Cell Structure and Function

Cell Structure and Function
4 Cell Structure and Function

Chapter 4 At a Glance 4.1 What Is the Cell Theory?
4.2 What Are the Basic Attributes of Cells? 4.3 What Are the Major Features of Eukaryotic Cells? 4.4 What Are the Major Features of Prokaryotic Cells?

4.1 What Is the Cell Theory? The cell theory states that cells are the basic units of life Three principles comprise the cell theory Every living organism is made of one or more cells The smallest organisms are single cells, and cells are the functional units of multicellular organisms All cells arise from preexisting cells

4.2 What Are the Basic Attributes of Cells?
Most cells range in size from about 1 to 100 micrometers in diameter Diffusion is the process whereby molecules dissolved in liquids move from a highly concentrated region to a lesser concentrated region Cells need to exchange nutrients and wastes with the environment No part of the cell can be too far away from the external environment

Figure 4-1 Relative sizes
tallest trees 100 m 10 m 1 m visible with unaided human eye adult human 10 cm 1 cm chicken egg 1 mm frog embryo 100 m light microscope visible with 10 m most eukaryotic cells mitochondrion 1 m visible with conventional electron microscope most prokaryotic cells 100 nm virus 10 nm visible with special electron microscope proteins 1 nm diameter of DNA double helix Units of measurement: 1 meter (m)  inches 1 centimeter (cm)  1/100 m 1 millimeter (mm)  1/1,000 m 1 micrometer (m)  1/1,000,000 m 1 nanometer (nm)  1/1,000,000,000 m 0.1 nm atoms 5

All cells share common features Include plasma membrane Include cytoplasm Use DNA as hereditary blueprint Use RNA to copy the blueprint and guide construction of cell parts

All cells share common features (continued) The plasma membrane encloses the cell and allows interactions between the cell and its environment This structure is composed of lipid, protein, and carbohydrate molecules, and regulates the passage of ions and molecules in and out of cells

Figure 4-2 The plasma membrane
interstitial fluid (outside) carbohydrate glycoprotein A phospholipid bilayer helps to isolate the cell’s contents Proteins help the cell communicate with its environment channel protein membrane protein cytoskeleton cytosol 8

All cells share common features (continued) All cells contain cytoplasm The cytoplasm consists of all the fluid and structures that lie inside the plasma membrane but outside of the nucleus The fluid portion of the cytoplasm (cytosol) contains water, salts, and organic molecules Most of the cell’s metabolic activities occur in the cell cytoplasm

Figure 4-3 A generalized animal cell
nuclear envelope microfilaments nuclear pore nucleus chromatin (DNA) cytosol nucleolus microtubules (cytoskeleton) flagellum (propels sperm cell) basal body rough endoplasmic reticulum vesicle intermediate filaments (cytoskeleton) cytoplasm centriole Golgi apparatus ribosomes on rough ER polyribosome lysosome smooth endoplasmic reticulum vesicles releasing substances from the cell mitochondrion plasma membrane free ribosome 10

Figure 4-4 A generalized plant cell
nuclear envelope ribosomes nuclear pore nucleus intermediate filaments (cytoskeleton) chromatin nucleolus microtubules (cytoskeleton) cell walls of adjoining plant cells chloroplast cytoplasm rough endoplasmic reticulum smooth endoplasmic reticulum Golgi apparatus central vacuole vesicle mitochondrion plasma membrane plasmodesmata cell wall plastid free ribosome cytosol 11

BioFlix Animation: Tour of a Plant Cell

BioFlix Animation: Tour of a Animal Cell

All cells share common features (continued) All cells use DNA as a hereditary blueprint and RNA to copy the blueprint and guide construction of cell parts All cells use DNA (deoxyribonucleic acid) as a hereditary blueprint All cells use RNA (ribonucleic acid) to copy the blueprint and to guide construction of proteins

