Sinh học - Chapter 6: A tour of the cell

Compare the structure and functions of microtubules, microfilaments, and intermediate filaments. Explain how the ultrastructure of cilia and flagella relate to their functions. Describe the structure of a plant cell wall. Describe the structure and roles of the extracellular matrix in animal cells. Describe four different intercellular junctions.

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Chapter 6A Tour of the CellOverview: The Fundamental Units of LifeAll organisms are made of cells (Cell Theory).The cell is the simplest collection of matter that can live.Cell structure is correlated to cellular function.All cells are related by their descent from earlier cells (heredity / reproduction).Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsTo study cells, biologists use microscopes and the tools of biochemistryMicroscopy: Scientists use microscopes to visualize cells too small to see with the naked eye.In a light microscope (LM), visible light passes through a specimen and then through glass lenses, which magnify the image.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe quality of an image depends onMagnification, 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.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe size range of cells10 m1 m0.1 m1 cm1 mm100 µm10 µm1 µm100 nm10 nm1 nm0.1 nmAtomsSmall moleculesLipidsProteinsRibosomesVirusesSmallest bacteriaMitochondrionNucleusMost bacteriaMost plant and animal cellsFrog eggChicken eggLength of some nerve and muscle cellsHuman heightUnaided eyeLight microscopeElectron microscopeLMs (light microscopes) 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.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsLightMicroscopyTECHNIQUERESULTS(a) Brightfield unstained specimen(b) Brightfield stained specimen50 µm(c) Phase-contrast(d) Differential-interference- contrast (Nomarski)(e )Fluorescence(f) Confocal50 µm50 µmTwo 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.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsElectronmicroscopy(a) Scanning electron microscopy (SEM)SurfaceTECHNIQUERESULTS(b) Transmission electron microscopy (TEM)Internal structuresCiliaLongitudinalsection ofciliumCross sectionof cilium1 µm1 µmCell FractionationCell fractionation takes cells apart and separates the major organelles from one another.Ultracentrifuges fractionate cells and separate their component parts by density.Cell fractionation enables scientists to determine the functions of organelles.Biochemistry and cytology help correlate cell function with structure.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsCellfractionationHomogenizationTECHNIQUEHomogenateTissuecells1,000 g(1,000 times theforce of gravity)10 minDifferential centrifugation : densitySupernatant pouredinto next tube20,000 g20 min80,000 g60 minPellet rich innuclei andcellular debrisPellet rich inmitochondria(and chloro-plasts if cellsare from a plant)Pellet rich in“microsomes”(pieces of plasmamembranes andcells’ internalmembranes)150,000 g3 hrPellet rich inribosomesCell Fractionation: Part 1HomogenizationHomogenateDifferential centrifugationTissuecellsTECHNIQUECell Fractionation: Part 21,000 g(1,000 times the force of gravity)10 minSupernatant poured into next tube20,000 g20 min80,000 g60 min150,000 g3 hrPellet rich in nuclei and cellular debrisPellet rich in mitochondria (and chloro-plasts if cellsare from a plant)Pellet rich in “microsomes” (pieces of plasmamembranes and cells’ internal membranes)Pellet rich in ribosomesTECHNIQUE (cont.)Eukaryotic cells have internal membranes that compartmentalize their functionsCell = the basic structural and functional unit of all life. (Cell Theory).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.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsComparing Prokaryotic vs. Eukaryotic CellsBasic features of all cells: Plasma membraneSemifluid substance called cytosol (cytoplasm)Chromosomes (carry genes) DNARibosomes (make proteins)Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsProkaryotic cells are characterized by havingNo nucleusDNA in an unbound region called the nucleoid.No membrane-bound organelles.Cytoplasm bound by the plasma membrane.