing students with a visual reference point rather than simply listing these traits will help them better retain this information. 2. Students might wrongly conclude that prokaryotes are typically one-tenth the volume of eukaryotic cells. A difference in diameter of a factor of ten translates into a much greater difference in volume. If students recall enough geometry, you may want to challenge them to calculate the difference in the volume of two cells with diameters that differ by a factor of ten. 3. Germs—here is a term that we learn early in our lives but that is rarely well-defined. Students may appreciate a biological explanation. The general use of germs is a reference to anything that causes disease. This may be a good time to sort the major disease-causing agents into three categories: (1) bacteria (prokaryotes), (2) viruses (not yet addressed), and (3) single-celled and multicellular eukaryotes (athlete’s foot is a fungal infection; malaria is caused by a unicellular eukaryote). 4. Module 4.3 mentions how antibiotics can specifically target prokaryotic but not eukaryotic cells, providing a good segue into discussion of the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at Copyright © 2009 Pearson Education, Inc.
24
A thin section through the bacterium Bacillus coagulans (TEM)
Pili Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule Figure 4.3 A structural diagram (left) and electron micrograph (right) of a typical prokaryotic cell. Module 4.3 mentions how antibiotics can specifically target prokaryotic but not eukaryotic cells. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at A thin section through the bacterium Bacillus coagulans (TEM) A typical rod-shaped bacterium Flagella
25
Pili Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall
Capsule Figure 4.3 A structural diagram of a typical prokaryotic cell. Module 4.3 mentions how antibiotics can specifically target prokaryotic but not eukaryotic cells. This might be a good time to discuss the evolution of antibiotic resistance. Teaching tips and ideas for related lessons can be found at Flagella
26
4.4 Eukaryotic cells are partitioned into functional compartments
There are four life processes in eukaryotic cells that depend upon structures and organelles Manufacturing Breakdown of molecules Energy processing Structural support, movement, and communication Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.
27
4.4 Eukaryotic cells are partitioned into functional compartments
Manufacturing involves the nucleus, ribosomes, endoplasmic reticulum, and Golgi apparatus Manufacture of a protein, perhaps an enzyme, involves all of these The nuclear DNA directs protein synthesis by first transcribing DNA into mRNA. The mRNA reaches the ribosomes, which translate the genetic message into a protein. The entire process of transcription and translation requires enzymes, whose synthesis was also directed by DNA. The endoplasmic reticulum and Golgi apparatus further process the proteins. Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.
28
4.4 Eukaryotic cells are partitioned into functional compartments
Breakdown of molecules involves lysosomes, vacuoles, and peroxisomes Breakdown of an internalized bacterium by a phagocytic cell would involve all of these Lysosomes, vacuoles, and peroxisomes involve digestion by hydrolytic enzymes of unwanted materials within the cell, resulting in products that are used by the cell as food. Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.
29
4.4 Eukaryotic cells are partitioned into functional compartments
Energy processing involves mitochondria in animal cells and chloroplasts in plant cells Generation of energy-containing molecules, such as adenosine triphosphate, occurs in mitochondria and chloroplasts Although mitochondria and chloroplasts are enclosed by membranes, they are not part of the endomembrane system. Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.
30
4.4 Eukaryotic cells are partitioned into functional compartments
Structural support, movement, and communication involve the cytoskeleton, plasma membrane, and cell wall An example of the importance of these is the response and movement of phagocytic cells to an infected area Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.
31
4.4 Eukaryotic cells are partitioned into functional compartments
Membranes within a eukaryotic cell partition the cell into compartments, areas where cellular metabolism occurs Each compartment is fluid-filled and maintains conditions that favor particular metabolic processes and activities Although the cell is compartmentalized, none of the cell’s components works alone. The cell is a living unit greater than the sum of its parts. Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.
32
4.4 Eukaryotic cells are partitioned into functional compartments
Although there are many similarities between animal and plant cells, differences exist Lysosomes and centrioles are not found in plant cells Plant cells have a rigid cell wall, chloroplasts, and a central vacuole not found in animal cells For the BLAST Animation Animal Cell Overview, go to Animation and Video Files. For the BLAST Animation Plant Cell Overview, go to Animation and Video Files. For the BioFlix Animation Tour of an Animal Cell, go to Animation and Video Files. For the BioFlix Animation Tour of a Plant Cell, go to Animation and Video Files. For the Discovery Video Cells, go to Animation and Video Files. Teaching Tips 1. Some instructors have found that challenging students to come up with analogies for the many eukaryotic organelles is a highly effective teaching method. Students may wish to construct one inclusive analogy between a society or factory and a cell or construct separate analogies for each organelle. As with any analogy, it is important to list the similarities and exceptions. Copyright © 2009 Pearson Education, Inc.
