Cell Structure and Function PDF

Chapter 4: Cell Structure and Function 1  Detailed study of the cell began in the 1830s  Cell theory is a unifying concept in biology, states that: 1. All organisms are composed of cells. 2. All cells come only from pr...

Chapter 4: Cell Structure and Function 1  Detailed study of the cell began in the 1830s  Cell theory is a unifying concept in biology, states that: 1. All organisms are composed of cells. 2. All cells come only from preexisting cells. 3. Cells are the smallest structural and functional unit of organisms. 2   Cells range in size from one millimeter down to one micrometer. 0.1 nm 1 nm 10 nm 100 nm 1 m 10 m 100 m 1 mm 1 cm 0.1 m 1 m 10 m 100 m 1 km protein chloroplast plant and mouse rose frog egg animal amino cells acid virus ostrich most bacteria human egg ant egg atom blue whale electron microscope human light microscope human eye  Cells need a large surface area of plasma membrane to adequately exchange materials.  The surface-area-to-volume ratio requires that cells be small. ▪ The surface-area-to-volume ratio requires that cells be small. ▪ Large cells: surface area relative to volume decreases. ▪ Small cells: surface area relative to volume increases. ▪ Volume is living cytoplasm, which demands nutrients and produces wastes ▪ Cells specialized in absorption utilize membrane modifications such as microvilli to greatly increase surface area per unit volume.  There are 2 different types of cells:  Prokaryotic cells which Lack a membrane-bound nucleus.  Eukaryotic cells which has a nucleus.  Prokaryotic cells are structurally smaller and simpler than eukaryotic cells.  Prokaryotic cells are placed in two taxonomic domains: ◦ Bacteria ◦ Archaea ◦ Domains are structurally similar but biochemically different 6 1. Cell Envelope includes: 1. Plasma membrane : lipid bilayer with imbedded and peripheral protein.  Form internal pouches (mesosomes). 2. Cell wall : maintains the shape of the cell and is strengthened by peptidoglycan. 3. Glycocalyx : layer of polysaccharides on the outside of the cell wall.  When this layer is well organized and resistant to removal, it is called capsule.  The glycocalyx protects the bacteria cell from drying out and resists host’s immune system. 7  Cytoplasm: semifluid solution containing water, inorganic and organic molecules, and enzymes. Ribosomes are particles with RNA- and two Inclusion body: stored nutrients for protein-containing subunits that synthesize later use proteins. Mesosome: plasma membrane that nucleoid is the location of a single, circular folds into the cytoplasm and DNA molecule. increases surface area Fimbriae: hairlike bristles that allow Plasma membrane: sheath around cytoplasm adhesion to the surfaces that regulates entrance and exit of molecules Cell wall: covering that supports, shapes, and protects cell Glycocalyx: gel-like coating outside cell wall; if compact, called a capsule; if diffuse, called a slime layer Flagellum: rotating filament present in some bacteria that pushes the cell forward  Cyanobacteria (also called blue-green bacteria) are bacteria that photosynthesize; they lack chloroplasts but have thylakoids containing chlorophyll and other pigments. A. Origin of the Eukaryotic cell  Domain Eukarya includes 4 kingdoms: 1. Protists 2. Fungi 3. Plants 4. Animals  Cells contain: ▪ Membrane-bound nucleus that houses DNA. ▪ Specialized organelles. ▪ Plasma membrane. ▪ Much larger than prokaryotic cells. ▪ Some cells (e.g., plant cells) have a cell wall. 10  B. Structure of Eukaryotic Cells  Eukaryotic cells are compartmentalized: ◦ They contain small structures called organelles.  Perform specific functions  Isolates reactions from others  Two classes of organelles: 1. Endomembrane system:  Organelles that communicate with one another:  Via membrane channels.  Via small vesicles. 2. Energy related organelles  Mitochondria & chloroplasts.  Basically independent & self-sufficient. 11  The cytoskeleton : ◦ is a lattice of protein fibers that maintains the shape of the cell and assists in movement of the organelles.  Some eukaryotic cells (e.g., plant cells): ◦ have a cell wall containing cellulose. ◦ plasmodesmata are channels in a cell wall that allow cytoplasmic strands to extend between adjacent cells. A. Nucleus  The nucleus is the command center of the cell.  The nucleus generally located near the cell center.  The nucleus contain chromatin in a semifluid matrix called nucleoplasm.  