Cell Structure and Function

Cell Structure and Function
Chapter 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?

Three principles comprise the cell theory
4.1 What Is the Cell Theory? 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?
Cell function limits cell size Most cells range in size from about 1 to 100 micrometers in diameter

visible with conventional
Relative Sizes Size 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 proteins visible with special electron microscope 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 Fig. 4-1 0.1 nm atoms

Cell function limits cell size (continued) Cells need to exchange nutrients and wastes with the environment No part of the cell can be too far away from the external environment

All cells share common features 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

The Plasma Membrane carbo- extracellular fluid (outside) hydrate
glycoprotein A phospholipid bilayer helps to isolate the cell's contents Proteins help the cell communicate with its environment cholesterol membrane protein channel protein cytoskeleton cytoplasm (inside) Fig. 4-2

All cells share common features (continued) 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 (cytoplasmic fluid) contains water, salts, and organic molecules Most of the cell’s metabolic activities occur in the cell cytoplasm

A Generalized Animal Cell
microfilaments nuclear envelope nuclear pore nucleus chromatin (DNA) cytoplasmic fluid nucleolus micro- (cytoskeleton) tubules flagellum basal body rough endoplasmic reticulum vesicle intermediate filaments (cytoskeleton) cytoplasm Golgi apparatus centriole ribosomes on rough ER polyribosome lysosome smooth endoplasmic reticulum exocytosis of material from the cell mitochondrion plasma membrane Fig. 4-3 free ribosome

A Generalized Plant Cell
nuclear envelope ribosomes nuclear pore intermediate filaments (cytoskeleton) nucleus chromatin nucleolus microtubules (cytoskeleton) cell walls of adjoining plant cells chloroplast cytoplasm rough endoplasmic reticulum lysosome smooth endoplasmic reticulum Golgi apparatus central vacuole vesicle mitochondrion cell wall plasma membrane plasmodesmata Fig. 4-4 cytoplasmic fluid plastid free ribosome

All cells share common features (continued) 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

All cells share common features (continued) All cells obtain raw materials and energy from their environment The building blocks of biological molecules—such as carbon, hydrogen, oxygen, nitrogen, and phosphorus, as well as a variety of minerals—come from the environment

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

4.3 What Are the Major Features of Eukaryotic Cells?
Eukaryotic cells are usually larger than prokaryotic cells 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

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 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) 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

The Cytoskeleton Fig. 4-5 intermediate filaments microtubules
microfilaments (a) Cytoskeleton microtubules (red) nucleus microfilaments (blue) Fig. 4-5 (b) Light micrograph showing the cytoskeleton

Table 4-2

The cytoskeleton performs the following important functions: Maintaining and changing cell shape Providing for cell movement Providing for organelle movement Facilitating cell division

Cilia and flagella move the cell through fluid or move fluid past the cell Both cilia and flagella are slender extensions of the plasma membrane They arise from a basal body, which anchors them to the plasma membrane Basal bodies are derived from centrioles

Cilia and Flagella central pair of protein microtubules “arms”
section of cilium 0.1 micrometer Paramecium cilium plasma membrane basal body Fig. 4-6

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

How Cilia and Flagella Move
cilia lining trachea propulsion of fluid (a) Cilium power stroke return stroke plasma membrane direction of locomotion propulsion of fluid flagellum of human sperm surface of human egg cell (b) Flagellum continuous propulsion Fig. 4-7

The nucleus is the control center of the eukaryotic cell The nucleus is an organelle that contains three major parts Nuclear envelope Chromatin Nucleolus

The nucleus is the control center of the eukaryotic cell (continued) 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 is regulated by gatekeeper proteins called the nuclear pore complex that line each nuclear pore

The Nucleus Fig. 4-8 nuclear envelope nuclear pores nucleolus
ribosomes nucleus chromatin nuclear pores with nuclear pore complex (a) The nucleus (b) Nucleus of a yeast cell Fig. 4-8

The nucleus is the control center of the eukaryotic cell (continued) The nucleus contains chromatin, which consists of DNA and proteins 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 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

Chromosomes chromatin chromosome Fig. 4-9

The nucleus is the control center of the eukaryotic cell (continued) The nucleolus is the site of ribosome 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

Ribosomes are the site of protein synthesis in the cell
mRNA polyribosome growing protein Fig. 4-10 amino acid

The eukaryotic cytoplasm includes an elaborate system of membranes Vesicles are membranous sacs that transport substances among the separate regions of the membrane system The cell’s membrane system includes the plasma membrane, nuclear membrane, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and vacuoles

The eukaryotic cytoplasm includes an elaborate system of membranes (continued) The endoplasmic reticulum (ER) is a series of interconnected membranes that form a labyrinth of interconnected flattened sacs and channels within the cytoplasm All the proteins and phospholipids of cell membranes are synthesized in the ER

Endoplasmic Reticulum
smooth ER ribosomes rough ER smooth ER rough ER vesicles (a) Endoplasmic reticulum may be rough or smooth (b) Smooth and rough ER Fig. 4-11

The eukaryotic cytoplasm includes an elaborate system of membranes (continued) There are two forms of ER: Smooth endoplasmic reticulum has no ribosomes, detoxifies drugs, and synthesizes lipids like steroid hormones made from cholesterol Rough endoplasmic reticulum is studded with ribosomes and produces proteins destined for other membranes or for secretion

