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Chapter 6 A Tour of the Cell
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Overview: The Fundamental Units of Life
All organisms are made of cells The cell is the simplest collection of matter that can be alive Cell structure is correlated to cellular function All cells are related by their descent from earlier cells For the Discovery Video Cells, go to Animation and Video Files. © 2011 Pearson Education, Inc.
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Figure 6.1 Figure 6.1 How do your brain cells help you learn about biology?
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Concept 6.1: Biologists use microscopes and the tools of biochemistry to study cells
Though usually too small to be seen by the unaided eye, cells can be complex © 2011 Pearson Education, Inc.
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Microscopy Scientists use microscopes to visualize cells too small to see with the naked eye In a light microscope (LM), visible light is passed through a specimen and then through glass lenses Lenses refract (bend) the light, so that the image is magnified © 2011 Pearson Education, Inc.
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Three important parameters of microscopy
Magnification, the ratio of an object’s image size to its real size Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points Contrast, visible differences in parts of the sample © 2011 Pearson Education, Inc.
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Super- resolution microscopy
Figure 6.2 10 m Human height 1 m Length of some nerve and muscle cells 0.1 m Unaided eye Chicken egg 1 cm Frog egg 1 mm Human egg 100 m Most plant and animal cells Light microscopy 10 m Nucleus Most bacteria Mitochondrion 1 m Figure 6.2 The size range of cells. Smallest bacteria Super- resolution microscopy Electron microscopy 100 nm Viruses Ribosomes 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms
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Length of some nerve and muscle cells
Figure 6.2a 10 m Human height 1 m Length of some nerve and muscle cells Unaided eye 0.1 m Chicken egg 1 cm Figure 6.2 The size range of cells. Frog egg 1 mm Human egg 100 m
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Super- resolution microscopy
Figure 6.2b 1 cm Frog egg 1 mm Human egg 100 m Most plant and animal cells Light microscopy 10 m Nucleus Most bacteria Mitochondrion 1 m Smallest bacteria Super- resolution microscopy 100 nm Viruses Electron microscopy Figure 6.2 The size range of cells. Ribosomes 10 nm Proteins Lipids 1 nm Small molecules Atoms 0.1 nm
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Electron Microscopy (EM)
Figure 6.3 Light Microscopy (LM) Electron Microscopy (EM) Brightfield Confocal Longitudinal section of cilium Cross section of cilium (unstained specimen) Cilia 50 m Brightfield (stained specimen) 50 m 2 m 2 m Transmission electron microscopy (TEM) Scanning electron microscopy (SEM) Deconvolution Phase-contrast 10 m Differential-interference- contrast (Nomarski) Super-resolution Figure 6.3 Exploring: Microscopy Fluorescence 1 m 10 m
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Brightfield (unstained specimen) 50 m Figure 6.3a
Figure 6.3 Exploring: Microscopy
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Brightfield (stained specimen) Figure 6.3b
Figure 6.3 Exploring: Microscopy
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Figure 6.3c Phase-contrast Figure 6.3 Exploring: Microscopy
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Differential-interference- contrast (Nomarski)
Figure 6.3d Differential-interference- contrast (Nomarski) Figure 6.3 Exploring: Microscopy
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Figure 6.3e Fluorescence 10 m Figure 6.3 Exploring: Microscopy
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Figure 6.3f Confocal Figure 6.3 Exploring: Microscopy 50 m
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Figure 6.3g Deconvolution 10 m Figure 6.3 Exploring: Microscopy
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Figure 6.3h Super-resolution Figure 6.3 Exploring: Microscopy 1 m
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2 m Cilia Scanning electron microscopy (SEM) Figure 6.3i
Figure 6.3 Exploring: Microscopy 2 m Scanning electron microscopy (SEM)
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2 m Longitudinal section of cilium Cross section of cilium
Figure 6.3j Longitudinal section of cilium Cross section of cilium Figure 6.3 Exploring: Microscopy 2 m Transmission electron microscopy (TEM)
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LMs can magnify effectively to about 1,000 times the size of the actual specimen
Various techniques enhance contrast and enable cell components to be stained or labeled Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by an LM © 2011 Pearson Education, Inc.