The chromatin is a net work of strands that condenses and undergo coiling into rod-like structures called chromosomes just before cell division.  The chromatin contains DNA, protein, and some RNA. 13  The nucleolus is a dark region of chromatin inside the nucleus; it is the site where ribosomes are produced.  The nucleus is separated from the cytoplasm by the nuclear envelope, which contains nuclear pores to permit passage of substances (e.g., ribosomal subunits, messenger RNA, proteins, etc.) in and out of the nucleus. 4.4 The Nucleus and Ribosomes nuclear envelope nucleolus Nuclear envelope: nuclear inner membrane pore outer membrane chromatin nucleoplasm nuclear pore phospholipid (Bottom): Courtesy Ron Milligan/Scripps Research Institute; (Top right): Courtesy E.G. Pollock 15 B. Ribosomes  Ribosomes are particles where protein synthesis occurs.  Composed of rRNA and proteins.  Consists of a large subunit and a small subunit  In eukaryotic cells may be located: ◦ On the endoplasmic reticulum (thereby making it “rough”). ◦ Free in the cytoplasm, either singly or in groups, called polyribosomes. ◦ Ribosomes receive messenger RNA (mRNA) from the nucleus. 16 Plasma membrane: outer surface that regulates entrance and exit of molecules protein phospholipid Nucleus: command center of cell Nuclear envelope: double Cytoskeleton: maintains membrane with nuclear pores cell shape and assists movement that encloses nucleus of cell parts: Chromatin: diffuse threads containing DNA and protein Microtubules: protein Nucleolus: region that produces cylinders that move subunits of ribosomes organelles Endoplasmic reticulum: Intermediate filaments: protein and lipid metabolism protein fibers that provide Rough ER: studded with stability of shape ribosomes that synthesize Actin filaments: protein proteins fibers that play a role in Smooth ER: lacks change of shape ribosomes, synthesizes lipid molecules Centrioles*: short Peroxisome: vesicle cylinders of microtubules that is involved in of unknown function fatty acid metabolism Centrosome: microtubule Ribosomes: organizing center that particles that carry contains a pair of centrioles out protein synthesis Lysosome*: vesicle that Polyribosome: string of digests macromolecules ribosomes simultaneously and even cell parts synthesizing same protein Vesicle: small membrane- bounded sac that stores and transports substances Mitochondrion: organelle Cytoplasm: semifluid that carries out cellular respiration, matrix outside nucleus producing ATP molecules that contains organelles Golgi apparatus: processes, packages, *not in plant cells and secretes modified proteins 17 Nucleus: command center of cell Central vacuole*: large, fluid-filled Nuclear envelope: double membrane with sac that stores metabolites and nuclear pores that encloses nucleus helps maintain turgor pressure Nucleolus: produces subunits of ribosomes Chromatin: diffuse threads containing Cell wall of adjacent cell DNA and protein Nuclear pore: permits passage of Middle lamella: proteins into nucleus and ribosomal cements together the subunits out of nucleus primary cell walls of Ribosomes: carry adjacent plant cells out protein synthesis Chloroplast*: carries Centrosome: out photosynthesis, microtubule organizing producing sugars center (lacks centrioles) Granum*: a stack Endoplasmic of chlorophyll-containing reticulum: protein thylakoids and lipid metabolism in a chloroplast Rough ER: studded Mitochondrion: organelle with ribosomes that that carries out cellular synthesize proteins respiration, producing ATP molecules Smooth ER: lacks ribosomes, synthesizes Microtubules: protein cylinders lipid molecules that aid movement of organelles Peroxisome: vesicle that Actin filaments: protein fibers is involved in fatty acid that play a role in movement of metabolism cell and organelles Golgi apparatus: processes, Plasma membrane: surrounds packages, and secretes cytoplasm, and regulates entrance modified proteins and exit of molecules Cytoplasm: semifluid matrix outside Cell wall*: outer surface that shapes, nucleus that contains organelles supports, and protects cell *not in animal cells 18 A. The Endomembrane System  Series of intracellular membranes that compartmentalize the cell so that enzymatic reactions are restricted to specific regions within cell.  