Chapter 02 Cytology Notes

Microscopy and Imaging

  • Microscopy types and purpose
    • Light microscope (LM)
    • Uses visible light to produce the image; most often used in teaching and clinical labs.
    • Least magnification among common microscope types but useful for live cells and general structure.
    • Transmission electron microscope (TEM)
    • Uses electrons to produce highly detailed internal structures; very high resolution for viewing organelles and ultrastructure.
    • Scanning electron microscope (SEM)
    • Produces 3D-like surface images; excellent for external morphology of cells and textures.
  • Key concept: Magnification vs. resolution
    • Magnification increases apparent size, while resolution is the ability to reveal fine detail and separate adjacent features.
    • LM vs TEM vs SEM differences illustrated in Figures (e.g., Fig. 2.1a,b; Fig. 2.2a,b,c).
  • RBC (red blood cell) imaging across modalities
    • Images of RBCs produced by LM, SEM, and TEM show progressive detail from surface outline to internal features.
    • Example dimensions mentioned for reference:
    • LM and SEM examples show cells around
      ext10.0μextmext{10.0 }\mu ext{m} scale (SEM image) and
    • TEM can reveal structures as small as a few hundred nanometers (noted by scale bars in figures).
  • Units and scale notes
    • Micrometer:
      ext{1 micrometer} = 10^{-6} ext{ m} = oldsymbol{1} ext{ } oldsymbol{ imes} oldsymbol{10^{-6}} ext{ m}
    • Naked eye resolution: about
      ext{100 }oldsymbol{BC} ext{m} (100 μm).

Cell Shapes and Sizes

  • Common cell shapes (Fig. 2.3):
    • Squamous: flat and scale-like
    • Cuboidal: as tall as they are wide
    • Columnar: taller than wide
    • Polygonal: irregular, multi-angled
    • Stellate: star-shaped with multiple processes
    • Spheroidal: ball-shaped
    • Discoidal: disc-like
    • Fusiform: spindle-shaped (thicker in middle, tapered ends)
    • Fibrous: elongated and thread-like
  • Cells vary in size and shape depending on function and tissue context.

Cellular Terminology and Basic Units

  • Polar surfaces of a cell

    • Basal surface: oriented toward the basal membrane.
    • Apical surface: faces toward lumen or external environment.
    • Lateral surface: faces adjacent cells.

  • Measurement unit

    • Micrometer (
      oldsymbol{BC}D

    )

    • One-millionth of a meter:
      1 ext{ }oldsymbol{BC} ext{m} = 10^{-6} ext{ m}</li></ul></li><li><p>Basiccellconcepts</p><ul><li>Cellcomponentsinclude:</li><li>Plasmamembrane</li><li>Cytoplasm</li><li>Cytoskeleton</li><li>Organelles</li><li>Inclusions</li><li>Cytosol</li><li>Nucleusisanorganellecontainingnucleoplasm.</li></ul></li></ul><h3id="generalizedcellandorganellesfig2528">GeneralizedCellandOrganelles(Fig.2.5,2.8)</h3><ul><li>Generalizedcelllayout(apical,lateral,basalsurfaces)withmajororganellesandstructures:<ul><li>Microvilli:plasmamembraneextensionsincreasingsurfacearea;oftencalledbrushborder.</li><li>DesmosomesandHemidesmosomes:cell–cellandcell–basementmembraneadhesionsrespectively.</li><li>Secretoryvesicle,Golgivesicles,Golgicomplex:involvedinprocessingandshippingproteins.</li><li>Roughendoplasmicreticulum(RER):studdedwithribosomes;synthesizesphospholipidsandproteinsforplasmamembrane,secretion,andlysosomes.</li><li>Smoothendoplasmicreticulum(SER):detoxificationincertaincellsandsteroidsynthesisinothers.</li><li>Nucleus,Nucleolus,Nuclearenvelope;variouscomponentsshownincross−section.</li><li>Mitochondrion:siteofATPproduction.</li><li>Cytoskeletalcomponents:microfilaments,intermediatefilaments,microtubules;providestructureandtransportroutes.</li><li>Lysosome,peroxisome:organellesinvolvedindigestionandreactiveoxygenspeciesmanagement.