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Prokaryotic CellFimbriaeNucleoidRibosomesPlasma membraneCell wallCapsuleFlagellaBacterialchromosome(a)A typical rod-shaped bacterium(b)A thin section through the bacterium Bacillus coagulans (TEM)0.5 µmEukaryotic cells are characterized by havingDNA in a nucleus that is bounded by a membranous nuclear envelope.Membrane-bound organellesCytoplasm in the region between the plasma membrane and nucleus.Eukaryotic cells are generally much larger than prokaryotic cells.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe plasma membrane is a selective barrier (semi-permeable) 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.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPlasma MembraneTEM of a plasma membrane(a)(b) Structure of the plasma membraneOutside of cellInside ofcell0.1 µmHydrophilicregionHydrophobicregionHydrophilicregionPhospholipidProteinsCarbohydrate side chainThe logistics of carrying out cellular metabolism sets 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 n3Small cells have a greater surface area relative to volume.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsGeometric relationshipsbetween surface area and volumeSurface area increases whiletotal volume remains constant51161507501251251661.2Total surface area[Sum of the surface areas(height  width) of all boxessides  number of boxes]Total volume[height  width  length number of boxes]Surface-to-volume(S-to-V) ratio[surface area ÷ volume]Eukaryotic cell: animal cellENDOPLASMIC RETICULUM (ER)Smooth ERRough ERFlagellumCentrosomeCYTOSKELETON:MicrofilamentsIntermediatefilamentsMicrotubulesMicrovilliPeroxisomeMitochondrionLysosomeGolgiapparatusRibosomesPlasma membraneNuclearenvelopeNucleolusChromatinNUCLEUSEukaryotic Cell: Plant CellNUCLEUS:Nuclear EnvelopeNucleolusChromatinRough endoplasmic reticulum ( Rough ER)Smooth endoplasmic reticulum (Smooth ER)RibosomesCentral vacuoleMicrofilamentsIntermediate filamentsMicrotubulesCYTO-SKELETONChloroplastPlasmodesmataWall of adjacent cellCell wallPlasma membranePeroxisomeMitochondrionGolgiapparatusThe Nucleus: Information Central : DNAThe 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.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings: The nucleus and its envelopeNucleolusNucleusRough ERNuclear lamina (TEM)Close-up of nuclear envelope1 µm1 µm0.25 µmRibosomePore complexNuclear poreOuter membraneInner membrane Nuclear envelope:ChromatinSurface ofnuclear envelopePore complexes (TEM)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.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsIn the nucleus, DNA and proteins form genetic material called chromatin. Chromatin condenses to form discrete chromosomes.The nucleolus is located within the nucleus and is the site of ribosomal RNA rRNA synthesis.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsRibosomes: Protein FactoriesRibosomes 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 - ER).Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings RibosomesCytosolEndoplasmic reticulum (ER)Free ribosomesBound ribosomesLarge subunitSmall subunitDiagram of a ribosomeTEM showing ER and ribosomes0.5 µmThe endomembrane system regulates protein traffic and performs metabolic functions in the cellComponents of the endomembrane system:Nuclear envelopeEndoplasmic reticulum: ERGolgi apparatusLysosomesVacuolesPlasma membraneThese components are either continuous or connected via transfer by vesicles.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe Endoplasmic Reticulum: Biosynthetic FactoryThe 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, with ribosomes studding its surface.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsEndoplasmicReticulum ERSmooth ERRough ERNuclear envelopeTransitional ERRough ERSmooth ERTransport vesicleRibosomesCisternaeER lumen200 nmFunctions of Smooth ERThe smooth ERSynthesizes lipidsMetabolizes carbohydratesDetoxifies poisonStores calcium Ca+Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFunctions of Rough ERThe rough ERHas bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates).Distributes transport vesicles, proteins surrounded by membranes.Is a membrane factory for the cell.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe Golgi apparatus consists of flattened membranous sacs called cisternae.Functions of the Golgi apparatus:Modifies products of the ERManufactures certain macromoleculesSorts and packages materials into transport vesicles.The Golgi Apparatus: Shipping and Receiving CenterCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsGolgi apparatuscis face(“receiving” side of Golgi apparatus)Cisternaetrans face(“shipping” side of Golgi apparatus)TEM of Golgi apparatus0.1 µmLysosomes: Digestive CompartmentsA lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules.Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids.Helps to breakdown and recycle cell material.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsSome 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.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsNucleus1 µmLysosomeDigestiveenzymesLysosomePlasmamembraneFood vacuole(a) Phagocytosis :engulfsDigestion (b) Autophagy : recycles PeroxisomeVesicleLysosomeMitochondrionPeroxisomefragmentMitochondrionfragmentVesicle containingtwo damaged organelles1 µmDigestionLysosomesFood vacuoles are formed by phagocytosis.Contractile vacuoles, found in many freshwater protists, pump excess water out of cells: osmoregulation.Central vacuoles, found in many mature plant cells, hold organic compounds and water.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsVacuoles: Diverse Maintenance CompartmentsThe plant cell vacuoleCentral vacuoleTonoplast = central vacuole membraneCytosolCentral vacuoleNucleusCell wallChloroplast5 µm The Endomembrane SystemSmooth ERNucleusRough ERPlasma membranecis Golgitrans GolgiMitochondria and Chloroplasts change energy from one form to anotherMitochondria are the sites of aerobic cellular respiration, a metabolic process that generates ATP.Chloroplasts, found in plants and algae, are the sites of photosynthesis.Peroxisomes are oxidative organelles.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsMitochondria and Chloroplasts:Are not part of the endomembrane systemHave a double membraneHave proteins made by free ribosomesContain their own DNA.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsMitochondria: Chemical Energy ConversionMitochondria are in nearly all eukaryotic cells.They have a smooth outer membrane and an inner membrane folded into cristae.The inner membrane creates two compartments: intermembrane space and mitochondrial matrix.Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix.Cristae present a large surface area for enzymes that synthesize ATP.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe mitochondrion = site of cellular respirationFree ribosomesin the mitochondrial matrixIntermembrane spaceOuter membraneInner membraneCristaeMatrix0.1 µmChloroplasts: Capture of Light EnergyThe chloroplast is a member of a family of organelles called plastids.Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis: water + carbon dioxide = sugar + oxygen. Chloroplasts are found in leaves and other green organs of plants and in algae.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsChloroplast structure includes:Thylakoids, membranous sacs, stacked to form a granum : light dependent reactions.Stroma, the internal fluid: Calvin Cycle = light independent reactions.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe chloroplast = site of photosynthesis ChloroplastRibosomesThylakoidStromaGranumInner and outer membranes1 µmPeroxisomes: OxidationPeroxisomes are specialized metabolic compartments bounded by a single membrane.Peroxisomes produce hydrogen peroxide and convert it to water.Oxygen is used to break down different types of molecules.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe cytoskeleton is a network of fibers that organizes structures and activities in the cellThe cytoskeleton is a network of fibers extending throughout the cytoplasm.It organizes the cell’s structures and activities, anchoring many organelles.It is composed of three types of molecular structures:MicrotubulesMicrofilamentsIntermediate filamentsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe cytoskeletonMicrotubuleMicrofilaments0.25 µmRoles of the Cytoskeleton: Support, Motility, and RegulationThe cytoskeleton helps to support the cell and maintain its shape.It interacts with motor proteins to produce motility.Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton.Recent evidence suggests that the cytoskeleton may help regulate biochemical activities.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsThe cytoskeletonVesicleATPReceptor for motor proteinMicrotubuleof cytoskeletonMotor protein (ATP powered)(a)MicrotubuleVesicles(b)0.25 µmComponents of the CytoskeletonThree main types of fibers make up the cytoskeleton:Microtubules 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.