Sinh học - Chapter 6: A tour of the cell

A Tour of the CellChapter 6Overview: The Fundamental Units of LifeAll organisms are made of cellsThe cell is the simplest collection of matter that can be aliveCell structure is correlated to cellular functionAll cells are related by their descent from earlier cells© 2011 Pearson Education, Inc.Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functionsThe basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryoticOnly organisms of the domains Bacteria and Archaea consist of prokaryotic cellsProtists, fungi, animals, and plants all consist of eukaryotic cells© 2011 Pearson Education, Inc.Comparing Prokaryotic and Eukaryotic CellsBasic features of all cells Plasma membraneSemifluid substance called cytosolChromosomes (carry genes)Ribosomes (make proteins)© 2011 Pearson Education, Inc.Prokaryotic cells are characterized by havingNo nucleusDNA in an unbound region called the nucleoidNo membrane-bound organellesCytoplasm bound by the plasma membrane© 2011 Pearson Education, Inc.FimbriaeBacterialchromosomeA typicalrod-shapedbacterium(a)NucleoidRibosomesPlasmamembraneCell wallCapsuleFlagellaA thin sectionthrough thebacterium Bacilluscoagulans (TEM)(b)0.5 mFigure 6.5Eukaryotic cells are characterized by havingDNA in a nucleus that is bounded by a membranous nuclear envelopeMembrane-bound organellesCytoplasm in the region between the plasma membrane and nucleusEukaryotic cells are generally much larger than prokaryotic cells© 2011 Pearson Education, Inc.The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cellThe general structure of a biological membrane is a double layer of phospholipids© 2011 Pearson Education, Inc.Figure 6.6Outside of cellInside of cell0.1 m(a)TEM of a plasmamembraneHydrophilicregionHydrophobicregionHydrophilicregionCarbohydrate side chainsProteinsPhospholipid(b) Structure of the plasma membraneMetabolic requirements set upper limits on the size of cells The surface area to volume ratio of a cell is criticalAs the surface area increases by a factor of n2, the volume increases by a factor of n3Small cells have a greater surface area relative to volume© 2011 Pearson Education, Inc.Surface area increases whiletotal volume remains constantTotal surface area[sum of the surface areas(height  width) of all boxsides  number of boxes]Total volume[height  width  length number of boxes]Surface-to-volume(S-to-V) ratio[surface area  volume]156150750112512511.266Figure 6.7A Panoramic View of the Eukaryotic CellA eukaryotic cell has internal membranes that partition the cell into organellesPlant and animal cells have most of the same organelles© 2011 Pearson Education, Inc.Figure 6.8aENDOPLASMIC RETICULUM (ER)RoughERSmoothERNuclearenvelopeNucleolusChromatinPlasmamembraneRibosomesGolgi apparatusLysosomeMitochondrionPeroxisomeMicrovilliMicrotubulesIntermediate filamentsMicrofilamentsCentrosomeCYTOSKELETON:FlagellumNUCLEUSFigure 6.8bAnimal CellsCellNucleusNucleolusHuman cells from liningof uterus (colorized TEM)Yeast cells budding(colorized SEM)10 mFungal Cells5 mParentcellBuds1 mCell wallVacuoleNucleusMitochondrionA single yeast cell(colorized TEM)NUCLEUSNuclearenvelopeNucleolusChromatinGolgiapparatusMitochondrionPeroxisomePlasma membraneCell wallWall of adjacent cellPlasmodesmataChloroplastMicrotubulesIntermediatefilamentsMicrofilamentsCYTOSKELETONCentral vacuoleRibosomesSmoothendoplasmicreticulumRoughendoplasmicreticulumFigure 6.8cConcept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomesThe nucleus contains most of the DNA in a eukaryotic cellRibosomes use the information from the DNA to make proteins© 2011 Pearson Education, Inc.The Nucleus: Information CentralThe nucleus contains most of the cell’s genes and is usually the most conspicuous organelleThe nuclear envelope encloses the nucleus, separating it from the cytoplasmThe nuclear membrane is a double membrane; each membrane consists of a lipid bilayer© 2011 Pearson Education, Inc.NucleusRough ERNucleolusChromatinNuclear envelope:Inner membraneOuter membraneNuclear poreChromatinRibosomePorecomplexClose-upof nuclearenvelopeFigure 6.9aPores regulate the entry and exit of molecules from the nucleusThe shape of the nucleus is maintained by the nuclear lamina, which is composed of protein© 2011 Pearson Education, Inc.In the nucleus, DNA is organized into discrete units called chromosomesEach chromosome is composed of a single DNA molecule associated with proteins The DNA