</li><li>Centrioles,Centrosome:organizationcenterformicrotubulesduringcelldivision.</li></ul></li><li>Functionalcoordination<ul><li>Theplasmamembrane,cytoskeletalframework,andorganellescoordinatetomaintaincellstructure,transport,signaling,andmetabolism.</li></ul></li></ul><h3id="plasmamembranecompositionandproteins">PlasmaMembraneCompositionandProteins</h3><ul><li>Membranecomposition(Fig.2.9,2−11)<ul><li>Phospholipids: 75<li>Cholesterol: 20<li>Glycolipids: 5<li>Membraneproteinstypes<ul><li>Integral(transmembrane)proteins:spanthemembrane.</li><li>Peripheralproteins:associatedwithmembranefacesbutdonotspanthebilayer.</li><li>Glycoproteins:membraneproteinswithcarbohydratechains;partofglycocalyx.</li></ul></li><li>Membranearchitecture<ul><li>Phospholipidbilayerformsthestructuralfoundation.</li><li>Glycolipidsandglycoproteinsextendcarbohydratechainstotheextracellularsurface,formingglycocalyx.</li><li>Cytoskeleton−associatedproteinshelpanchormembraneandcontributetocellshape.</li></ul></li><li>Functionalrolesofmembraneproteins(Fig.2.9)<ul><li>Receptorproteins:receivesignalsfromtheenvironmentorothercells.</li><li>Enzymes:catalyzereactionsatthemembranesurface.</li><li>Channelproteins:formporesthatallowspecificionsormoleculestopass.</li><li>Transportproteins:movesubstancesacrossthemembrane.</li><li>Cell−identitymarkers:identifythecellasselfornon−self.</li><li>Cell−adhesionmolecules(CAMs):enablecellstoattachtoeachotherortotheextracellularmatrix.</li></ul></li><li>Membranepolarityandtransportinterfaces<ul><li>Extracellularfaceandintracellularfaceofthemembraneshowdistinctproteinandlipidarrangements(Fig.2.6b).</li></ul></li></ul><h3id="membranetransportmechanisms">MembraneTransportMechanisms</h3><ul><li>Filtration(Fig.2.10a)<ul><li>Capillarybloodpressureforceswaterandsmallsolutesthroughcleftsbetweencells.</li><li>Bigsolutesandbloodcellsareheldbackbytheclefts(selectivebarrier).</li></ul></li><li>Simplediffusion(Fig.2.10b)<ul><li>Lipid−solublesolutesdiffusedirectlythroughthephospholipidbilayerdowntheirconcentrationgradient.</li><li>Water−solublesolutesdiffusethroughchannelproteins(pores)downtheirconcentrationgradient.</li><li>Netmovementfromhightolowconcentration.</li></ul></li><li>Osmosis(specialcaseofdiffusion)<ul><li>Movementofwateracrossaselectivelypermeablemembranefromthemorewatery(higherwaterpotential)tothelesswateryside.</li></ul></li><li>Facilitateddiffusion(Fig.2.10c)<ul><li>Solutebindstoareceptorsiteonahigh−affinitytransportprotein.</li><li>Transportproteinchangesshapetoshuttlesoluteacrossthemembranedownitsconcentrationgradient.</li><li>DoesnotrequireATP;drivenbygradient.</li></ul></li><li>Activetransport(Fig.2.10d)<ul><li>Solutebindstoreceptorsiteontransportprotein;ATPhydrolysisprovidesenergy.</li><li>Phosphate(P)bindstotheprotein,inducingaconformationalchangetomovesoluteagainstitsgradient.</li><li>Requirescellularenergy;cancreateormaintainconcentrationgradients.</li><li>TypicalschematicincludesATP→ADPconversionandPtransfertotransporterprotein.</li></ul></li><li>Vesicular(bulk)transport(Fig.2.11)<ul><li>Pinocytosis(celldrinking):uptakeofextracellularfluidanddissolvedsolutesviapinch−offvesicles.</li><li>Receptor−mediatedendocytosis:selectiveuptakeofspecificligandsboundtomembranereceptors.</li><li>Exocytosis:secretoryvesiclesfusewiththeplasmamembranetoreleasecontentsoutsidethecell.</li><li>Allinvolvevesicleformation,trafficking,andfusiontodelivercargo.</li></ul></li></ul><h3id="surfaceextensionsandexternalfeatures">SurfaceExtensionsandExternalFeatures</h3><ul><li>Microvilli<ul><li>Plasmamembraneextensionsthatincreasesurfacearea,enhancingabsorptionandsignaling.</li></ul></li><li>Cilia<ul><li>Primarycilium:non−motile,sensoryantennaforsignalingpathways.