The eukaryotic cytoplasm includes an elaborate system of membranes (continued) The Golgi apparatus sorts, chemically alters, 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 It synthesizes some polysaccharides used in plant cell walls, such as cellulose and pectin

The Golgi apparatus sorts, chemically alters, 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

The Golgi Apparatus Fig. 4-12 Protein-carrying vesicles from the ER
merge with the Golgi apparatus Golgi apparatus Vesicles carrying modified protein leave the Golgi apparatus Fig. 4-12

The eukaryotic cytoplasm includes an elaborate system of membranes (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

Author Animation: Membrane System

Author Animation: Exocytosis

A Protein Is Manufactured and Exported
(extracellular fluid) 5 Vesicles merge with the plasma membrane and release antibodies into the extracellular fluid (cytoplasm) 4 Completed glycoprotein antibodies are packaged into vesicles on the opposite side of the Golgi apparatus vesicles Golgi apparatus 3 Vesicles fuse with the Golgi apparatus, and carbohydrates are added as the protein passes through the compartments 2 The protein is packaged into vesicles and travels to the Golgi apparatus forming vesicle 1 Antibody protein is synthesized on ribosomes and is transported into channels of the rough ER Fig. 4-13

The eukaryotic cytoplasm includes an elaborate system of membranes (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 as lysosomes A lysosome fuses with a food vacuole and digests food into basic nutrients

Author Animation: Phagocytosis

Formation and Function of Lysosomes and Food Vacuoles
(extracellular fluid) food A lysosome fuses with a food vacuole, and the enzymes digest the food 5 (cytoplasm) food vacuoles 4 The enzymes are packaged into lysosomes, which bud from the Golgi apparatus lysosome The Golgi apparatus modifies the enzymes as they pass through its compartments 3 Golgi apparatus 2 The enzymes are packaged into vesicles and travel to the Golgi apparatus digestive enzymes 1 Digestive enzymes are synthesized on ribosomes and travel through the rough ER Fig. 4-14

The eukaryotic cytoplasm includes an elaborate system of membranes (continued) Membrane is exchanged throughout the cell Membrane proteins and lipids are made in ER, travel through Golgi, and replenish or enlarge organelle and plasma membranes

Vacuoles serve many functions, including water regulation, support, and storage Most cells contain one or more vacuoles, which are sacs of cell membrane filled with fluid containing various molecules 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 Figure: 19-2 part a Title: Viral structure and replication part a Caption: (a) A cross section of the virus that causes AIDS. Inside, genetic material is surrounded by a protein coat and molecules of reverse transcriptase, an enzyme that catalyzes the transcription of DNA from the viral RNA template after the virus enters the host cell. This virus is among those that also have an outer envelope that is formed from the host cell's plasma membrane. Spikes made of glycoprotein (protein and carbohydrate) project from the envelope and help the virus attach to its host cell.

Contractile Vacuoles Fig. 4-15 contractile vacuole
Water enters the collecting ducts and fills the central reservoir (a) Paramecium collecting ducts central reservoir pore The reservoir contracts, expelling water through the pore Fig. 4-15 (b) Contractile vacuole

Functions of vacuoles Plant central vacuoles, which occupy three-quarters or more of the volume of many plant cells, are used in several ways: To maintain water balance To store hazardous wastes, nutrients, or pigments To provide turgor pressure on the cytoplasm to keep cells rigid Figure: 19-2 part a Title: Viral structure and replication part a Caption: (a) A cross section of the virus that causes AIDS. Inside, genetic material is surrounded by a protein coat and molecules of reverse transcriptase, an enzyme that catalyzes the transcription of DNA from the viral RNA template after the virus enters the host cell. This virus is among those that also have an outer envelope that is formed from the host cell's plasma membrane. Spikes made of glycoprotein (protein and carbohydrate) project from the envelope and help the virus attach to its host cell.

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)

Evidence for 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

A Mitochondrion outer membrane inner membrane intermembrane space
matrix cristae 0.2 micrometer Fig. 4-16

Mitochondria are round, oval, or tubular sacs of double membranes They function as the “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

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

A Chloroplast outer membrane inner membrane stroma thylakoid channel
interconnecting thylakoids granum (stack of thylakoids) 1 micrometer Fig. 4-17

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)

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

A Plastid plastid starch globules 0.5 micrometer Fig. 4-18

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

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 Spiral-shaped Spherical

Prokaryotic Cells Are Simpler Than Eukaryotic Cells
chromosome (nucleoid region) cell wall plasma membrane ribosomes capsule chromosome (nucleoid region) (d) Internal structure pili (c) Cocci ribosomes food granule prokaryotic flagellum (b) Spirilla capsule or slime layer cell wall plasma membrane cytoplasm plasmid (DNA) photosynthetic membranes (a) Generalized prokaryotic cell (bacillus) (e) Photosynthetic prokaryote Fig. 4-19

Some bacteria and archaea are propelled by flagella Infectious bacteria may have polysaccharide adhesive capsules and slime layers on their surfaces Pili are protein projections in some bacteria that further enhance adhesion

Prokaryotic cells (continued) 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 (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 similar function as that of ribosomes in eukaryotic cells

Cell Structure and Function

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