33
NUCLEUS: Nuclear envelope Chromosomes Smooth endoplasmic reticulum
Nucleolus Rough endoplasmic reticulum Lysosome Centriole Ribosomes Figure 4.4A An animal cell. Peroxisome Golgi apparatus CYTOSKELETON: Microtubule Plasma membrane Intermediate filament Mitochondrion Microfilament
34
NUCLEUS: Rough endoplasmic reticulum Nuclear envelope Chromosome
Ribosomes Nucleolus Smooth endoplasmic reticulum Golgi apparatus CYTOSKELETON: Central vacuole Microtubule Chloroplast Intermediate filament Cell wall Plasmodesmata Microfilament Figure 4.4B A plant cell. Mitochondrion Peroxisome Plasma membrane Cell wall of adjacent cell
35
4.5 The structure of membranes correlates with their functions
The plasma membrane controls the movement of molecules into and out of the cell, a trait called selective permeability The structure of the membrane with its component molecules is responsible for this characteristic Membranes are made of lipids, proteins, and some carbohydrate, but the most abundant lipids are phospholipids The plasma membrane provides a good example of the link between the structure of an organelle and its function. One of the earliest episodes in the evolution of life may have been the formation of a membrane. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will naturally seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Furthermore, because of these hydrophobic properties, lipid bilayers are also selfhealing. That the properties of phospholipids emerge from their organization is worth emphasizing to students. 2. You might wish to share a very simple analogy that works very well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) Copyright © 2009 Pearson Education, Inc.
36
Hydrophilic head Phosphate group Symbol Hydrophobic tails
Figure 4.5A Phospholipid molecule. Hydrophobic tails
37
4.5 The structure of membranes correlates with their functions
Phospholipids form a two-layer sheet called a phospholipid bilayer Hydrophilic heads face outward, and hydrophobic tails point inward Thus, hydrophilic heads are exposed to water, while hydrophobic tails are shielded from water Proteins are attached to the surface, and some are embedded into the phospholipid bilayer A major function of the phospholipid bilayer is selective permeability. However, because of their composition, some molecules can simply diffuse across, whereas others need help. The hydrophobic and hydrophilic ends of a phospholipid molecule naturally create a lipid bilayer. The hydrophobic edges of the layer will naturally seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Further, because of these hydrophobic properties, lipid bilayers are naturally self-healing. Teaching Tips 1. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will naturally seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water (a simple cell). Furthermore, because of these hydrophobic properties, lipid bilayers are also selfhealing. That the properties of phospholipids emerge from their organization is worth emphasizing to students. 2. You might wish to share a very simple analogy that works very well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) Copyright © 2009 Pearson Education, Inc.
38
Outside cell Hydrophilic heads Hydrophobic region of protein
tails Inside cell Proteins Figure 4.5B Phospholipid bilayer with associated proteins. Hydrophilic region of protein
39
CELL STRUCTURES INVOLVED IN MANUFACTURING AND BREAKDOWN
Copyright © 2009 Pearson Education, Inc.
40
4.6 The nucleus is the cell’s genetic control center
The nucleus controls the cell’s activities and is responsible for inheritance Inside is a complex of proteins and DNA called chromatin, which makes up the cell’s chromosomes DNA is copied within the nucleus prior to cell division The DNA within the nucleus contains genetic information that must be faithfully replicated and partitioned between two daughter cells to maintain the species. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Noting the main flow of genetic information on the board as DNA → RNA → protein will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, rRNA, mRNA, ribosomes, and proteins are produced in a cell. 2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the door to the boss’s office. 3. Some of your more knowledgeable students may like to guess the exceptions to the rule of 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and adult red blood cells in mammals. 4. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary working copy of the genetic material. In some ways, this is like making a working photocopy of an important document, keeping the original copy safely stored away. Copyright © 2009 Pearson Education, Inc.