</li><li>Motilecilia:containanaxonemeofmicrotubules;movesubstancesacrosscellsurfaces.</li><li>Axonemestructure:centralmicrotubulecorewithdyneinarms(motorproteins)drivingbending.</li></ul></li><li>Flagella<ul><li>Longaxoneme;primarilyusedtopropelspermcells.</li></ul></li><li>Visualreferences<ul><li>Figures2.12a,2.13showmicrovilli,cilia,andaxonemestructure.</li></ul></li></ul><h3id="glycocalyxandcellularjunctions">GlycocalyxandCellularJunctions</h3><ul><li>Glycocalyx<ul><li>Carbohydrate−rich“fuzzy”coatingontheextracellularsideofthemembrane.</li><li>Functions:protection,cellidentity,andbindingtotissues.</li></ul></li><li>Cellularjunctions(Fig.2.15)<ul><li>Tightjunctions:sealneighboringcellstopreventparacellularleakage.</li><li>Desmosomes:resistmechanicalstressbylinkingcytoskeletonsofadjacentcells.</li><li>Gapjunctions:allowdirectchemicalcommunicationbetweenneighboringcells.</li></ul></li></ul><h3id="thecellinteriorcytosolcytoskeletonandinclusions">TheCellInterior:Cytosol,Cytoskeleton,andInclusions</h3><ul><li>Cytosol<ul><li>Fluidportionofthecytoplasm,containingdissolvedsolutesandions.</li></ul></li><li>Cytoskeleton<ul><li>Structuralframeworkofthecell;determinesshape;organizescontents;movessubstancesandsometimesthecellitself.</li><li>Threemaincomponents:</li><li>Microfilamentsandterminalweb(thinfilaments):supportcellcortexandhelpwithmovement.</li><li>Intermediatefilaments:providetensilestrengthandstructuralintegrity.</li><li>Microtubules:provideroutesforintracellulartransportandformthemitoticspindle.</li></ul></li><li>Organelles<ul><li>“Littleorgans”;metabolicallyactive;compartmentalizecellularcontentsforspecializedfunctions.</li></ul></li><li>Inclusions<ul><li>Notessentialforcellsurvival;storescellularproductsorforeignmatter.</li><li>Examples:pigments,fatdroplets,granulesofglycogen;dustparticles,viruses,andintracellularbacteria(nonmetabolicinclusions).</li></ul></li></ul><h3id="thecytoskeletonindetailfig216">TheCytoskeletoninDetail(Fig.2.16)</h3><ul><li>Rolesofcytoskeletalelements<ul><li>Proteinfilamentsandtubulessupportcellstructure,determinecellshape,organizecellularcontents,movesubstances,andcandrivecellmovement.</li></ul></li><li>Interactionmap<ul><li>Microfilaments,microtubules,intermediatefilamentsinteractwithorganelleslikelysosomes,mitochondria,nucleus,centrosome,andmotorproteins(e.g.,kinesin)tocoordinatetransportandorganization.</li></ul></li><li>Visualcuesfromfigures:<ul><li>Secretoryvesicleintransport,desmosomes,microvilli,organelledistributionaroundthecytoskeleton,basalmembranecontext.</li></ul></li></ul><h3id="organellesthefunctionalunitswithinthecellfig218219e">Organelles:TheFunctionalUnitsWithintheCell(Fig.2.18–2.19e)</h3><ul><li>Nucleus<ul><li>Largestorganelle;containsthecell’schromosomes;geneticcontrolcenter.</li><li>Functionsincludeproductionofribosomes.</li><li>Keycomponents:nuclearenvelope,nuclearpores,nucleoplasm,chromosomes,nucleoli.</li></ul></li><li>Endoplasmicreticulum(ER)<ul><li>“Littlenetworkwithinthecytoplasm”withcisterns.</li><li>RoughER(RER):studdedwithribosomes;synthesizesphospholipidsandproteinsfortheplasmamembrane;proteinsforsecretionandlysosomes.</li><li>SmoothER(SER):detoxificationincells;synthesizessteroidsinsteroid−producingcells.</li></ul></li><li>Ribosomes<ul><li>Locations:cytosol,roughER,nuclearenvelope,nucleoli,mitochondria.</li><li>Function:translateRNAintoproteins;readmRNAandassembleaminoacidsintopolypeptidechains.</li></ul></li><li>Golgicomplex<ul><li>Consistsofcisterns;receivestransportvesiclesfromtheRER;formsGolgivesiclescontainingpackagedproteins.</li><li>Functionsincludelysosomeformation,directingproteinstotheplasmamembraneorsecretionviasecretoryvesicles.