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TEMs are used mainly to study the internal structure of cells
Two basic types of electron microscopes (EMs) are used to study subcellular structures Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen TEMs are used mainly to study the internal structure of cells © 2011 Pearson Education, Inc.
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Recent advances in light microscopy
Confocal microscopy and deconvolution microscopy provide sharper images of three-dimensional tissues and cells New techniques for labeling cells improve resolution © 2011 Pearson Education, Inc.
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Cell Fractionation Cell fractionation takes cells apart and separates the major organelles from one another Centrifuges fractionate cells into their component parts Cell fractionation enables scientists to determine the functions of organelles Biochemistry and cytology help correlate cell function with structure © 2011 Pearson Education, Inc.
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Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min
Figure 6.4 TECHNIQUE Homogenization Tissue cells Homogenate Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min Centrifugation Supernatant poured into next tube Differential centrifugation 20,000 g 20 min 80,000 g 60 min Pellet rich in nuclei and cellular debris Figure 6.4 Research Method: Cell Fractionation 150,000 g 3 hr Pellet rich in mitochondria (and chloro- plasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal membranes) Pellet rich in ribosomes
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TECHNIQUE Homogenization Tissue cells Homogenate Centrifugation
Figure 6.4a TECHNIQUE Homogenization Tissue cells Figure 6.4 Research Method: Cell Fractionation Homogenate Centrifugation
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Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min
Figure 6.4b TECHNIQUE (cont.) Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min Supernatant poured into next tube Differential centrifugation 20,000 g 20 min 80,000 g 60 min Pellet rich in nuclei and cellular debris 150,000 g 3 hr Figure 6.4 Research Method: Cell Fractionation Pellet rich in mitochondria (and chloro- plasts if cells are from a plant) Pellet rich in “microsomes” Pellet rich in ribosomes
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Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions
The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells Protists, fungi, animals, and plants all consist of eukaryotic cells © 2011 Pearson Education, Inc.
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Comparing Prokaryotic and Eukaryotic Cells
Basic features of all cells Plasma membrane Semifluid substance called cytosol Chromosomes (carry genes) Ribosomes (make proteins) © 2011 Pearson Education, Inc.
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Prokaryotic cells are characterized by having
No nucleus DNA in an unbound region called the nucleoid No membrane-bound organelles Cytoplasm bound by the plasma membrane © 2011 Pearson Education, Inc.
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Plasma membrane Cell wall Capsule Flagella
Figure 6.5 Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 m Flagella (a) A typical rod-shaped bacterium (b) A thin section through the bacterium Bacillus coagulans (TEM) Figure 6.5 A prokaryotic cell.
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A thin section through the bacterium Bacillus coagulans (TEM)
Figure 6.5a Figure 6.5 A prokaryotic cell. 0.5 m (b) A thin section through the bacterium Bacillus coagulans (TEM)
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Eukaryotic cells are characterized by having
DNA in a nucleus that is bounded by a membranous nuclear envelope Membrane-bound organelles Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally much larger than prokaryotic cells © 2011 Pearson Education, Inc.
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The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell The general structure of a biological membrane is a double layer of phospholipids © 2011 Pearson Education, Inc.
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TEM of a plasma membrane Outside of cell
Figure 6.6 (a) TEM of a plasma membrane Outside of cell Inside of cell 0.1 m Carbohydrate side chains Hydrophilic region Figure 6.6 The plasma membrane. Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane
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(a) TEM of a plasma membrane
Figure 6.6a Outside of cell Inside of cell 0.1 m Figure 6.6 The plasma membrane. (a) TEM of a plasma membrane
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Metabolic requirements set upper limits on the size of cells
The surface area to volume ratio of a cell is critical As the surface area increases by a factor of n2, the volume increases by a factor of n3 Small cells have a greater surface area relative to volume © 2011 Pearson Education, Inc.