41
4.6 The nucleus is the cell’s genetic control center
The nuclear envelope is a double membrane with pores that allow material to flow in and out of the nucleus It is attached to a network of cellular membranes called the endoplasmic reticulum Each of the membranes in the nuclear envelope (membrane) is a lipid bilayer separated by a space of 20–40 nm. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Noting the main flow of genetic information on the board as DNA → RNA → protein will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, rRNA, mRNA, ribosomes, and proteins are produced in a cell. 2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the door to the boss’s office. 3. Some of your more knowledgeable students may like to guess the exceptions to the rule of 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and adult red blood cells in mammals. 4. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary working copy of the genetic material. In some ways, this is like making a working photocopy of an important document, keeping the original copy safely stored away. Copyright © 2009 Pearson Education, Inc.
42
Two membranes of nuclear envelope
Nucleus Nucleolus Chromatin Pore Figure 4.6 TEM (left) and diagram (right) of the nucleus. Endoplasmic reticulum Ribosomes
43
4.7 Ribosomes make proteins for use in the cell and export
Ribosomes are involved in the cell’s protein synthesis Ribosomes are synthesized in the nucleolus, which is found in the nucleus Cells that must synthesize large amounts of protein have a large number of ribosomes An example of a cell that at times must make a large amount of protein is a lymphocyte, a white blood cell. Upon stimulation by infectious agents like bacteria, it pumps out a significant amount of antibody, a protein, to fight the infection. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Consider challenging your students to explain how we can have four main types of organic molecules functioning in specific roles in our cells, yet DNA and RNA only specifically dictate the generation of proteins (and more copies of DNA and RNA). How is the production of specific types of carbohydrates and lipids in cells controlled? (Answer: primarily by the specific properties of enzymes.) Copyright © 2009 Pearson Education, Inc.
44
4.7 Ribosomes make proteins for use in the cell and export
Some ribosomes are free ribosomes; others are bound Free ribosomes are suspended in the cytoplasm Bound ribosomes are attached to the endoplasmic reticulum (ER) associated with the nuclear envelope Ribosomes are complexes of ribosomal RNA and protein. Bound and free ribosomes are structurally identical and can alternate between the two roles. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Consider challenging your students to explain how we can have four main types of organic molecules functioning in specific roles in our cells, yet DNA and RNA only specifically dictate the generation of proteins (and more copies of DNA and RNA). How is the production of specific types of carbohydrates and lipids in cells controlled? (Answer: primarily by the specific properties of enzymes.) Copyright © 2009 Pearson Education, Inc.
45
Endoplasmic reticulum (ER)
Ribosomes Cytoplasm ER Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Figure 4.7 Ribosomes. Small subunit TEM showing ER and ribosomes Diagram of a ribosome
46
4.8 Overview: Many cell organelles are connected through the endomembrane system
The membranes within a eukaryotic cell are physically connected and compose the endomembrane system The endomembrane system includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vacuoles, and the plasma membrane In general, the endomembrane system regulates protein traffic and performs metabolic functions in the cell. It accounts for more than half the total membrane in many eukaryotic cells. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Point out to your students that the endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. Copyright © 2009 Pearson Education, Inc.
47
4.8 Overview: Many cell organelles are connected through the endomembrane system
Some components of the endomembrane system are able to communicate with others with formation and transfer of small membrane segments called vesicles One important result of communication is the synthesis, storage, and export of molecules For the BLAST Animation Vesicle Transport, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Point out to your students that the endoplasmic reticulum is continuous with the outer nuclear membrane. This explains why the ER is usually found close to the nucleus. Copyright © 2009 Pearson Education, Inc.
48
4.9 The endoplasmic reticulum is a biosynthetic factory
There are two kinds of endoplasmic reticulum—smooth and rough Smooth ER lacks attached ribosomes Rough ER lines the outer surface of membranes They differ in structure and function However, they are connected Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory. Copyright © 2009 Pearson Education, Inc.
49
Nuclear envelope Ribosomes Smooth ER Rough ER
Figure 4.9A Smooth and rough endoplasmic reticulum.
50
4.9 The endoplasmic reticulum is a biosynthetic factory
Smooth ER is involved in a variety of diverse metabolic processes For example, enzymes produced by the smooth ER are involved in the synthesis of lipids, oils, phospholipids, and steroids Smooth ER processes include synthesis of lipids, metabolism of carbohydrates, and detoxification of drugs and poisons. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory. Copyright © 2009 Pearson Education, Inc.