</li></ul></li><li>Proteasomes<ul><li>Cylindricalcomplexesthatdegradeandrecycledamagedorunneededproteins;degrade 80<li>Lysosomes<ul><li>Containenzymesinasingle−unitmembrane;cleanupcellviaautophagy(degradingorganelles)andapoptosis(programmedcelldeath).</li></ul></li><li>Peroxisomes<ul><li>Similartolysosomes;oxidizefattyacidsandotherorganicmolecules;producehydrogenperoxideanddegradeitwithcatalase;abundantinliverandkidneys.</li></ul></li><li>Mitochondria<ul><li>Powerhousesofthecell;specializedforaerobicrespirationandATPproduction.</li><li>Structure:outerandinnermembranes;cristae;mitochondrialmatrix;containmitochondrialDNA(mtDNA).</li></ul></li><li>Centrioles<ul><li>Composedofmicrotubulesina9−tripletarrangement.</li><li>Centrosome:cytoplasmregionthatcontainstheperpendicularpairofcentrioles;importantfororganizingspindleduringmitosis.</li><li>Basalbody:foundationforciliaandflagella.</li></ul></li><li>Inclusions(nonessentialstructures)<ul><li>Pigments,lipidorglycogengranules,andstoredproducts;foreignmaterialslikedustorbacteriacanalsoaccumulateasinclusions.</li></ul></li></ul><h3id="thecellcyclegrowthreplicationanddivisionfigs239243">TheCellCycle:Growth,Replication,andDivision(Figs.2.39–2.43)</h3><ul><li>Majorphases<ul><li>Interphase:growth,metabolicactivity,andDNAreplication.</li><li>G1(Firstgapphase):growthandnormalmetabolicroles.</li><li>S(Synthesisphase):DNAreplication.</li><li>G2(Secondgapphase):growthandpreparationformitosis;DNAproofreading.</li><li>Mitoticphase(M):divisionofnuclearmaterialandcytoplasm.</li><li>Prophase:chromatincondenses;nuclearenvelopebreaksdown;nucleolusdisappears;spindlefibersformandattachtokinetochores.</li><li>Metaphase:chromosomesalignatthecellcenter;astersattachtoplasmamembrane.</li><li>Anaphase:centromeressplit;sisterchromatidspulledtooppositepoles.</li><li>Telophase:chromatidsarriveatpoles;chromosomesdecondense;newnuclearenvelopeforms;nucleolireform;mitoticspindlevanishes.</li><li>Cytokinesis:divisionofcytoplasm;cleavagefurrowforms;cellsplitsintotwoidenticaldaughtercells.</li></ul></li><li>Visualreference:Fig.2.23illustratesstagesofmitosiswithlabeledstructures(centrioles,chromatids,kinetochores,mitoticspindle).</li></ul><h3id="stemcellsanddevelopmentalpotentials">StemCellsandDevelopmentalPotentials</h3><ul><li>Stemcellsdefined<ul><li>Immaturecellscapableofdevelopingintooneormoremature,specializedcelltypes;possessdevelopmentalplasticity.</li></ul></li><li>Adultstem(AS)cells<ul><li>Presentinmostbodyorgans;responsiblefornormalturnoverandmaintenanceoftissue.</li><li>Multipotentexample:bonemarrowcells(candifferentiateintoseveralrelatedcelltypes).</li></ul></li><li>Embryonicstem(ES)cells<ul><li>Derivedfromearlyembryo(upto 150cellsinembryostage);pluripotent,meaningtheycandifferentiateintomanycelltypes.</li><li>Consideredexcesssupplyfrominvitrofertilizationcontexts.</li></ul></li></ul><h3id="connectionsandrelevance">ConnectionsandRelevance</h3><ul><li>Foundationalprinciples<ul><li>Structure−functionrelationshipsareevident:membranecompositionaffectsfluidityandtransport,organelledistributionsupportsmetabolismandproteinprocessing,cytoskeletalnetworksdetermineshapeandtransportpathways.</li><li>Transportmechanisms(diffusion,osmosis,facilitateddiffusion,activetransport,vesiculartransport)underpinnutrientuptake,wasteremoval,andsignaling.</li></ul></li><li>Real−worldrelevance<ul><li>Understandingplasmamembranedynamicsisessentialforpharmacology(drugtransport),pathophysiology(membranedysfunction,junctiondisorders),andcellbiologytechniques(microscopy).</li><li>Mitochondrialfunctionanddynamicsrelatetoenergymetabolismanddiseases;lysosomalandproteasomalpathwaysarecentraltocellularqualitycontrolandcancerbiology.