There are two basic types of cells: prokaryotic and eukaryotic Prokaryotic (“before the nucleus”) cells form the bodies of bacteria and archaea, the simplest forms of life Eukaryotic (“true nucleus”) cells form the bodies of animals, plants, fungi, and protists

There are two basic types of cells: prokaryotic and eukaryotic (continued) The cytoplasm of eukaryotic cells includes a variety of organelles, such as the nucleus and mitochondria The cytoskeleton gives shape and organization to the cytoplasm of eukaryotic cells

Table 4-1 17

4.3 What Are the Major Features of Eukaryotic Cells?
Eukaryotic cells make up the bodies of animals, plants, protists, and fungi Eukaryotic cells are very diverse The cytoplasm of eukaryotic cells houses the nucleus and mitochondria that perform specific functions within the cell Plant and animal cells have structures that are unique to each type of cell

Some eukaryotic cells are supported by cell walls The outer surfaces of plants, fungi, and some protists are covered with nonliving, relatively stiff coatings called cell walls Plant cell walls are composed of cellulose and other polysaccharides Fungal cell walls are made of polysaccharides and chitin

Some eukaryotic cells are supported by cell walls (continued) Plant cells are surrounded by a cell wall Plant cells also have plastids and a central vacuole, not found in animal cells Some animal cells possess vesicles, vacuoles, and cilia, not found in plant cells

Some eukaryotic cells are supported by cell walls (continued) Cell walls are porous, allowing oxygen, carbon dioxide, and water carrying dissolved molecules to flow easily through them The plasma membrane is located just beneath the cell wall

The cytoskeleton provides shape, support, and movement Organelles are attached to a network of protein fibers that make up the cytoskeleton The cytoskeleton is composed of three types of protein fibers Thin microfilaments Medium-sized intermediate filaments Thick microtubules

Figure 4-5 The cytoskeleton
microtubules (red) intermediate filaments microtubules nucleus microfilaments microfilaments (blue) Cytoskeleton Light micrograph showing the cytoskeleton 23

Table 4-2 24

The cytoskeleton provides shape, support, and movement (continued) The cytoskeleton regulates the following cell properties: Cell shape Cell movement Organelle movement Cell division

Cilia and flagella move the cell through fluid or move fluid past the cell Both cilia and flagella are hair-like structures that propel cells through fluids or move fluids past cells They arise from a basal body, which anchors them to the plasma membrane Basal bodies are derived from centrioles, which are identical in structure to basal bodies

Figure 4-6 Cilia and flagella
protein sidearms central pair of microtubules fused microtubule pair section of cilium 0.1 micrometer Paramecium cilium plasma membrane basal body (extends into cytoplasm) 27

Cilia and flagella move the cell through fluid or move fluid past the cell (continued) The force generated by cilia can be compared to that created by oars on the sides of a rowboat The force generated by a flagellum can be compared to that created by the engine on a motorboat Flagella are longer than cilia, and cells with flagella usually have only one or two

Cilia and flagella move the cell through fluid or move fluid past the cell (continued) Some unicellular organisms, such as Paramecium, use cilia to swim through water; others use flagella Ciliated cells line such diverse structures as the gills of oysters, the oviducts of female mammals, and the respiratory tracts of land vertebrates Most animal sperm rely on flagella for movement

Figure 4-7 How cilia and flagella move
cilia lining trachea propulsion of fluid mucus-secreting cells power stroke return stroke Cilium plasma membrane direction of locomotion propulsion of fluid flagellum of human sperm Flagellum continuous propulsion 30

The nucleus, containing DNA, is the control center of the eukaryotic cell The nucleus is the control center of the eukaryotic cell and has three major parts Nuclear envelope Chromatin Nucleolus

The nucleus, containing DNA, is the control center of the eukaryotic cell (continued) The nuclear envelope allows selective exchange of materials The nucleus is isolated from the rest of the cell by a nuclear envelope that consists of a double membrane perforated by nuclear pores The membrane is perforated with tiny protein-lined nuclear pores that allow water, ions, and small molecules to pass freely Passage of proteins, pieces of ribosomes, and RNA are regulated by gatekeeper proteins called the nuclear pore complex that line each nuclear pore

