Chapter 6 Cell Structures and Their Functions

Chapter 3Cell Structure and FunctionEukaryotic Cell Structure

Chemical Components of CellsMost cells are composed of 4 elementsCarbonHydrogenOxygenNitrogenCells are about 60% waterAnatomy of a Generalized CellCells have 4 main regions (parts)NucleusCytoplasmPlasma Membrane

Nucleus

Control centerCell reproduction DNA --Visible ChromosomesNuclear envelopeDouble membranePoresNucleolirRNA and tRNA assembly

Cell Membrane-fluid mosaicControls movement into and out of the cellComposed of lipid and protein bilayerCholesterolGlycolipidsGlycoproteins

Components of Cell Membrane(Fluid Mosaic Model) Phospholipids (bilayer)Phospholipids Hydrophillic (water loving) Head: Phosphate and glycerolHydrophobic Tails (water hating): impermeable to most water soluble molelculesCholesterol membrane fluidityProteins: Receptors, enzymes, transport channels or carriersReceptors: Glycoproteins and GlycolipidsBlood type, organ transplant rejection

ORGANELLESSpecialized cellular compartmentsMany membrane bound

Cytoplasm (Cytosol)Semi-fluid material suspends other elementsContains enzymes

MitochondrionDouble membraneInternal foldsCellular Respiration!!! Energy for cellContains its own DNA and RNA

RibosomesSite of Protein synthesisFound free in cytoplasmAs a part of the Rough ER

Endoplasmic Reticulum

Fluid Filled Tubules Rough ERContains RibosomesMoves proteins within cellSmooth ERNo RibosomesProtein modificationLipid metabolism

Rough ER

Golgi Apparatus

Flattened sacs Modifies, Sorts, and packages proteins arriving from ER for delivery

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Golgi AnimationMaterials are transported from Rough ER to Golgi to the cell membrane by VESICLES

153 types of packages

Lysosomes

Intracellular digestion (enzymes)Membranous bags from golgi apparatus Fuse with vesiclesIngested food Damaged organelles

Tay-Sachs disease-missing or inactive lysosomal enzymes

Cytoskeleton

Protein network made ofMicrofilamentsintermediate filamentsMicrotubulesCell ShapeInternal OrganizationOrganelle Movement!

Figure 3.7 Cytoskeletal elements support the cell and help to generate movement.Actin subunit7 nmFibrous subunitsTubulin subunits10 nm25 nmMicrofilaments form the bluebatlike network.(a) Microfilaments(b) Intermediate filaments(c) MicrotubulesIntermediate filaments formthe purple networksurrounding the pink nucleus.Microtubules appear as goldnetworks surrounding thecells pink nuclei.19Centrioles

Rod shaped made of Microtubules Before mitosis-pairs duplicate + separateProduces Mitotic Spindles

Cilia and FlagellaCell movement Sperm cells-flagellaMovement of materials along surfaceRespiratory tract-ciliaMicrovilli fingerlike extensions Increase surface area for absorption22Cilia Moving Away Dust Particles from the LungsRespiratory System

22Membrane TransportTwo basic methodsPassive Transport (no energy required)Active Transport (energy required ATP)Passive TransportDiffusion Simple: lipid soluble or smallOsmosis: water moves thru aquaporinsFacilitated: use carriersFiltration

Passive Transport: FiltrationWater and solutes are forced through a membrane because of a pressure gradientThrough capillary wallsMovement of water or small solutesKidneys-blood filtrationActive TransportSolute pumpingRequires protein carriersATP used Examples: sodium/potassium pump

Active TransportEndocytosis: into the cellPhagocytosis: engulfing large particlesPinocytosis: cell drinking

Exocytosis: movement out of the cell

Figure 3.12b Exocytosis.(b) Electron micrograph of asecretory vesicle inexocytosis (190,000)28

Figure 3.13b Events and types of endocytosis.PseudopodBacteriumor otherparticleExtracellularfluidCytoplasm(b)29

Figure 3.13a Events and types of endocytosis.PlasmamembraneLysosomePitIngestedsubstanceDetached vesicleVesicleExtracellularfluidCytosolRelease ofcontents tocytosolVesicle fusingwith lysosomefor digestionTransport to plasmamembrane and exocytosisof vesicle contentsMembranes and receptors(if present) recycled to plasmamembrane1(a)23Slide 430Cell Life CycleINTERPHASECell growthCarries on regular cell activitiesCELL DIVISIONCell replicates itself to produce more cells for growth and repairInterphaseG1: growth protein synthesis, organelles doubleS: synthesis phaseDNA replication/duplicated chromosomesG2: Protein synthesis, chromatin condenses, chromosomes visible, final preparation to divide

Cell DivisionMitosis division of the nucleusResult: 2 daughter nucleiCytokinesis division of the cytoplasmResult: 2 daughter cells

SpindlemicrotubulesChromosome,consisting of twosister chromatidsFragments ofnuclear envelopeDaughterchromosomesFigure 3.15 Stages of mitosis.CentriolesChromatinCentriolesFormingmitoticspindleCentromereCentromerePlasmamembraneNuclearenvelopeNucleolusSpindlepoleMetaphaseplateNucleolusformingCleavagefurrowSpindleSisterchromatidsNuclearenvelopeformingInterphaseEarly prophaseLate prophaseMetaphaseAnaphaseTelophase and cytokinesisSlide 135CytokinesisDivision of cytoplasmCell pinched into 2 daughter cells

Protein Synthesis (into) (into) DNA mRNA Protein transcription translation

As the ribosomemoves along the mRNA,a new amino acid isadded to the growingprotein chain.Released tRNAreenters thecytoplasmic pool,ready to be rechargedwith a new aminoacid.mRNA specifying onepolypeptide is made onDNA template.mRNA leavesnucleus and attachesto ribosome, andtranslation begins.Incoming tRNArecognizes acomplementarymRNA codon callingfor its amino acid bybinding via its anticodonto the codon.mRNAFigure 3.16 Protein synthesis.Nuclear membrane21345Nuclear poreNucleus(site of transcription)DNAAminoacidsCytoplasm(site of translation)SynthetaseenzymeCorrect aminoacid attached toeach species oftRNA by an enzymeGrowingpolypeptidechainPeptide bondtRNA headbearing anticodonLarge ribosomal subunitCodonPortion ofmRNA alreadytranslatedSmall ribosomal subunitDirection ofribosome advance;ribosome moves themRNA strand alongsequentially as each codon is read.MetGlySerPheAlaSlide 138