</li></ul></li><li>Ethical/philosophicalnotes<ul><li>StemcellplasticityandtheuseofEScellsinvolveongoingethicaldiscussionsaboutembryouse;iPScelltechnologyoffersalternativesbyreprogrammingadultcells.</li></ul></li><li>Keysymbolsandequationsusedinthisunit<ul><li>Membranecomposition(byfraction):</li><li></li></ul></li> <li><p>Basic cell concepts</p> <ul> <li>Cell components include:</li> <li>Plasma membrane</li> <li>Cytoplasm</li> <li>Cytoskeleton</li> <li>Organelles</li> <li>Inclusions</li> <li>Cytosol</li> <li>Nucleus is an organelle containing nucleoplasm.</li></ul></li> </ul> <h3 id="generalizedcellandorganellesfig2528">Generalized Cell and Organelles (Fig. 2.5, 2.8)</h3> <ul> <li>Generalized cell layout (apical, lateral, basal surfaces) with major organelles and structures:<ul> <li>Microvilli: plasma membrane extensions increasing surface area; often called brush border.</li> <li>Desmosomes and Hemidesmosomes: cell–cell and cell–basement membrane adhesions respectively.</li> <li>Secretory vesicle, Golgi vesicles, Golgi complex: involved in processing and shipping proteins.</li> <li>Rough endoplasmic reticulum (RER): studded with ribosomes; synthesizes phospholipids and proteins for plasma membrane, secretion, and lysosomes.</li> <li>Smooth endoplasmic reticulum (SER): detoxification in certain cells and steroid synthesis in others.</li> <li>Nucleus, Nucleolus, Nuclear envelope; various components shown in cross-section.</li> <li>Mitochondrion: site of ATP production.</li> <li>Cytoskeletal components: microfilaments, intermediate filaments, microtubules; provide structure and transport routes.</li> <li>Lysosome, peroxisome: organelles involved in digestion and reactive oxygen species management.</li> <li>Centrioles, Centrosome: organization center for microtubules during cell division.</li></ul></li> <li>Functional coordination<ul> <li>The plasma membrane, cytoskeletal framework, and organelles coordinate to maintain cell structure, transport, signaling, and metabolism.</li></ul></li> </ul> <h3 id="plasmamembranecompositionandproteins">Plasma Membrane Composition and Proteins</h3> <ul> <li>Membrane composition (Fig. 2.9, 2-11)<ul> <li>Phospholipids: ~75% of membrane lipids; form bilayer with hydrophilic heads facing aqueous environments and hydrophobic tails inward.</li> <li>Cholesterol: ~20%; modulates fluidity and stability.</li> <li>Glycolipids: ~5%; contribute to glycocalyx.</li></ul></li> <li>Membrane proteins types<ul> <li>Integral (transmembrane) proteins: span the membrane.</li> <li>Peripheral proteins: associated with membrane faces but do not span the bilayer.</li> <li>Glycoproteins: membrane proteins with carbohydrate chains; part of glycocalyx.</li></ul></li> <li>Membrane architecture<ul> <li>Phospholipid bilayer forms the structural foundation.</li> <li>Glycolipids and glycoproteins extend carbohydrate chains to the extracellular surface, forming glycocalyx.</li> <li>Cytoskeleton-associated proteins help anchor membrane and contribute to cell shape.</li></ul></li> <li>Functional roles of membrane proteins (Fig. 2.9)<ul> <li>Receptor proteins: receive signals from the environment or other cells.</li> <li>Enzymes: catalyze reactions at the membrane surface.</li> <li>Channel proteins: form pores that allow specific ions or molecules to pass.</li> <li>Transport proteins: move substances across the membrane.</li> <li>Cell-identity markers: identify the cell as self or non-self.</li> <li>Cell-adhesion molecules (CAMs): enable cells to attach to each other or to the extracellular matrix.</li></ul></li> <li>Membrane polarity and transport interfaces<ul> <li>Extracellular face and intracellular face of the membrane show distinct protein and lipid arrangements (Fig. 2.6b).