51
4.9 The endoplasmic reticulum is a biosynthetic factory
Rough ER makes additional membrane for itself and proteins destined for secretion Once proteins are synthesized, they are transported in vesicles to other parts of the endomembrane system Secreted proteins are important to the multicellular individual. For example, hormones, antibodies, and enzymes are glycoproteins that have significant impacts on homeostasis, protection, or metabolism. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory. Copyright © 2009 Pearson Education, Inc.
52
Transport vesicle buds off Ribosome Secretory protein inside trans-
4 Ribosome Secretory protein inside trans- port vesicle 3 Sugar chain 1 Figure 4.9B Synthesis and packaging of a secretory protein by the rough ER. Glycoprotein 2 Polypeptide Rough ER
53
4.10 The Golgi apparatus finishes, sorts, and ships cell products
The Golgi apparatus functions in conjunction with the ER by modifying products of the ER Products travel in transport vesicles from the ER to the Golgi apparatus One side of the Golgi apparatus functions as a receiving dock for the product and the other as a shipping dock Products are modified as they go from one side of the Golgi apparatus to the other and travel in vesicles to other sites The finished product can become part of the plasma membrane or other organelle, or it may move to the plasma membrane for export from the cell. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Some people think the Golgi apparatus looks like a stack of pita bread. 2. If you continue the factory analogy, the addition of a molecular tag by the Golgi apparatus is like adding address labels in the shipping department of a factory. Copyright © 2009 Pearson Education, Inc.
54
Golgi apparatus “Receiving” side of Golgi Golgi apparatus apparatus
Transport vesicle from ER New vesicle forming Figure 4.10 The Golgi apparatus. You might tell your students that the Golgi apparatus looks like a stack of pita bread. Transport vesicle from the Golgi “Shipping” side of Golgi apparatus
55
4.11 Lysosomes are digestive compartments within a cell
A lysosome is a membranous sac containing digestive enzymes The enzymes and membrane are produced by the ER and transferred to the Golgi apparatus for processing The membrane serves to safely isolate these potent enzymes from the rest of the cell Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. As noted in Module 4.11, lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” Copyright © 2009 Pearson Education, Inc.
56
4.11 Lysosomes are digestive compartments within a cell
One of the several functions of lysosomes is to remove or recycle damaged parts of a cell The damaged organelle is first enclosed in a membrane vesicle Then a lysosome fuses with the vesicle, dismantling its contents and breaking down the damaged organelle Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. As noted in Module 4.11, lysosomes help to recycle damaged cell components. Challenge your students to explain why this is adaptive. Recycling, whether in human society or in our cells, can be an efficient way to reuse materials. The recycled components, which enter the lysosomes in a highly organized form, would require a much greater investment to produce from “scratch.” Animation: Lysosome Formation Copyright © 2009 Pearson Education, Inc.
57
Digestive enzymes Lysosome Plasma membrane
Figure 4.11A Lysosome fusing with a food vacuole and digesting food.
58
Digestive enzymes Lysosome Plasma membrane Food vacuole
Figure 4.11A Lysosome fusing with a food vacuole and digesting food.
59
Digestive enzymes Lysosome Plasma membrane Food vacuole
Figure 4.11A Lysosome fusing with a food vacuole and digesting food.
60
Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole
Figure 4.11A Lysosome fusing with a food vacuole and digesting food.
61
damaged mitochondrion
Lysosome Figure 4.11B Lysosome fusing with vesicle containing damaged organelle and digesting and recycling its contents. Vesicle containing damaged mitochondrion
62
damaged mitochondrion
Lysosome Figure 4.11B Lysosome fusing with vesicle containing damaged organelle and digesting and recycling its contents. Vesicle containing damaged mitochondrion
63
damaged mitochondrion
Lysosome Digestion Figure 4.11B Lysosome fusing with vesicle containing damaged organelle and digesting and recycling its contents. Vesicle containing damaged mitochondrion
64
4.12 Vacuoles function in the general maintenance of the cell
Vacuoles are membranous sacs that are found in a variety of cells and possess an assortment of functions Examples are the central vacuole in plants with hydrolytic functions, pigment vacuoles in plants to provide color to flowers, and contractile vacuoles in some protists to expel water from the cell For the BLAST Animation Vacuoles, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Challenge your students to identify animal cell organelles other than mitochondria that are not involved in the synthesis of proteins. (Vacuoles and peroxisomes are not involved in protein synthesis). Video: Paramecium Vacuole Copyright © 2009 Pearson Education, Inc.