The nucleus Nucleus of a yeast cell Figure 4-8 The nucleus 33 nuclear
envelope nuclear pores nucleolus ribosomes nucleus chromatin nuclear pores with nuclear pore complex The nucleus Nucleus of a yeast cell 33

The nucleus, containing DNA, is the control center of the eukaryotic cell (continued) Chromatin consists of strands of DNA associated with proteins Chromatin is a colored substance contained in the nucleus During cell division, chromatin becomes compacted into long strands called chromosomes The chromosomes contain genes that provide a blueprint for a huge variety of proteins

The nucleus, containing DNA, is the control center of the eukaryotic cell (continued) Because proteins are synthesized in the cytoplasm, copies of the protein blueprints on DNA must leave the nucleus through the nuclear membrane To do this, genetic information in DNA is copied into messenger RNA (mRNA), which travels through the nuclear pores to the cytoplasm, where it directs protein synthesis

Figure 4-9 Chromosomes chromatin chromosome 36

The nucleus, containing DNA, is the control center of the eukaryotic cell (continued) The nucleolus is the site of ribosome assembly Eukaryotic nuclei contain at least one nucleolus, the site of protein synthesis A ribosome is a small particle composed of ribosomal RNA and proteins The nucleolus consists of ribosomal RNA, proteins, ribosomes in various stages of synthesis, and DNA

ribosome mRNA polyribosome growing protein amino acid
Figure 4-10 Ribosomes ribosome mRNA polyribosome growing protein amino acid 38

The eukaryotic cytoplasm contains membranes that form the endomembrane system The endomembrane system segregates molecules from the surrounding cytosol to ensure the orderly occurrences of biochemical processes The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and vacuoles

The eukaryotic cytoplasm contains membranes that form the endomembrane system (continued) Vesicles are membranous sacs transporting molecules to the various regions of the membrane system Exocytosis is the process whereby vesicles fuse with the plasma membrane as they export their contents outside the cell Endocytosis is the process whereby the plasma membrane extends and surrounds material just outside the cell, fuses, and then pinches off to form a vesicle inside the cell

The eukaryotic cytoplasm contains membranes that form the endomembrane system (continued) The endoplasmic reticulum forms membrane-enclosed channels within the cytoplasm The endoplasmic reticulum (ER) is a series of interconnected membranes that form a labyrinth of flattened sacs and channels within the cytoplasm The rough endoplasmic reticulum and smooth endoplasmic reticulum are the two types of ER All the proteins and phospholipids of cell membranes are synthesized in the ER

Figure 4-11 Endoplasmic reticulum
ribosomes smooth ER rough ER rough ER smooth ER vesicles Endoplasmic reticulum may be rough or smooth Smooth and rough ER 42

The eukaryotic cytoplasm contains membranes that form the endomembrane system (continued) Rough endoplasmic reticulum is studded with ribosomes and produces proteins destined for other membranes or for secretion Smooth endoplasmic reticulum has no ribosomes, detoxifies drugs, and synthesizes lipids such as steroid hormones made from cholesterol

The eukaryotic cytoplasm contains membranes that form the endomembrane system (continued) The Golgi apparatus modifies, sorts, and packages important molecules The Golgi apparatus modifies some molecules, such as adding a carbohydrate group to proteins, and making glycoproteins; it breaks some proteins into smaller peptides

The eukaryotic cytoplasm contains membranes that form the endomembrane system (continued) The Golgi apparatus modifies, sorts, and packages important molecules (continued) It separates various proteins and lipids received from the ER according to their destinations It packages the finished molecules into vesicles that are then transported to other parts of the cell or to the plasma membrane for export

Figure 4-12 The Golgi apparatus
Protein-carrying vesicles from the ER merge with the Golgi apparatus Golgi apparatus Vesicles carrying modified protein leave the Golgi apparatus 46