</li></ul></li> </ul> <h3 id="membranetransportmechanisms">Membrane Transport Mechanisms</h3> <ul> <li>Filtration (Fig. 2.10a)<ul> <li>Capillary blood pressure forces water and small solutes through clefts between cells.</li> <li>Big solutes and blood cells are held back by the clefts (selective barrier).</li></ul></li> <li>Simple diffusion (Fig. 2.10b)<ul> <li>Lipid-soluble solutes diffuse directly through the phospholipid bilayer down their concentration gradient.</li> <li>Water-soluble solutes diffuse through channel proteins (pores) down their concentration gradient.</li> <li>Net movement from high to low concentration.</li></ul></li> <li>Osmosis (special case of diffusion)<ul> <li>Movement of water across a selectively permeable membrane from the more watery (higher water potential) to the less watery side.</li></ul></li> <li>Facilitated diffusion (Fig. 2.10c)<ul> <li>Solute binds to a receptor site on a high-affinity transport protein.</li> <li>Transport protein changes shape to shuttle solute across the membrane down its concentration gradient.</li> <li>Does not require ATP; driven by gradient.</li></ul></li> <li>Active transport (Fig. 2.10d)<ul> <li>Solute binds to receptor site on transport protein; ATP hydrolysis provides energy.</li> <li>Phosphate (P) binds to the protein, inducing a conformational change to move solute against its gradient.</li> <li>Requires cellular energy; can create or maintain concentration gradients.</li> <li>Typical schematic includes ATP → ADP conversion and P transfer to transporter protein.</li></ul></li> <li>Vesicular (bulk) transport (Fig. 2.11)<ul> <li>Pinocytosis (cell drinking): uptake of extracellular fluid and dissolved solutes via pinch-off vesicles.</li> <li>Receptor-mediated endocytosis: selective uptake of specific ligands bound to membrane receptors.</li> <li>Exocytosis: secretory vesicles fuse with the plasma membrane to release contents outside the cell.</li> <li>All involve vesicle formation, trafficking, and fusion to deliver cargo.</li></ul></li> </ul> <h3 id="surfaceextensionsandexternalfeatures">Surface Extensions and External Features</h3> <ul> <li>Microvilli<ul> <li>Plasma membrane extensions that increase surface area, enhancing absorption and signaling.</li></ul></li> <li>Cilia<ul> <li>Primary cilium: non-motile, sensory antenna for signaling pathways.</li> <li>Motile cilia: contain an axoneme of microtubules; move substances across cell surfaces.</li> <li>Axoneme structure: central microtubule core with dynein arms (motor proteins) driving bending.</li></ul></li> <li>Flagella<ul> <li>Long axoneme; primarily used to propel sperm cells.</li></ul></li> <li>Visual references<ul> <li>Figures 2.12a, 2.13 show microvilli, cilia, and axoneme structure.</li></ul></li> </ul> <h3 id="glycocalyxandcellularjunctions">Glycocalyx and Cellular Junctions</h3> <ul> <li>Glycocalyx<ul> <li>Carbohydrate-rich “fuzzy” coating on the extracellular side of the membrane.</li> <li>Functions: protection, cell identity, and binding to tissues.</li></ul></li> <li>Cellular junctions (Fig. 2.15)<ul> <li>Tight junctions: seal neighboring cells to prevent paracellular leakage.</li> <li>Desmosomes: resist mechanical stress by linking cytoskeletons of adjacent cells.</li> <li>Gap junctions: allow direct chemical communication between neighboring cells.</li></ul></li> </ul> <h3 id="thecellinteriorcytosolcytoskeletonandinclusions">The Cell Interior: Cytosol, Cytoskeleton, and Inclusions</h3> <ul> <li>Cytosol<ul> <li>Fluid portion of the cytoplasm, containing dissolved solutes and ions.</li></ul></li> <li>Cytoskeleton<ul> <li>Structural framework of the cell; determines shape; organizes contents; moves substances and sometimes the cell itself.