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Surface area increases while total volume remains constant
Figure 6.7 Surface area increases while total volume remains constant 5 1 1 Total surface area [sum of the surface areas (height width) of all box sides number of boxes] 6 150 750 Figure 6.7 Geometric relationships between surface area and volume. Total volume [height width length number of boxes] 1 125 125 Surface-to-volume (S-to-V) ratio [surface area volume] 6 1.2 6
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A Panoramic View of the Eukaryotic Cell
A eukaryotic cell has internal membranes that partition the cell into organelles Plant and animal cells have most of the same organelles BioFlix: Tour of an Animal Cell BioFlix: Tour of a Plant Cell © 2011 Pearson Education, Inc.
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ENDOPLASMIC RETICULUM (ER) Nuclear envelope Rough ER Smooth ER
Figure 6.8a ENDOPLASMIC RETICULUM (ER) Nuclear envelope Rough ER Smooth ER Flagellum NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Figure 6.8 Exploring: Eukaryotic Cells Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome
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Animal Cells Fungal Cells 1 m Parent cell 10 m Cell wall Buds
Figure 6.8b Animal Cells Fungal Cells 1 m Parent cell 10 m Cell wall Buds Vacuole Cell 5 m Nucleus Nucleus Nucleolus Mitochondrion Human cells from lining of uterus (colorized TEM) Yeast cells budding (colorized SEM) A single yeast cell (colorized TEM) Figure 6.8 Exploring: Eukaryotic Cells
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Animal Cells Human cells from lining of uterus (colorized TEM) 10 m
Figure 6.8ba Animal Cells 10 m Cell Nucleus Nucleolus Figure 6.8 Exploring: Eukaryotic Cells Human cells from lining of uterus (colorized TEM)
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Fungal Cells Parent cell Buds 5 m Yeast cells budding (colorized SEM)
Figure 6.8bb Fungal Cells Parent cell Buds 5 m Figure 6.8 Exploring: Eukaryotic Cells Yeast cells budding (colorized SEM)
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A single yeast cell (colorized TEM)
Figure 6.8bc 1 m Cell wall Vacuole Nucleus Mitochondrion Figure 6.8 Exploring: Eukaryotic Cells A single yeast cell (colorized TEM)
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Rough endoplasmic reticulum
Figure 6.8c Nuclear envelope Rough endoplasmic reticulum NUCLEUS Smooth endoplasmic reticulum Nucleolus Chromatin Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments CYTOSKELETON Microtubules Figure 6.8 Exploring: Eukaryotic Cells Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell
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Plant Cells Protistan Cells Figure 6.8d Chlamydomonas (colorized SEM)
Flagella Cell 1 m 5 m 8 m Cell wall Nucleus Chloroplast Nucleolus Mitochondrion Vacuole Nucleus Nucleolus Chloroplast Chlamydomonas (colorized SEM) Cells from duckweed (colorized TEM) Cell wall Chlamydomonas (colorized TEM) Figure 6.8 Exploring: Eukaryotic Cells
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Plant Cells Cell 5 m Cell wall Chloroplast Mitochondrion Nucleus
Figure 6.8da Plant Cells Cell 5 m Cell wall Chloroplast Mitochondrion Nucleus Nucleolus Figure 6.8 Exploring: Eukaryotic Cells Cells from duckweed (colorized TEM)
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Protistan Cells 8 m Chlamydomonas (colorized SEM) Figure 6.8db
Figure 6.8 Exploring: Eukaryotic Cells Chlamydomonas (colorized SEM)
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Chlamydomonas (colorized TEM)
Figure 6.8dc Protistan Cells Flagella 1 m Nucleus Nucleolus Vacuole Chloroplast Figure 6.8 Exploring: Eukaryotic Cells Cell wall Chlamydomonas (colorized TEM)
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Concept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes The nucleus contains most of the DNA in a eukaryotic cell Ribosomes use the information from the DNA to make proteins © 2011 Pearson Education, Inc.