The eukaryotic cytoplasm contains membranes that form the endomembrane system (continued) Secreted proteins are modified as they move through the cell Secreted proteins, like antibodies, are made in the rough ER, travel through Golgi, and then are exported through the plasma membrane Antibodies are glycoproteins produced by white blood cells that attach to foreign invaders to destroy them

Figure 4-13 A protein is manufactured and exported
(interstitial fluid) Vesicles merge with the plasma membrane and release antibodies into the interstitial fluid (cytosol) Completed glycoprotein antibodies are packaged into vesicles on the opposite side of the Golgi apparatus vesicles Golgi apparatus Vesicles fuse with the Golgi apparatus, and carbohydrates are added as the protein passes through the compartments The protein is packaged into vesicles and travels to the Golgi apparatus forming vesicle Antibody protein is synthesized on ribosomes and is transported into channels of the rough ER 48

The eukaryotic cytoplasm contains membranes that form the endomembrane system (continued) Lysosomes serve as the cell’s digestive system Digestive proteins are made in the rough ER, travel through the Golgi, and are packaged in membrane-enclosed vesicles as lysosomes A lysosome fuses with a food vacuole and digests food into basic nutrients

Figure 4-14 Formation and function of lysosomes and food vacuoles via the endomembrane system
(interstitial fluid) food A lysosome fuses with a food vacuole, and the enzymes digest the food (cytosol) food vacuoles The enzymes are delivered to the lysosome in vesicles lysosome The Golgi apparatus modifies the enzymes for export to the lysosomes Golgi apparatus The enzymes are packaged into vesicles and travel to the Golgi apparatus digestive enzymes Digestive enzymes are synthesized on ribosomes and travel through the rough ER 50

Vacuoles serve many functions, including water regulation, storage, and support Many freshwater organisms possess contractile vacuoles composed of collecting ducts, a central reservoir, and a tube leading to a pore in the plasma membrane that carries excess water out of the organism Cellular energy is used to pump salts from the cytoplasm of the protist into collecting ducts A full contractile vacuole contracts, squirting water out through a pore in the plasma membrane 51

Figure 4-15 A contractile vacuole
Water enters the collecting ducts and fills the central reservoir Paramecium collecting ducts central reservoir pore The reservoir contracts, expelling water through the pore Contractile vacuole 52

Vacuoles serve many functions, including water regulation, storage, and support (continued) Plant cells have central vacuoles A large central vacuole occupies three-quarters or more of the volume of most mature plant cells and has several functions Central vacuoles provide support for plant cells Turgor pressure (water pressure), within the vacuole, pushes the fluid portion of the cytoplasm up against the cell wall 53

Vacuoles serve many functions, including water regulation, storage, and support (continued) Plant cells have central vacuoles (continued) The functions of the central vacuole include To maintain water balance To store hazardous wastes, nutrients, or pigments To provide turgor pressure on the cytoplasm to keep cells rigid 54

Mitochondria extract energy from food molecules, and chloroplasts capture solar energy All eukaryotic cells have mitochondria that capture energy stored in sugar by producing high-energy ATP molecules The cells of plants also have chloroplasts, which can capture energy directly from sunlight and store it in sugar molecules Biologists believe that both mitochondria and chloroplasts evolved from prokaryotic bacteria that became incorporated into the cytoplasm of other prokaryotic cells (endosymbiont hypothesis)

Mitochondria extract energy from food molecules, and chloroplasts capture solar energy (continued) The endosymbiont hypothesis Both mitochondria and chloroplasts are about the size of prokaryotic cells (1–5 micrometers in diameter) Both have a double membrane, the outer possibly coming from the host cell and the inner from the guest cell Both have enzymes to synthesize ATP Both possess DNA and ribosomes

Mitochondria extract energy from food molecules, and chloroplasts capture solar energy (continued) Mitochondria are organelles that function as “powerhouses of the cell” Mitochondria extract energy from food molecules The extracted energy is stored in high-energy bonds of ATP The energy extraction process involves anaerobic (“without oxygen”) and aerobic (“with oxygen”) reactions