</li> <li>Three main components:</li> <li>Microfilaments and terminal web (thin filaments): support cell cortex and help with movement.</li> <li>Intermediate filaments: provide tensile strength and structural integrity.</li> <li>Microtubules: provide routes for intracellular transport and form the mitotic spindle.</li></ul></li> <li>Organelles<ul> <li>“Little organs”; metabolically active; compartmentalize cellular contents for specialized functions.</li></ul></li> <li>Inclusions<ul> <li>Not essential for cell survival; stores cellular products or foreign matter.</li> <li>Examples: pigments, fat droplets, granules of glycogen; dust particles, viruses, and intracellular bacteria (nonmetabolic inclusions).</li></ul></li> </ul> <h3 id="thecytoskeletonindetailfig216">The Cytoskeleton in Detail (Fig. 2.16)</h3> <ul> <li>Roles of cytoskeletal elements<ul> <li>Protein filaments and tubules support cell structure, determine cell shape, organize cellular contents, move substances, and can drive cell movement.</li></ul></li> <li>Interaction map<ul> <li>Microfilaments, microtubules, intermediate filaments interact with organelles like lysosomes, mitochondria, nucleus, centrosome, and motor proteins (e.g., kinesin) to coordinate transport and organization.</li></ul></li> <li>Visual cues from figures:<ul> <li>Secretory vesicle in transport, desmosomes, microvilli, organelle distribution around the cytoskeleton, basal membrane context.</li></ul></li> </ul> <h3 id="organellesthefunctionalunitswithinthecellfig218219e">Organelles: The Functional Units Within the Cell (Fig. 2.18–2.19e)</h3> <ul> <li>Nucleus<ul> <li>Largest organelle; contains the cell’s chromosomes; genetic control center.</li> <li>Functions include production of ribosomes.</li> <li>Key components: nuclear envelope, nuclear pores, nucleoplasm, chromosomes, nucleoli.</li></ul></li> <li>Endoplasmic reticulum (ER)<ul> <li>“Little network within the cytoplasm” with cisterns.</li> <li>Rough ER (RER): studded with ribosomes; synthesizes phospholipids and proteins for the plasma membrane; proteins for secretion and lysosomes.</li> <li>Smooth ER (SER): detoxification in cells; synthesizes steroids in steroid-producing cells.</li></ul></li> <li>Ribosomes<ul> <li>Locations: cytosol, rough ER, nuclear envelope, nucleoli, mitochondria.</li> <li>Function: translate RNA into proteins; read mRNA and assemble amino acids into polypeptide chains.</li></ul></li> <li>Golgi complex<ul> <li>Consists of cisterns; receives transport vesicles from the RER; forms Golgi vesicles containing packaged proteins.</li> <li>Functions include lysosome formation, directing proteins to the plasma membrane or secretion via secretory vesicles.</li></ul></li> <li>Proteasomes<ul> <li>Cylindrical complexes that degrade and recycle damaged or unneeded proteins; degrade ~80% of a cell’s proteins.</li></ul></li> <li>Lysosomes<ul> <li>Contain enzymes in a single-unit membrane; clean up cell via autophagy (degrading organelles) and apoptosis (programmed cell death).</li></ul></li> <li>Peroxisomes<ul> <li>Similar to lysosomes; oxidize fatty acids and other organic molecules; produce hydrogen peroxide and degrade it with catalase; abundant in liver and kidneys.</li></ul></li> <li>Mitochondria<ul> <li>Powerhouses of the cell; specialized for aerobic respiration and ATP production.</li> <li>Structure: outer and inner membranes; cristae; mitochondrial matrix; contain mitochondrial DNA (mtDNA).</li></ul></li> <li>Centrioles<ul> <li>Composed of microtubules in a 9-triplet arrangement.</li> <li>Centrosome: cytoplasm region that contains the perpendicular pair of centrioles; important for organizing spindle during mitosis.