and proteins of chromosomes are together called chromatinChromatin condenses to form discrete chromosomes as a cell prepares to divideThe nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis© 2011 Pearson Education, Inc.Ribosomes: Protein FactoriesRibosomes are particles made of ribosomal RNA and proteinRibosomes carry out protein synthesis in two locationsIn the cytosol (free ribosomes)On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes)© 2011 Pearson Education, Inc.Figure 6.100.25 mFree ribosomes in cytosolEndoplasmic reticulum (ER)Ribosomes bound to ERLargesubunitSmallsubunitDiagram of a ribosomeTEM showing ER andribosomesConcept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cellComponents of the endomembrane systemNuclear envelopeEndoplasmic reticulumGolgi apparatusLysosomesVacuolesPlasma membraneThese components are either continuous or connected via transfer by vesicles© 2011 Pearson Education, Inc.The Endoplasmic Reticulum: Biosynthetic FactoryThe endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cellsThe ER membrane is continuous with the nuclear envelopeThere are two distinct regions of ERSmooth ER, which lacks ribosomesRough ER, surface is studded with ribosomes© 2011 Pearson Education, Inc.Figure 6.11Smooth ERRough ERER lumenCisternaeRibosomesSmooth ERTransport vesicleTransitional ERRough ER200 nmNuclearenvelopeFunctions of Smooth ERThe smooth ERSynthesizes lipidsMetabolizes carbohydratesDetoxifies drugs and poisonsStores calcium ions© 2011 Pearson Education, Inc.Functions of Rough ERThe rough ERHas bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates)Distributes transport vesicles, proteins surrounded by membranesIs a membrane factory for the cell© 2011 Pearson Education, Inc.The Golgi apparatus consists of flattened membranous sacs called cisternaeFunctions of the Golgi apparatusModifies products of the ERManufactures certain macromoleculesSorts and packages materials into transport vesiclesThe Golgi Apparatus: Shipping and Receiving Center© 2011 Pearson Education, Inc.Figure 6.12cis face(“receiving” side ofGolgi apparatus)trans face(“shipping” side ofGolgi apparatus)0.1 mTEM of Golgi apparatusCisternaeLysosomes: Digestive CompartmentsA lysosome is a membranous sac of hydrolytic enzymes that can digest macromoleculesLysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acidsLysosomal enzymes work best in the acidic environment inside the lysosome© 2011 Pearson Education, Inc.Some types of cell can engulf another cell by phagocytosis; this forms a food vacuoleA lysosome fuses with the food vacuole and digests the moleculesLysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy© 2011 Pearson Education, Inc.Figure 6.13NucleusLysosome1 mDigestiveenzymesDigestionFood vacuoleLysosomePlasma membrane(a) PhagocytosisVesicle containingtwo damagedorganelles1 mMitochondrionfragmentPeroxisomefragment(b) AutophagyPeroxisomeVesicleMitochondrionLysosomeDigestionVacuoles: Diverse Maintenance CompartmentsA plant cell or fungal cell may have one or several vacuoles, derived from endoplasmic reticulum and Golgi apparatus© 2011 Pearson Education, Inc.Food vacuoles are formed by phagocytosisContractile vacuoles, found in many freshwater protists, pump excess water out of cellsCentral vacuoles, found in many mature plant cells, hold organic compounds and water© 2011 Pearson Education, Inc.Figure 6.14Central vacuoleCytosolNucleusCell wallChloroplastCentralvacuole5 mThe Endomembrane System: A ReviewThe endomembrane system is a complex and dynamic player in the cell’s compartmental organization© 2011 Pearson Education, Inc.Figure 6.15-3Smooth ERNucleusRough ERPlasmamembranecis Golgitrans GolgiConcept 6.5: Mitochondria and chloroplasts change energy from one form to anotherMitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATPChloroplasts, found in plants and algae, are the sites of photosynthesisPeroxisomes are oxidative organelles© 2011 Pearson Education, Inc.Mitochondria and chloroplasts have similarities with bacteria Enveloped by a double membraneContain free ribosomes and circular DNA moleculesGrow and reproduce somewhat independently in cells© 2011 Pearson Education, Inc.The Evolutionary Origins of Mitochondria and ChloroplastsThe Endosymbiont theory An early ancestor of eukaryotic cells engulfed a nonphotosynthetic prokaryotic cell, which formed an endosymbiont relationship with its hostThe host cell and endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrionAt least one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts© 2011 Pearson Education, Inc.NucleusEndoplasmicreticulumNuclear envelopeAncestor ofeukaryotic cells(host cell)Engulfing of oxygen-using nonphotosyntheticprokaryote, whichbecomes a mitochondrionMitochondrionNonphotosyntheticeukaryoteMitochondrionAt leastone cellPhotosynthetic eukaryote Engulfing ofphotosyntheticprokaryoteChloroplastFigure 6.16Mitochondria: Chemical Energy ConversionMitochondria are in nearly all eukaryotic cellsThey have a smooth outer membrane and an inner membrane folded into cristaeThe inner membrane creates two compartments: intermembrane space and mitochondrial matrixSome metabolic steps of cellular respiration are catalyzed in the mitochondrial matrixCristae present a large surface area for enzymes that synthesize ATP© 2011 Pearson Education, Inc.Figure 6.17aIntermembrane spaceOuterDNAInnermembraneCristaeMatrixFreeribosomesin themitochondrialmatrix(a) Diagram and TEM of mitochondrion0.1 mmembraneChloroplasts: Capture of Light EnergyChloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesisChloroplasts are found in leaves and other green organs of plants and in algae© 2011 Pearson Education, Inc.Chloroplast structure includesThylakoids, membranous sacs, stacked to form a granumStroma, the internal fluidThe chloroplast is one of a group of plant organelles, called plastids© 2011 Pearson Education, Inc.Figure 6.18aRibosomesStromaInner and outermembranesGranum1 mIntermembrane spaceThylakoid(a) Diagram and TEM of chloroplastDNAPeroxisomes: OxidationPeroxisomes are specialized metabolic compartments bounded by a single membranePeroxisomes produce hydrogen peroxide and convert it to waterPeroxisomes perform reactions with many different functionsHow peroxisomes are related to other organelles is still unknown© 2011 Pearson Education, Inc.Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cellThe cytoskeleton is a network of fibers extending throughout the cytoplasmIt organizes the cell’s structures and activities, anchoring many organellesIt is composed of three types of molecular structuresMicrotubulesMicrofilamentsIntermediate filaments© 2011 Pearson Education, Inc.Roles of the Cytoskeleton: Support and MotilityThe cytoskeleton helps to support the cell and maintain its shapeIt interacts with motor proteins to produce motilityInside the cell, vesicles can travel along “monorails” provided by the cytoskeletonRecent evidence suggests that the cytoskeleton may help regulate biochemical activities© 2011 Pearson Education, Inc.Figure 6.21ATPVesicle(a)Motor protein(ATP powered)Microtubuleof cytoskeletonReceptor formotor protein0.25 m VesiclesMicrotubule(b)Components of the CytoskeletonThree main types of fibers make up the cytoskeletonMicrotubules are the thickest of the three components of the cytoskeletonMicrofilaments, also called actin filaments, are the thinnest componentsIntermediate filaments are fibers with diameters in a middle range© 2011 Pearson Education, Inc.Column of tubulin dimersTubulin dimer25 nmActin subunit7 nmKeratin proteins812 nmFibrous subunit (keratinscoiled together)10 m10 m5 mTable 6.1MicrotubulesMicrotubules are hollow rods about 25 nm in diameter and about 200 nm to 25 microns longFunctions of microtubulesShaping the cellGuiding movement of organellesSeparating chromosomes during cell division© 2011 Pearson Education, Inc. Centrosomes and CentriolesIn many cells, microtubules grow out from a centrosome near the nucleusThe centrosome is a “microtubule-organizing center”In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring© 2011 Pearson Education, Inc.CentrosomeLongitudinalsection ofone centrioleCentriolesMicrotubule0.25 mMicrotubulesCross sectionof the other centrioleFigure 6.22 Cilia and FlagellaMicrotubules control the beating of cilia and flagella, locomotor appendages of some cellsCilia and flagella differ in their beating patterns© 2011 Pearson Education, Inc.Direction of swimming(b) Motion of ciliaDirection of organism’s movementPower stroke Recovery stroke(a) Motion of flagella5 m15 mFigure 6.23Cilia and flagella share a common structureA core of microtubules sheathed by the plasma membraneA basal body that anchors the cilium or flagellumA motor protein called dynein, which drives the bending movements of a cilium or flagellum© 2011 Pearson Education, Inc.Figure 6.24ba0.1 m(b)Cross section ofmotile ciliumOuter microtubuledoubletDynein