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The Nucleus: Information Central
The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle The nuclear envelope encloses the nucleus, separating it from the cytoplasm The nuclear membrane is a double membrane; each membrane consists of a lipid bilayer © 2011 Pearson Education, Inc.
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Figure 6.9 1 m Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Pore complex Surface of nuclear envelope Ribosome Figure 6.9 The nucleus and its envelope. Close-up of nuclear envelope Chromatin 0.25 m 1 m Pore complexes (TEM) Nuclear lamina (TEM)
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Close-up of nuclear envelope Chromatin
Figure 6.9a Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Pore complex Ribosome Figure 6.9 The nucleus and its envelope. Close-up of nuclear envelope Chromatin
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Surface of nuclear envelope
Figure 6.9b 1 m Nuclear envelope: Inner membrane Outer membrane Nuclear pore Figure 6.9 The nucleus and its envelope. Surface of nuclear envelope
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0.25 m Pore complexes (TEM) Figure 6.9c
Figure 6.9 The nucleus and its envelope.
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1 m Nuclear lamina (TEM) Figure 6.9d
Figure 6.9 The nucleus and its envelope. Nuclear lamina (TEM)
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Pores regulate the entry and exit of molecules from the nucleus
The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein © 2011 Pearson Education, Inc.
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The DNA and proteins of chromosomes are together called chromatin
In the nucleus, DNA is organized into discrete units called chromosomes Each chromosome is composed of a single DNA molecule associated with proteins The DNA and proteins of chromosomes are together called chromatin Chromatin condenses to form discrete chromosomes as a cell prepares to divide The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis © 2011 Pearson Education, Inc.
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Ribosomes: Protein Factories
Ribosomes are particles made of ribosomal RNA and protein Ribosomes carry out protein synthesis in two locations In the cytosol (free ribosomes) On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes) For the Cell Biology Video Staining of Endoplasmic Reticulum, go to Animation and Video Files. © 2011 Pearson Education, Inc.
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Free ribosomes in cytosol
Figure 6.10 0.25 m Free ribosomes in cytosol Endoplasmic reticulum (ER) Ribosomes bound to ER Large subunit Small subunit Figure 6.10 Ribosomes. TEM showing ER and ribosomes Diagram of a ribosome
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Free ribosomes in cytosol
Figure 6.10a 0.25 m Free ribosomes in cytosol Endoplasmic reticulum (ER) Ribosomes bound to ER Figure 6.10 Ribosomes. TEM showing ER and ribosomes
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Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell Components of the endomembrane system Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane These components are either continuous or connected via transfer by vesicles © 2011 Pearson Education, Inc.
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The Endoplasmic Reticulum: Biosynthetic Factory
The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells The ER membrane is continuous with the nuclear envelope There are two distinct regions of ER Smooth ER, which lacks ribosomes Rough ER, surface is studded with ribosomes For the Cell Biology Video ER and Mitochondria in Leaf Cells, go to Animation and Video Files. © 2011 Pearson Education, Inc.
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Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Transitional ER
Figure 6.11 Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Transitional ER Ribosomes Transport vesicle 200 nm Smooth ER Rough ER Figure 6.11 Endoplasmic reticulum (ER).
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Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Transitional ER
Figure 6.11a Smooth ER Rough ER Nuclear envelope Figure 6.11 Endoplasmic reticulum (ER). ER lumen Cisternae Transitional ER Ribosomes Transport vesicle
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200 nm Smooth ER Rough ER Figure 6.11b
Figure 6.11 Endoplasmic reticulum (ER).
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Functions of Smooth ER The smooth ER Synthesizes lipids
Metabolizes carbohydrates Detoxifies drugs and poisons Stores calcium ions © 2011 Pearson Education, Inc.
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Functions of Rough ER The rough ER
Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates) Distributes transport vesicles, proteins surrounded by membranes Is a membrane factory for the cell © 2011 Pearson Education, Inc.