Mitochondria extract energy from food molecules, and chloroplasts capture solar energy (continued) The inner membrane is folded into cristae The intermembrane compartment lies between inner and outer membranes The matrix space is within the inner membrane

Figure 4-16 A mitochondrion
outer membrane inner membrane intermembrane space matrix cristae 0.1 micrometer 59

Mitochondria extract energy from food molecules, and chloroplasts capture solar energy (continued) Chloroplasts are the sites of photosynthesis Chloroplasts are specialized organelles surrounded by a double membrane The outer membrane separates the organelle from the cytoplasm The inner membrane encloses the fluid stroma and contains stacked, hollow, membranous sacs (grana) made of individual thylakoids

channel interconnecting thylakoids granum (stack of thylakoids)
Figure 4-17 A chloroplast outer membrane inner membrane stroma thylakoid channel interconnecting thylakoids granum (stack of thylakoids) 1 micrometer 61

Mitochondria extract energy from food molecules, and chloroplasts capture solar energy (continued) Chloroplasts are the sites of photosynthesis (continued) The thylakoid membranes contain the green pigment chlorophyll and other pigments, which capture sunlight and make sugar from CO2 and water (photosynthesis)

Mitochondria extract energy from food molecules, and chloroplasts capture solar energy (continued) Plants use plastids for storage Plastids are found only in plants and photosynthetic protists They are surrounded by a double membrane Plastids are storage containers for various molecules, such as pigments or starch

Figure 4-18 A plastid plastid starch globules 0.5 micrometer 64

4.4 What Are the Major Features of Prokaryotic Cells?
Prokaryotic cells are small and possess specialized surface features Prokaryotic cells have fewer specialized structures within their cytoplasm

Prokaryotic cells are small and possess specialized surface features (continued) Most prokaryotic cells (bacteria) are less than 5 µm long, with a simple internal structure compared to eukaryotic cells They usually have a stiff cell wall Prokaryotic cells can take several shapes Rod-shaped bacilli Spiral-shaped spirilla Spherical cocci

Figure 4-19 Prokaryotic cells are simpler than eukaryotic cells
chromosome (within the nucleoid region) cell wall plasma membrane ribosomes chromosome (within the nucleoid region) capsule Cocci Internal structure pili ribosomes Spirilla food granule prokaryotic flagellum capsule or slime layer cell wall cytoplasm plasma membrane plasmid (DNA) photosynthetic membranes Generalized prokaryotic cell (bacillus) Photosynthetic prokaryote 67

Prokaryotic cells are small and possess specialized surface features (continued) Bacteria secrete polysaccharide coatings called capsules and slime layers outside their cells Capsules and slime layers are similar except capsules are harder to remove Capsules and slime layers assist in the formation of bacteria on surface films Examples include tooth decay, diarrhea, and urinary tract infections Both protect bacteria and keep them from drying out

Prokaryotic cells are small and possess specialized surface features (continued) Pili (meaning hairs) are surface protein projections of the cell walls in some bacteria that further enhance adhesion Attachment pili are short and abundant; they help bacteria adhere to structures Sex pili are few in number and long; one bacterium’s sex pili binds it to a nearby bacterium of the same type

Prokaryotic cells have fewer specialized cytoplasmic structures than do eukaryotic cells In the central region of the cell is an area called the nucleoid, which is separate from the cytoplasm Within the nucleoid is a single, circular chromosome of DNA Small rings of DNA (plasmids) are located in the cytoplasm

Prokaryotic cells have fewer specialized cytoplasmic structures than do eukaryotic cells (continued) Prokaryotic cells have no nuclear membrane or membrane-bound organelles present Some have internal membranes used to capture light The cytoplasm may contain food granules and ribosomes, the latter with a function similar to that of ribosomes in eukaryotic cells

Cell Structure and Function

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