proteinsCentralmicrotubuleRadialspokeCross-linkingproteins betweenouter doubletsMicrofilaments (Actin Filaments)Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunitsThe structural role of microfilaments is to bear tension, resisting pulling forces within the cellThey form a 3-D network called the cortex just inside the plasma membrane to help support the cell’s shapeBundles of microfilaments make up the core of microvilli of intestinal cells© 2011 Pearson Education, Inc.Microfilaments that function in cellular motility contain the protein myosin in addition to actinIn muscle cells, thousands of actin filaments are arranged parallel to one anotherThicker filaments composed of myosin interdigitate with the thinner actin fibers© 2011 Pearson Education, Inc.Figure 6.27Muscle cellActinfilamentMyosinMyosinfilamenthead(a) Myosin motors in muscle cell contraction0.5 m100 mCortex (outer cytoplasm):gel with actin networkInner cytoplasm: solwith actin subunits(b) Amoeboid movementExtendingpseudopodium30 m(c) Cytoplasmic streaming in plant cellsChloroplastLocalized contraction brought about by actin and myosin also drives amoeboid movementPseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments© 2011 Pearson Education, Inc.Cytoplasmic streaming is a circular flow of cytoplasm within cellsThis streaming speeds distribution of materials within the cellIn plant cells, actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming© 2011 Pearson Education, Inc.Intermediate FilamentsIntermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubulesThey support cell shape and fix organelles in placeIntermediate filaments are more permanent cytoskeleton fixtures than the other two classes© 2011 Pearson Education, Inc.Concept 6.7: Extracellular components and connections between cells help coordinate cellular activitiesMost cells synthesize and secrete materials that are external to the plasma membraneThese extracellular structures includeCell walls of plantsThe extracellular matrix (ECM) of animal cellsIntercellular junctions© 2011 Pearson Education, Inc.Cell Walls of PlantsThe cell wall is an extracellular structure that distinguishes plant cells from animal cellsProkaryotes, fungi, and some protists also have cell wallsThe cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of waterPlant cell walls are made of cellulose fibers embedded in other polysaccharides and protein© 2011 Pearson Education, Inc.Secondarycell wallPrimarycell wallMiddlelamellaCentral vacuoleCytosolPlasma membranePlant cell wallsPlasmodesmata1 mFigure 6.28The Extracellular Matrix (ECM) of Animal CellsAnimal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM)The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectinECM proteins bind to receptor proteins in the plasma membrane called integrins© 2011 Pearson Education, Inc.Figure 6.30EXTRACELLULAR FLUIDCollagenFibronectinPlasmamembraneMicro-filamentsCYTOPLASMIntegrinsProteoglycancomplexPolysaccharidemoleculeCarbo-hydratesCoreproteinProteoglycanmoleculeProteoglycan complexFunctions of the ECMSupportAdhesionMovementRegulation© 2011 Pearson Education, Inc.Cell JunctionsNeighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contactIntercellular junctions facilitate this contactThere are several types of intercellular junctionsPlasmodesmataTight junctionsDesmosomesGap junctions© 2011 Pearson Education, Inc.Plasmodesmata in Plant CellsPlasmodesmata are channels that perforate plant cell wallsThrough plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell© 2011 Pearson Education, Inc.Figure 6.31Interiorof cellInteriorof cell0.5 mPlasmodesmataPlasma membranesCell wallsTight Junctions, Desmosomes, and Gap Junctions in Animal CellsAt tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluidDesmosomes (anchoring junctions) fasten cells together into strong sheetsGap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells© 2011 Pearson Education, Inc.Figure 6.32Tight junctions preventfluid from movingacross a layer of cellsTight junctionTight junctionTEM0.5 mTEM1 mTEM0.1 mExtracellularmatrixPlasma membranesof adjacent cellsSpacebetween cellsIons or smallmoleculesDesmosomeIntermediatefilamentsGapjunctionThe Cell: A Living Unit Greater Than the Sum of Its PartsCells rely on the integration of structures and organelles in order to functionFor example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane© 2011 Pearson Education, Inc.Figure 6.UN01Nucleus(ER)(Nuclearenvelope)