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The Golgi Apparatus: Shipping and Receiving Center
The Golgi apparatus consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles For the Cell Biology Video ER to Golgi Traffic, go to Animation and Video Files. For the Cell Biology Video Golgi Complex in 3D, go to Animation and Video Files. For the Cell Biology Video Secretion From the Golgi, go to Animation and Video Files. © 2011 Pearson Education, Inc.
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cis face (“receiving” side of Golgi apparatus)
Figure 6.12 cis face (“receiving” side of Golgi apparatus) 0.1 m Cisternae Figure 6.12 The Golgi apparatus. trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus
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0.1 m TEM of Golgi apparatus Figure 6.12a
Figure 6.12 The Golgi apparatus. TEM of Golgi apparatus
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Lysosomes: Digestive Compartments
A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids Lysosomal enzymes work best in the acidic environment inside the lysosome Animation: Lysosome Formation © 2011 Pearson Education, Inc.
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A lysosome fuses with the food vacuole and digests the molecules
Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole A lysosome fuses with the food vacuole and digests the molecules Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy For the Cell Biology Video Phagocytosis in Action, go to Animation and Video Files. © 2011 Pearson Education, Inc.
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Figure 6.13 Figure 6.13 Lysosomes.
Vesicle containing two damaged organelles 1 m Nucleus 1 m Mitochondrion fragment Lysosome Peroxisome fragment Digestive enzymes Lysosome Lysosome Peroxisome Plasma membrane Figure 6.13 Lysosomes. Digestion Food vacuole Mitochondrion Digestion Vesicle (a) Phagocytosis (b) Autophagy
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1 m Nucleus Lysosome Digestive enzymes Lysosome Plasma membrane
Figure 6.13a 1 m Nucleus Lysosome Digestive enzymes Figure 6.13 Lysosomes. Lysosome Plasma membrane Digestion Food vacuole (a) Phagocytosis
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Figure 6.13aa 1 m Nucleus Figure 6.13 Lysosomes. Lysosome
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Vesicle containing two damaged organelles
Figure 6.13b Vesicle containing two damaged organelles 1 m Mitochondrion fragment Peroxisome fragment Lysosome Figure 6.13 Lysosomes. Peroxisome Digestion Mitochondrion Vesicle (b) Autophagy
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Vesicle containing two damaged organelles
Figure 6.13bb Vesicle containing two damaged organelles 1 m Mitochondrion fragment Figure 6.13 Lysosomes. Peroxisome fragment
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Vacuoles: Diverse Maintenance Compartments
A plant cell or fungal cell may have one or several vacuoles, derived from endoplasmic reticulum and Golgi apparatus © 2011 Pearson Education, Inc.
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Food vacuoles are formed by phagocytosis
Contractile vacuoles, found in many freshwater protists, pump excess water out of cells Central vacuoles, found in many mature plant cells, hold organic compounds and water Video: Paramecium Vacuole © 2011 Pearson Education, Inc.
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Central vacuole Cytosol Central vacuole Nucleus Cell wall Chloroplast
Figure 6.14 Central vacuole Cytosol Central vacuole Nucleus Figure 6.14 The plant cell vacuole. Cell wall Chloroplast 5 m
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Cytosol Central vacuole Nucleus Cell wall Chloroplast 5 m
Figure 6.14a Cytosol Central vacuole Nucleus Cell wall Figure 6.14 The plant cell vacuole. Chloroplast 5 m
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The Endomembrane System: A Review
The endomembrane system is a complex and dynamic player in the cell’s compartmental organization © 2011 Pearson Education, Inc.
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Nucleus Rough ER Smooth ER Plasma membrane Figure 6.15-1
Figure 6.15 Review: relationships among organelles of the endomembrane system. Plasma membrane
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Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi
Figure Nucleus Rough ER Smooth ER cis Golgi Figure 6.15 Review: relationships among organelles of the endomembrane system. Plasma membrane trans Golgi
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Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi
Figure Nucleus Rough ER Smooth ER cis Golgi Figure 6.15 Review: relationships among organelles of the endomembrane system. Plasma membrane trans Golgi
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