65
Chloroplast Nucleus Central vacuole
Figure 4.12A Central vacuole in a plant cell. Ask your students to identify organelles in animal cells that are not involved in the synthesis of proteins (other than mitochondria). (Vacuoles and peroxisomes are not involved in protein synthesis.)
66
Nucleus Contractile vacuoles
Figure 4.12B Contractile vacuoles in Paramecium, a single-celled organism. Contractile vacuoles
67
4.13 A review of the structures involved in manufacturing and breakdown
The following figure summarizes the relationships among the major organelles of the endomembrane system Student Misconceptions and Concerns 1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence. 2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking. Teaching Tips 1. Challenge students to identify two regions in a cell where detoxification occurs. These were discussed in separate modules. (Answer: SER and peroxisomes). Copyright © 2009 Pearson Education, Inc.
68
Nucleus Nuclear membrane Rough ER Smooth ER Transport vesicle
Figure 4.13 Connections among the organelles of the endomembrane system. Golgi apparatus Lysosome Vacuole Plasma membrane
69
ENERGY-CONVERTING ORGANELLES
Copyright © 2009 Pearson Education, Inc.
70
4.14 Mitochondria harvest chemical energy from food
Cellular respiration is accomplished in the mitochondria of eukaryotic cells Cellular respiration involves conversion of chemical energy in foods to chemical energy in ATP (adenosine triphosphate) Mitochondria have two internal compartments The intermembrane space, which encloses the mitochondrial matrix where materials necessary for ATP generation are found A cell may have thousands of mitochondria. For the BLAST Animation Mitochondria, go to Animation and Video Files. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They might think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. Teaching Tips 1. ATP functions in cells much like money functions in modern societies. Each holds value that can be generated in one place and spent in another. This analogy has been very helpful for many students. 2. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. These outer membranes best correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Copyright © 2009 Pearson Education, Inc.
71
Mitochondrion Outer membrane Intermembrane space Inner membrane
Figure 4.14 The mitochondrion. Inner membrane Cristae Matrix
72
4.15 Chloroplasts convert solar energy to chemical energy
Chloroplasts are the photosynthesizing organelles of plants Photosynthesis is the conversion of light energy to chemical energy of sugar molecules Chloroplasts are partitioned into compartments The important parts of chloroplasts are the stroma, thylakoids, and grana Chloroplasts contain the green pigment chlorophyll, along with enzymes and other molecules that function in the photosynthetic production of sugar. Student Misconceptions and Concerns 1. Students often mistakenly think that chloroplasts are a substitute for mitochondria in plant cells. They might think that cells either have mitochondria or they have chloroplasts. You might challenge this thinking by asking how plant cells generate ATP at night. Teaching Tips 1. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. These outer membranes best correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. Copyright © 2009 Pearson Education, Inc.
73
Chloroplast Stroma Inner and outer membranes Granum Intermembrane
Figure 4.15 The chloroplast. Granum Intermembrane space
74
4.16 EVOLUTION CONNECTION: Mitochondria and chloroplasts evolved by endosymbiosis
When compared, you find that mitochondria and chloroplasts have (1) DNA and (2) ribosomes The structure of both DNA and ribosomes is very similar to that found in prokaryotic cells, and mitochondria and chloroplasts replicate much like prokaryotes The hypothesis of endosymbiosis proposes that mitochondria and chloroplasts were formerly small prokaryotes that began living within larger cells Symbiosis benefited both cell types There is evidence to indicate that the prokaryotic ancestors of mitochondria and chloroplasts probably gained entry to the host cell as undigested prey or internal parasites. With time, a mutually beneficial relationship resulted. Student Misconceptions and Concerns 1. The evidence that mitochondria and chloroplasts evolved from free-living prokaryotes is further supported by the small size of these organelles, similar to the size of a prokaryote. Mitochondria and chloroplasts are therefore helpful in comparing the general size of eukaryotic and prokaryotic cells. You might think of these organelles as built-in comparisons. Teaching Tips 1. Mitochondria and chloroplasts are each wrapped by multiple membranes. In both organelles, the innermost membranes are the sites of greatest molecular activity and the outer membranes have fewer significant functions. These outer membranes best correspond to the plasma membrane of the eukaryotic cells that originally wrapped the free-living prokaryotes during endocytosis. 2. Mitochondria and chloroplasts are not cellular structures that are synthesized in a cell like ribosomes and lysosomes. Instead, mitochondria only come from other mitochondria and chloroplasts only come from other chloroplasts. This is further evidence of the independent evolution of these organelles from free-living ancestral forms. Copyright © 2009 Pearson Education, Inc.