Consists of: ◦ Nuclear envelope ◦ Membranes of endoplasmic reticulum ◦ Golgi apparatus ◦ Vesicles  Several types  Transport materials between organelles of system 19 B. The Endoplasmic Reticulum  A system of membrane channels and saccules (flattened vesicles) continuous with the outer membrane of the nuclear envelope  Rough ER ◦ Studded with ribosomes on cytoplasmic side  Synthesizes proteins  Modifies and processes proteins ◦ Forms vesicles that transport molecules to other parts of the cells, notably the Golgi apparatus. 20  Smooth ER ◦ No ribosomes ◦ Synthesis of lipids ◦ Site of various synthetic processes, detoxification, and storage ◦ Forms vesicles that transport molecules to other parts of the cells, notably the Golgi apparatus. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ribosomes nuclear envelope rough endoplasmic reticulum smooth endoplasmic reticulum 0.08 m © R. Bolender & D. Fawcett/Visuals Unlimited 22 C. Golgi Apparatus secretion  Consists of a stack of slightly curved saccules.  It receives protein-filled vesicles that bud from the rough ER and lipid- filled vesicles from the smooth ER.  Enzymes within the Golgi apparatus transport vesicle modify the carbohydrates that were transport vesicle placed on proteins in the ER.  Within Golgi apparatus proteins and lipids are sorted and packaged.  Vesicles formed from the membrane of the outer face of the Golgi apparatus move to different locations in a cell; at the plasma membrane they discharge their contents as secretions. 23 D. Lysosomes  Membrane-bound vesicles (not in plants) ◦ Produced by the Golgi apparatus ◦ Contain powerful digestive enzymes and are highly acidic ◦ Digestion of large molecules that enter a cell by vesicle formation; lysosomes fuse with vesicles and digest the contents of the vesicle. ◦ White blood cells that engulf bacteria use lysosomes to digest the bacteria. ◦ Autodigestion occurs when lysosomes digest parts of cells. ◦ Participate in apoptosis, or programmed cell death, a normal part of development. 24 25  secretion plasma membrane incoming vesicle secretory vesicle brings substances into the fuses with the plasma cell that are digested when membrane as secretion the vesicle fuses with a occurs lysosome enzyme Golgi apparatus modifies lipids and proteins lysosome from the ER; sorts them contains digestive enzymes and packages them in that break down worn-out vesicles cell parts or substances entering the cell at the plasma membrane protein transport vesicle transport vesicle shuttles proteins to shuttles lipids to various various locations such as locations such as the the Golgi apparatus Golgi apparatus lipid rough endoplasmic smooth endoplasmic reticulum reticulum synthesizes proteins and synthesizes lipids and packages them in vesicles; also performs various vesicles commonly go to other functions the Golgi apparatus ribosome Nucleus 26  Peroxisomes and the other vacuoles of cells do not communicate with the organelles of the endomembrane system, and therefore are not part of it.  They are membrane-bounded vesicles that enclose enzymes  However: ◦ All peroxisomes contain enzymes whose actions result in the production of hydrogen peroxide H2O2.  Toxic  Broken down to water and oxygen by an enzyme called catalase. 28  Membranous sacs that are larger than vesicles ◦ Store materials that occur in excess ◦ contractile vacuole: in some protists rid the cell of excess water). ◦ Digestive vacuoles digest nutrients.  Plants cells typically have a central vacuole ◦ Up to 90% volume of some cells ◦ Functions in:  Storage of water, nutrients, pigments, and waste products  Development of turgor pressure  Degrades organelles as the cell ages. 29  100 nm © Newcomb/Wergin/Biological Photo Service 30  Chloroplast and mitochondria are the two eukaryotic membranous organelles that specialized in converting energy to a form that can be used by the cell.  Photosynthesis in chloroplasts:  Solar energy + CO2 + H2O carbohydrate + O2  Plants, algae and cyanobacteria are capable of carrying photosynthesis.  Only plants and algae (eukaryotes) have chloroplasts.  Cellular respiration is carried out by mitochondria in which carbohydrates-derived products are broken down:  carbohydrate + O2 energy (ATP) + CO2 + H2O  Membranous organelles that serve as the site of photosynthesis.  They have a three-membrane system: 1. Bound by a double membrane. 2. An inner (third) membrane forms flattened disc-like sacs called thylakoids: one stack is called granum. Chlorphyll and enzymes in chloroplast. Chloroplasts have both their own DNA and ribosomes, supporting the endosymbiotic hypothesis. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. 