A Tour of the Cell

Centrosomes and CentriolesFlagellumENDOPLASMIC RETICULUM (ERRough ERSmooth ERNuclear envelopeNucleolusNUCLEUSChromatin•In many cells, microtubules grow out from acentrosome near the nucleusCentrosomePlasma membraneThe centrosomeCYTOSKELETONMicrofilamentsIntermediate filamentsMicrotubulesRibosomes:In animal cells, the centrosome has a pair of centrioles,MicrovilliGolgi apparatusPeroxisomeMitochondrionLysosomeIn animal cells but not plant cells:LysosomesCentriolesFlagella (in some plant sperm)Cilia and FlagellaCentrosomeMicrotubules control the beating of cilia andflagella, locomotor appendages of some cellsCilia and flagella differ in their beating patternsCentriolesMicrotubuleMotion of flagellaDirection of organism’s movementLongitudinal sectionof one centrioleMicrotubulesCross sectionof the other centrioleDirection ofactive strokeDirection ofrecovery stroke•Cilia and flagella share a common ultrastructure:A core of microtubulesA basal bodyMotion of ciliaA motor protein called dynein, which drivesthe bending movements of a cilium orflagellumMicrotubulesPlasmamembraneBasal bodyCross section of basal body

Components of the CytoskeletonMicrofilaments•Microfilaments are solid rods about 7 nmin diameter, built as a twisted double chainof actin subunitsMicrofilaments (Actin Filaments)•The structural role of microfilaments is toMicrovillus•Bundles of microfilaments make up the core ofmicrovilli of intestinal cellsPlasma membraneMicrofilaments (actinfilaments)•In muscle cells, thousands of actin filaments arearranged parallel to one anotherIntermediate filaments•Thicker filaments composed of myosin interdigitate withthe thinner actin fibersMuscle cellActin filamentMyosin filamentMyosin arm•Pseudopodia (cellular extensions) extend andcontract through the reversible assembly andcontraction of actin subunits into microfilamentsCytoplasmic streamingExtendingpseudopodiumMyosin motors in muscle cell contractionInner cytoplasm: solwith actin subunitsCortex (outer cytoplasm):gel with actin networkThis streaming speeds distribution of materials within the cellAmoeboid movementNonmovingcytoplasm (gel)ChloroplastStreamingcytoplasm(sol)VacuoleParallel actinfilamentsCell wallCytoplasmic streaming in plant cells

Components of the CytoskeletonIntermediate Filaments•Intermediate filaments range in diameter from 8–12nanometers, larger than microfilaments but smaller thanmicrotubules•They support cell shape and fix organelles in placeExtracellular components and connections between cellshelp coordinate cellular activities•Most cells synthesize and secrete materials that are external to the plasma membrane•These extracellular structures include:Cell Walls of PlantsThe cell wall is an extracellular structure thatdistinguishes plant cells from animal cells•Plant cell walls may have multiple layers:–Primary cell wall:Centralvacuoleof cellPlasmamembraneSecondarycell wallPrimarycell wall–Middle lamella:Centralvacuoleof cellMiddlelamella–Secondary cell wall (in some cells:Central vacuole1 µmCytosolPlasma membranePlant cell wallsPlants: PlasmodesmataPlasmodesmataCell wallsInteriorof cell•Through plasmodesmata, water and small solutes (andsometimes proteins and RNA) can pass from cell to cellInteriorof cellPlasmodesmataPlasma membranes

The Extracellular Matrix (ECM) of Animal Cells•Functions of the ECM:Intercellular Junctions•Neighboring cells in tissues, organs, or organ systemsoften adhere, interact, and communicate through directphysical contact•Intercellular junctions facilitate this contactAnimals: Tight Junctions, Desmosomes, and Gap JunctionsTight junctions preventfluid from movingacross a layer of cellsTight junction•DesmosomesTight junction•Gap junctionstight junctionsSpacebetweencellsDesmosomeGapjunctionsGap junctionExtracellularmatrix

Study outline-Chapter 6-A Tour of the Cell-Understand the structure and function of the cytoskeleton-Know three types of fibers of the cytoskeleton: microtubules, microfilaments, intermediate filaments-Understand the structure of centrosomes and centrioles-Know the structure and function of cilia and flagella (Fig. 6.24)-Understand movement of cytoplasmic streaming and amoeboid movement-Know terms-cytoskeleton, microtubule, microfilament, intermediate fibers, centrosomes, centriole, cilia, flagella,dynein, basal body, myosin, actin, amoeboid movement, pseudopodia, cytoplasmic streaming-Understand extracellular components and connections-Know and recognize plant cell walls, extracellular matrix of animal cells and intracellular junctions-Understand structure of plant cell walls (primary, secondary, and middle lamellae) and plamodesmata.-Understand and recognize components and functions of extracellular matrix of animal cells-Know the structure and function of intercellular junctions-tight junctions, desmosomes, and gap junctions-Understand differences between plant and animal cells