75
Mitochondrion Engulfing of photosynthetic prokaryote Some cells
of aerobic prokaryote Chloroplast Host cell Figure 4.16 Endosymbiotic origin of mitochondria and chloroplasts. Mitochondrion Host cell
76
INTERNAL AND EXTERNAL SUPPORT: THE CYTOSKELETON AND CELL SURFACES
Copyright © 2009 Pearson Education, Inc.
77
Video: Cytoplasmic Streaming
4.17 The cell’s internal skeleton helps organize its structure and activities Cells contain a network of protein fibers, called the cytoskeleton, that functions in cell structural support and motility Scientists believe that motility and cellular regulation result when the cytoskeleton interacts with proteins called motor proteins Motor proteins work with cytoskeletal elements and the plasma membrane to help cells move. Also, vesicles and other organelles travel to their destinations along the cytoskeletal “monorail.” Student Misconceptions and Concerns 1. Students often regard the cytosol as little more than a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. Module 4.17 describes the dynamic and diverse functions of the cytoskeleton. Teaching Tips 1. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have a structural framework that is routinely constructed, deconstructed, and then reconstructed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then reconstructed repeatedly, but typically rely upon the same basic design.) Thus, caution is especially warranted when using such analogies. Video: Cytoplasmic Streaming Copyright © 2009 Pearson Education, Inc.
78
Receptor for motor protein
Vesicle ATP Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton (a) Microtubule Vesicles 0.25 µm Campbell, Neil, and Jane Reece, Biology, 8th ed., Figure 6.21 Motor proteins and the cytoskeleton. (a) Motor proteins that attach to receptors on vesicles can “walk” the vesicles along microtubules or, in some cases, microfilaments; Vesicles containing neurotransmitters migrate to the tips of nerve cell axons via the mechanism in (a). (b)
79
4.17 The cell’s internal skeleton helps organize its structure and activities
The cytoskeleton is composed of three kinds of fibers Microfilaments (actin filaments) support the cell’s shape and are involved in motility Intermediate filaments reinforce cell shape and anchor organelles Microtubules (made of tubulin) shape the cell and act as tracks for motor protein A specialized arrangement of microtubules in eukaryotes is responsible for the beating of flagella (human sperm) and cilia (cells of the human respiratory tract). Student Misconceptions and Concerns 1. Students often regard the cytosol as little more than a watery fluid that suspends the organelles. The diverse functions of thin, thick, and intermediate filaments are rarely appreciated before college. Module 4.17 describes the dynamic and diverse functions of the cytoskeleton. Teaching Tips 1. Analogies between the infrastructure of human buildings and the cytoskeleton are limited by the dynamic nature of the cytoskeleton. Few human structures have a structural framework that is routinely constructed, deconstructed, and then reconstructed in a new configuration on a regular basis. (Tents are often constructed, deconstructed, and then reconstructed repeatedly, but typically rely upon the same basic design.) Thus, caution is especially warranted when using such analogies Copyright © 2009 Pearson Education, Inc.
80
Intermediate filament Microtubule
Nucleus Nucleus Actin subunit Fibrous subunits Tubulin subunit Figure 4.17 Fibers of the cytoskeleton: microfilaments are stained red (left), intermediate filaments are stained yellow-green (center), and microtubules are stained green (right). 7 nm 10 nm 25 nm Microfilament Intermediate filament Microtubule
81
Actin subunit Microfilament 7 nm
Figure 4.17 Fibers of the cytoskeleton: microfilaments are stained red. Actin subunit 7 nm Microfilament
82
Intermediate filament
Nucleus Figure 4.17 Fibers of the cytoskeleton: intermediate filaments are stained yellow-green. Fibrous subunits 10 nm Intermediate filament
83
Nucleus Tubulin subunit Microtubule 25 nm
Figure 4.17 Fibers of the cytoskeleton: microtubules are stained green. Tubulin subunit 25 nm Microtubule
84
4.18 Cilia and flagella move when microtubules bend
While some protists have flagella and cilia that are important in locomotion, some cells of multicellular organisms have them for different reasons Cells that sweep mucus out of our lungs have cilia Animal sperm are flagellated Student Misconceptions and Concerns 1. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! Video: Paramecium Cilia Video: Chlamydomonas Copyright © 2009 Pearson Education, Inc.