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings10 µm10 µm10 µmColumn of tubulin dimers Tubulin dimerActin subunit 25 nm7 nmKeratin proteins Fibrous subunit (keratins coiled together) 8–12 nm10 µmColumn of tubulin dimersTubulin dimer25 nmActin subunit10 µm7 nm5 µmKeratin proteinsFibrous subunit (keratinscoiled together)8–12 nmMicrotubulesMicrotubules are hollow rods about 25 nm in diameter and about 200 nm to 25 microns longFunctions of microtubules:Shaping the cellGuiding movement of organellesSeparating chromosomes during cell divisionCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Centrosomes and CentriolesIn many cells, microtubules grow out from a centrosome near the nucleusThe centrosome = “microtubule-organizing center” = MTOCIn animal cells, the centrosome has a pair of centrioles 9x3 Each centriole has nine triplets of microtubules arranged in a ring.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsCentrosomeMicrotubuleCentrioles0.25 µmLongitudinal section of one centrioleMicrotubulesCross sectionof the other centriole Cilia and FlagellaMicrotubules control the beating of cilia and flagella, locomotor appendages of some cells.Cilia and flagella differ in their beating patterns.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsComparisonof thebeating offlagella andcilia.5 µmDirection of swimming(a) Motion of flagellaDirection of organism’s movementPower strokeRecovery stroke(b) Motion of cilia15 µmCilia and flagella share a common ultrastructure:A core of microtubules sheathed by the plasma membrane.A basal body that anchors the cilium or flagellum.A motor protein called dynein, which drives the bending movements of a cilium or flagellum.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsUltrastructure of a eukaryotic flagellum or motile cilium0.1 µmTriplet(c) Cross section of basal body 9x3(a)Longitudinal section of cilium0.5 µmPlasma membraneBasal bodyMicrotubules(b)Cross section of cilium 9x2Plasma membraneOuter microtubule doubletDynein proteinsCentral microtubuleRadial spokeProtein cross-linking outer doublets0.1 µmThe motor protein, dynein, moves flagella and cilia by “walking” :Dynein arms alternately grab, move, and release the outer microtubules.Protein cross-links limit sliding.Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsHow dynein “walking” moves flagella and ciliaMicrotubuledoubletsDyneinproteinATPATP(a) Effect of unrestrained dynein movementCross-linking proteinsinside outer doubletsAnchoragein cell(b) Effect of cross-linking proteins132(c) Wavelike motionMicrofilaments (Actin Filaments)Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of protein actin subunits.The structural role of microfilaments is to bear tension, resisting pulling forces within the cell.They form a 3-D network called the cortex just inside the plasma membrane to help support the cell’s shape.Bundles of microfilaments make up the core of microvilli of intestinal cells.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsMicrofilaments that function in cellular motility contain the protein myosin in addition to actin.In muscle cells, thousands of actin filaments are arranged parallel to one another.Thicker filaments composed of myosin interdigitate with the thinner actin fibers.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsMicrofilaments and motilityMuscle cellActin filamentMyosin filamentMyosin arm(a) Myosin motors in muscle cell contractionCortex (outer cytoplasm):gel with actin networkInner cytoplasm: solwith actin subunitsExtendingpseudopodium(b) Amoeboid movementNonmoving corticalcytoplasm (gel)ChloroplastStreamingcytoplasm(sol)VacuoleCell wallParallel actinfilaments(c) Cytoplasmic streaming in plant cellsSarcomere – muscle cell unit of contractionMuscle cellActin filamentMyosin filamentMyosin arm(a) Myosin motors in muscle cell contractionCortex (outer cytoplasm): gel with actin networkInner cytoplasm: sol with actin subunitsExtending pseudopodium(b) Amoeboid movementNonmoving cortical cytoplasm (gel)ChloroplastCell wallStreaming cytoplasm (sol)Parallel actin filaments(c) Cytoplasmic streaming in plant cellsVacuoleLocalized contraction brought about by actin and myosin also drives amoeboid movement.Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsCytoplasmic streaming is a circular flow of cytoplasm within cells.This streaming speeds distribution of materials within the cell.In plant cells, actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsIntermediate FilamentsIntermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubules.They support cell shape and fix organelles in place.Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsExtracellular components and connections between cells help coordinate cellular activitiesMost cells synthesize and secrete materials that are external to the plasma membraneThese extracellular structures include:Cell walls of plantsThe extracellular matrix (ECM) of animal cellsIntercellular junctionsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsCell Walls of PlantsThe cell wall is an extracellular structure that distinguishes plant cells from animal cells.Prokaryotes, fungi, and some protists also have cell walls.The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water.Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPlant cell walls may have multiple layers:Primary cell wall: relatively thin and flexibleMiddle lamella: thin layer between primary walls of adjacent cellsSecondary cell wall (in some cells): added between the plasma membrane and the primary cell wall.Plasmodesmata are channels between adjacent plant cells.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPlant cell wallsSecondary cell wallPrimary cell wall outermost of the cell wallsMiddle lamellaCentral vacuoleCytosolPlasma membranePlant cell wallsPlasmodesmata1 µmThe 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 fibronectin.ECM proteins bind to receptor proteins in the plasma membrane called integrins.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsExtracellular matrix (ECM) of an animal cellEXTRACELLULAR FLUIDCollagenFibronectinPlasmamembraneMicro-filamentsCYTOPLASMIntegrinsProteoglycancomplexPolysaccharidemoleculeCarbo-hydratesCoreproteinProteoglycanmoleculeProteoglycan complexECM of Animal cellCollagenFibronectinPlasma membraneProteoglycan complexIntegrinsCYTOPLASMMicro-filamentsEXTRACELLULAR FLUIDFunctions of the ECM:SupportAdhesionMovementRegulationIdentification “ID” cell-to-cell recognitionCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsIntercellular 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 junctions*Plasmodesmata = channels / plant cells*Gap junctions = channels / animal cellsTight junctions – waterproofDesmosomes - anchorsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPlasmodesmata in Plant CellsPlasmodesmata are channels that perforate plant cell walls.Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPlasmodesmata between plant cellsInterior of cellInterior of cell0.5 µmPlasmodesmataPlasma membranesCell wallsTight Junctions, Desmosomes, and Gap Junctions in Animal CellsAt tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid waterproof.desmosomes (anchoring junctions) fasten cells together into strong sheets.gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsIntercellular junctions in animal tissuesTight junction0.5 µm1 µmDesmosomeGap junctionExtracellularmatrix0.1 µmPlasma membranesof adjacent cellsSpacebetweencells GapjunctionsDesmosomeIntermediatefilamentsTight junctionTight junctions preventfluid from movingacross a layer of cellsThe Cell: A Living Unit Greater Than the Sum of Its PartsCells rely on the integration of structures and organelles in order to function.For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings5 µmThe emergence of cellular functions –> Macrophages’s ability to engulf and destroy bacteriaCell Structures & FunctionsCell Component Structure Function Houses chromosomes, made ofchromatin (DNA, the geneticmaterial, and proteins); containsnucleoli, where ribosomalsubunits are made. Poresregulate entry and exit ofmaterials. Nucleus (ER) Concept 6.3 The eukaryotic cell’s geneticinstructions are housed inthe nucleus and carried outby the ribosomes Ribosome Concept 6.4 Endoplasmic reticulum The endomembrane systemregulates protein traffic andperforms metabolic functionsin the cell (Nuclearenvelope) Concept 6.5 Mitochondria and chloro-plasts change energy fromone form to another Golgi apparatus Lysosome Vacuole Mitochondrion Chloroplast PeroxisomeTwo subunits made of ribo-somal RNA and proteins; can befree in cytosol or bound to ERExtensive network ofmembrane-bound tubules andsacs; membrane separateslumen from cytosol;continuous withthe nuclear envelope.Membranous sac of hydrolyticenzymes (in