500 nm outer thylakoid membrane grana space stroma thylakoid membrane double inner membrane membrane b. a: Courtesy Herbert W. Israel, Cornell University  Power houses of the cell (produce ATP).  Smaller than chloroplast.  Contain ribosomes and their own DNA (endosymbiotic theory).  Surrounded by a double membrane  Inner membrane surrounds the matrix and is convoluted (folds) to form cristae.  Matrix – Inner semifluid containing respiratory enzymes  Break down carbohydrates  Involved in cellular respiration  Produce most of ATP utilized by the cell Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. 200 nm outer membrane cristae matrix double inner membrane membrane b. a: Courtesy Dr. Keith Porter The cytoskeleton is a network of connected filaments and tubules; it extends from the nucleus to the plasma membrane in eukaryotes. Maintains cell shape Assists in movement of cell and organelles Three types of macromolecular fibers: 1. Actin Filaments 2. Intermediate Filaments 3. Microtubules Assemble and disassemble as needed.  A. Actin filaments :  are long, thin fibers (about 7 nm in diameter) that occur in bundles or meshlike networks.  The actin filament consists of two chains of globular actin monomers twisted about one another.  Structural role : ◦ microvilli in intestinal cells. ◦ Intracellular traffic control. ◦ For moving stuff around within cell ◦ Cytoplasmic streaming  Pinch mother cell in two after animal mitosis.  Important component in muscle contraction (the other is myosin). 37  actin filament ATP ADP + P myosin molecules tail head membrane 38  B. Intermediate Filaments:  In size 8–11 nm in diameter between actin filaments and microtubules  Rope-like assembly of fibrous polypeptides  Vary in nature ◦ From tissue to tissue  Functions: ◦ Support nuclear envelope ◦ Cell-cell junctions, like those holding skin cells tightly together 39  C. Microtubules:  Are Hollow cylinders made of two globular proteins called a and b tubulin  Spontaneous pairing of a and b tubulin molecules form structures called dimers  Dimers then arrange themselves into tubular spirals of 13 dimers.  help maintain the shape of cells and acting as tracks along which organelles move. 40  ATP vesicle kinesin kinesin receptor vesicle moves, not microtubule 41  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. actin subunit Chara a. Actin filaments fibrous subunits peacock b. Intermediate filaments tubulin dimer chameleon c. Microtubules a(Actin): © M. Schliwa/Visuals Unlimited; b, c(Intermediate, Microtubules): © K.G. Murti/Visuals Unlimited; a(Chara): The McGraw-Hill Companies, Inc./photo by 42 Dennis Strete and Darrell Vodopich; b(Peacock): © Vol. 86/Corbis; c(Chameleon): © Photodisc/Vol. 6/Getty Images D. Centrioles:  Are short, hollow cylinders ◦ With a ring pattern (9 + 0) of microtubule ◦ One pair per animal cell ◦ Located in centrosome of animal cells ◦ Oriented at right angles to each other ◦ Separate during mitosis to determine plane of division  Plant and fungal cells have the equivalent of a centrosome, but they do not contain centrioles. 43  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. empty center of centriole one microtubule triplet E. Cilia and Flagella: 1. Cilia are hair-like projections from cell surface that aid in cell movement which are found in for example Paramecium; lining of human upper respiratory tract. 45 2. Flagella are longer, usually fewer, projections that move in whip-like fashion (e.g., sperm cells). 3. Both have similar construction but differ from prokaryotic flagella. a. Membrane-bounded cylinders enclose a matrix containing a cylinder of nine pairs of microtubules encircling two single microtubules (9 + 2 pattern of microtubules).  In eukaryotes, cilia are much shorter than flagella: ◦ Cilia move in coordinated waves like oars. ◦ Flagella move like a propeller.  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. outer Flagellum microtubule doublet radial spoke central shaft The shaft of the microtubules flagellum has a ring of nine microtubule doublets anchored dynein to a central pair of side arm microtubules. 25 nm Flagellum cross section The side arms dynein Sperm of each doublet side arms plasma are composed triplets membrane of dynein, a motor molecule. Basal body ATP In the presence of ATP, the dynein side arms reach out to their neighbors, The basal body of a flagellum has and bending occurs. 100 nm a ring of nine microtubule triplets Basal body cross section with no central microtubules. (Flagellum, Basal body): © William L. Dentler/Biological Photo Service 47