85
Cilia Figure 4.18A Cilia on cells lining the respiratory tract.
86
Flagellum Figure 4.18B Undulating flagellum on a sperm cell.
87
4.18 Cilia and flagella move when microtubules bend
A flagellum propels a cell by an undulating, whiplike motion Cilia, however, work more like the oars of a crew boat Although differences exist, flagella and cilia have a common structure and mechanism of movement Student Misconceptions and Concerns 1. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! Copyright © 2009 Pearson Education, Inc.
88
4.18 Cilia and flagella move when microtubules bend
Both flagella and cilia are made of microtubules wrapped in an extension of the plasma membrane A ring of nine microtubule doublets surrounds a central pair of microtubules This arrangement is called the pattern and is anchored in a basal body with nine microtubule triplets arranged in a ring Student Misconceptions and Concerns 1. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! Animation: Cilia and Flagella Copyright © 2009 Pearson Education, Inc.
89
Cross sections: Outer microtubule doublet Central microtubules
Radial spoke Dynein arms Flagellum Plasma membrane Figure 4.18C Structure of a eukaryotic flagellum or cilium. Triplet Basal body Basal body
90
4.18 Cilia and flagella move when microtubules bend
Cilia and flagella move by bending motor proteins called dynein arms These attach to and exert a sliding force on an adjacent doublet The arms then release and reattach a little further along and repeat this time after time This “walking” causes the microtubules to bend Student Misconceptions and Concerns 1. Students often think that the cilia on the cells lining our trachea function like a comb, removing debris from the air. Except in cases of disease or damage, these respiratory cilia are covered by mucus. Cilia do not reach the air to comb it free of debris. Instead, these cilia sweep dirty mucus up our respiratory tracts to be expelled or swallowed. Teaching Tips 1. Students might enjoy this brief class activity. Have everyone in the class clear their throats at the same time. Wait a few seconds. Have them notice that after clearing, they swallowed. The mucus that trapped debris is swept up the trachea by cilia. When we clear our throats, this dirty mucus is disposed of down our esophagus and among the strong acids of our stomach! Copyright © 2009 Pearson Education, Inc.
91
4.19 CONNECTION: Problems with sperm motility may be environmental or genetic
There has been a decline in sperm quality A group of chemicals called phthalates used in a variety of things people use every day may be the cause On the other hand, there are genetic reasons that sperm lack motility Primary ciliary dyskinesia (PCD) is an example PCD is a rare disease in which there is an absence of dynein arms, which prevents microtubules from bending. Teaching Tips 1. Primary ciliary dyskinesia results in nonmotile cilia. Module 4.19 describes infertility in males due to immotile sperm. Challenge your students to suggest reasons why this same disease might reduce fertility in an affected woman. (In the oviduct, cilia convey the egg along the oviduct toward the uterus.) Copyright © 2009 Pearson Education, Inc.
92
Figure 4.19 Cross section of immotile sperm flagellum.
93
4.20 The extracellular matrix of animal cells functions in support, movement, and regulation
Cells synthesize and secrete the extracellular matrix (ECM) that is essential to cell function The ECM is composed of strong fibers of collagen, which holds cells together and protects the plasma membrane ECM attaches through connecting proteins that bind to membrane proteins called integrins Integrins span the plasma membrane and connect to microfilaments of the cytoskeleton Integrins have the function of “integrating” information from outside to inside the cell and, thus, essentially regulate a cell’s behavior. Student Misconceptions and Concerns 1. The structure and functions of the extracellular matrix (ECM) are closely associated with the cells that it contacts. Students might suspect that like roots from a tree, cells are anchored to the matrix indefinitely. However, some cells can detach from the ECM and migrate great distances, often following molecular trails (such as fibronectin and laminin) that direct them along the journey. Teaching Tips 1. The extracellular matrix forms a significant structural component of many connective tissues, including cartilage and bone. Many of the properties of cartilage and bone are directly related to the large quantities of material sandwiched between the bone (osteocyte) and cartilage (chondrocyte) cells. Copyright © 2009 Pearson Education, Inc.