animal cells) Large membrane-boundedvesicle in plantsBounded by doublemembrane;inner membrane hasinfoldings (cristae)Typically two membranesaround fluid stroma, whichcontains membranous thylakoidsstacked into grana (in plants)Specialized metaboliccompartment bounded by asingle membraneProtein synthesis Smooth ER: synthesis oflipids, metabolism of carbohy-drates, Ca2+ storage, detoxifica-tion of drugs and poisons Rough ER: Aids in synthesis ofsecretory and other proteins frombound ribosomes; addscarbohydrates to glycoproteins;produces new membrane Modification of proteins, carbo-hydrates on proteins, and phos-pholipids; synthesis of manypolysaccharides; sorting of Golgiproducts, which are then released in vesicles. Breakdown of ingested substances,cell macromolecules, and damagedorganelles for recycling Digestion, storage, wastedisposal, water balance, cellgrowth, and protectionCellular respiration Photosynthesis Contains enzymes that transferhydrogen to water, producinghydrogen peroxide (H2O2) as aby-product, which is convertedto water by other enzymesin the peroxisome Stacks of flattenedmembranoussacs; has polarity(cis and transfaces) Surrounded by nuclearenvelope (double membrane)perforated by nuclear pores.The nuclear envelope iscontinuous with theendoplasmic reticulum (ER).Cell Component Structure Function Concept 6.3 The eukaryotic cell’s Genetic Instructionsare housed inthe nucleus and carried outby the ribosomes Nucleus Surrounded by nuclearenvelope (double membrane)perforated by nuclear pores.The nuclear envelope iscontinuous with theendoplasmic reticulum (ER). (ER) Houses chromosomes, made ofchromatin (DNA, the geneticmaterial, and proteins); containsnucleoli, where ribosomalsubunits are made. Poresregulate entry and exit osmaterials. Ribosome Two subunits made of ribo-somal RNA and proteins; can befree in cytosol or bound to ER Protein synthesis Cell Component Structure Function Concept 6.4 The endomembrane systemregulates protein traffic andperforms metabolic functionsin the cell Endoplasmic reticulum (Nuclearenvelope) Golgi apparatus Lysosome Vacuole Large membrane-boundedvesicle in plants Membranous sac of hydrolyticenzymes (in animal cells) Stacks of flattenedmembranoussacs; has polarity(cis and transfaces) Extensive network ofmembrane-bound tubules andsacs; membrane separateslumen from cytosol;continuous withthe nuclear envelope. Smooth ER: synthesis oflipids, metabolism of carbohy-drates, Ca2+ storage, detoxifica-tion of drugs and poisons Rough ER: Aids in sythesis ofsecretory and other proteinsfrom bound ribosomes; addscarbohydrates to glycoproteins;produces new membraneModification of proteins, carbo-hydrates on proteins, and phos-pholipids; synthesis of manypolysaccharides; sorting ofGolgi products, which are thenreleased in vesicles. Breakdown of ingested sub-stances cell macromolecules, and damaged organelles for recycling Digestion, storage, wastedisposal, water balance, cellgrowth, and protection Cell Component Concept 6.5Mitochondria and chloroplasts change energy fromone form to anotherMitochondrion Chloroplast PeroxisomeStructure Function Bounded by doublemembrane;inner membrane hasinfoldings (cristae) Typically two membranesaround fluid stroma, whichcontains membranous thylakoidsstacked into grana (in plants) Specialized metaboliccompartment bounded by asingle membrane Cellular respiration Photosynthesis Contains enzymes that transferhydrogen to water, producinghydrogen peroxide (H2O2) as aby-product, which is convertedto water by other enzymesin the peroxisome You should now be able to:Distinguish between the following pairs of terms: magnification and resolution; prokaryotic and eukaryotic cell; free and bound ribosomes; smooth and rough ER.Describe the structure and function of the components of the endomembrane system.Briefly explain the role of mitochondria, chloroplasts, and peroxisomes.Describe the functions of the cytoskeleton.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsCompare the structure and functions of microtubules, microfilaments, and intermediate filaments.Explain how the ultrastructure of cilia and flagella relate to their functions.Describe the structure of a plant cell wall.Describe the structure and roles of the extracellular matrix in animal cells.Describe four different intercellular junctions.Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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