94
Glycoprotein complex with long polysaccharide Collagen fiber
EXTRACELLULAR FLUID Collagen fiber Connecting glycoprotein Integrin Plasma membrane Figure 4.20 The extracellular matrix (ECM) of an animal cell. Microfilaments CYTOPLASM
95
4.21 Three types of cell junctions are found in animal tissues
Adjacent cells communicate, interact, and adhere through specialized junctions between them Tight junctions prevent leakage of extracellular fluid across a layer of epithelial cells Anchoring junctions fasten cells together into sheets Gap junctions are channels that allow molecules to flow between cells Teaching Tips 1. Tight junctions form a seal that prevents the movement of fluids past the region of the junction. Functionally, this is similar to the lengthy zipper-like seal at the top of plastic food storage bags. Animation: Desmosomes Animation: Gap Junctions Animation: Tight Junctions Copyright © 2009 Pearson Education, Inc.
96
Tight junctions Anchoring junction Gap junctions Plasma membranes
Figure 4.21 Three types of cell junctions in animal tissues. Plasma membranes of adjacent cells Extracellular matrix
97
4.22 Cell walls enclose and support plant cells
Plant, but not animal cells, have a rigid cell wall It protects and provides skeletal support that helps keep the plant upright against gravity Plant cell walls are composed primarily of cellulose Plant cells have cell junctions called plasmodesmata that serve in communication between cells For the BLAST Animation Signaling: Direct, go to Animation and Video Files. For the BLAST Animation Plant Cell Wall, go to Animation and Video Files. Teaching Tips 1. Consider challenging your students to suggest analogies to the structure and function of plasmodesmata. Critically examining the similarities and differences of their suggestions requires a careful understanding of structure and function. 2. The text in Module 4.22 compares the fibers-in-a-matrix construction of a plant cell wall to fiberglass. Students familiar with highway construction or the pouring of concrete might also be familiar with the frequent use of reinforcing bar (rebar) to similarly reinforce concrete. Copyright © 2009 Pearson Education, Inc.
98
Walls of two adjacent plant cells Vacuole Plasmodesmata
Primary cell wall Figure 4.22 Plant cell walls and cell junction. Secondary cell wall Cytoplasm Plasma membrane
99
FUNCTIONAL CATEGORIES OF CELL STRUCTURES
Copyright © 2009 Pearson Education, Inc.
100
4.23 Review: Eukaryotic cell structures can be grouped on the basis of four basic functions
It is possible to group cell organelles into four categories based on general functions of organelles In each category structure is correlated with function Student Misconceptions and Concerns 1. Students can easily feel overwhelmed by the large numbers of structures and related functions in this chapter. For such students, Module 4.23 might be the best place to start when approaching this chapter. Students might best comprehend the content in Chapter 4 by reviewing the categories of organelles and related functions in Table 4.23 and referring to it regularly as the chapter is studied and/or discussed. Teaching Tips 1. The chapter ends by noting the three fundamental features of all organisms. Challenge students to explain if viruses are organisms according to this definition. 2. Some students might benefit by creating a concept map integrating the information in Table Such a map would note the components of a cell interconnected by lines and relationships between these cellular components. Such techniques may also be beneficial in later chapters, depending upon the learning style of particular students. Copyright © 2009 Pearson Education, Inc.
101
Table 4.23 Eukaryotic Cell Structures and Functions.
104
a. l. b. c. k. j. i. h. d. g. e. f.
105
You should now be able to
Describe microscopes and their importance in viewing cellular structure Distinguish between prokaryotic and eukaryotic cells Describe the structure of cell membranes and how membrane structure relates to function Discuss ways that cellular organelles are involved in the manufacture and breakdown of important cellular molecules Copyright © 2009 Pearson Education, Inc.
106
You should now be able to
List cell structures involved in manufacture and breakdown of important cellular materials Describe the function of each cellular organelle that is involved in manufacture and breakdown of important cellular materials List cell structures involved in energy conversion Describe the function of each cellular organelle that is involved in energy conversion Copyright © 2009 Pearson Education, Inc.
107
You should now be able to
List cell structures involved in internal and external support of cells Describe the function of each cellular organelle that is involved in internal and external support of the cell Copyright © 2009 Pearson Education, Inc.
Similar presentations
© 2025 SlidePlayer.com Inc.
All rights reserved.