</li> <li>Basal body: foundation for cilia and flagella.</li></ul></li> <li>Inclusions (nonessential structures)<ul> <li>Pigments, lipid or glycogen granules, and stored products; foreign materials like dust or bacteria can also accumulate as inclusions.</li></ul></li> </ul> <h3 id="thecellcyclegrowthreplicationanddivisionfigs239243">The Cell Cycle: Growth, Replication, and Division (Figs. 2.39–2.43)</h3> <ul> <li>Major phases<ul> <li>Interphase: growth, metabolic activity, and DNA replication.</li> <li>G1 (First gap phase): growth and normal metabolic roles.</li> <li>S (Synthesis phase): DNA replication.</li> <li>G2 (Second gap phase): growth and preparation for mitosis; DNA proofreading.</li> <li>Mitotic phase (M): division of nuclear material and cytoplasm.</li> <li>Prophase: chromatin condenses; nuclear envelope breaks down; nucleolus disappears; spindle fibers form and attach to kinetochores.</li> <li>Metaphase: chromosomes align at the cell center; asters attach to plasma membrane.</li> <li>Anaphase: centromeres split; sister chromatids pulled to opposite poles.</li> <li>Telophase: chromatids arrive at poles; chromosomes decondense; new nuclear envelope forms; nucleoli reform; mitotic spindle vanishes.</li> <li>Cytokinesis: division of cytoplasm; cleavage furrow forms; cell splits into two identical daughter cells.</li></ul></li> <li>Visual reference: Fig. 2.23 illustrates stages of mitosis with labeled structures (centrioles, chromatids, kinetochores, mitotic spindle).</li> </ul> <h3 id="stemcellsanddevelopmentalpotentials">Stem Cells and Developmental Potentials</h3> <ul> <li>Stem cells defined<ul> <li>Immature cells capable of developing into one or more mature, specialized cell types; possess developmental plasticity.</li></ul></li> <li>Adult stem (AS) cells<ul> <li>Present in most body organs; responsible for normal turnover and maintenance of tissue.</li> <li>Multipotent example: bone marrow cells (can differentiate into several related cell types).</li></ul></li> <li>Embryonic stem (ES) cells<ul> <li>Derived from early embryo (up to ~150 cells in embryo stage); pluripotent, meaning they can differentiate into many cell types.</li> <li>Considered excess supply from in vitro fertilization contexts.</li></ul></li> </ul> <h3 id="connectionsandrelevance">Connections and Relevance</h3> <ul> <li>Foundational principles<ul> <li>Structure-function relationships are evident: membrane composition affects fluidity and transport, organelle distribution supports metabolism and protein processing, cytoskeletal networks determine shape and transport pathways.</li> <li>Transport mechanisms (diffusion, osmosis, facilitated diffusion, active transport, vesicular transport) underpin nutrient uptake, waste removal, and signaling.</li></ul></li> <li>Real-world relevance<ul> <li>Understanding plasma membrane dynamics is essential for pharmacology (drug transport), pathophysiology (membrane dysfunction, junction disorders), and cell biology techniques (microscopy).</li> <li>Mitochondrial function and dynamics relate to energy metabolism and diseases; lysosomal and proteasomal pathways are central to cellular quality control and cancer biology.</li></ul></li> <li>Ethical/philosophical notes<ul> <li>Stem cell plasticity and the use of ES cells involve ongoing ethical discussions about embryo use; iPS cell technology offers alternatives by reprogramming adult cells.</li></ul></li> <li>Key symbols and equations used in this unit<ul> <li>Membrane composition (by fraction):</li> <li> ext{Phospholipids} = 0.75ofmembrane</li><li>of membrane</li> <li> ext{Cholesterol} = 0.20ofmembrane</li><li>of membrane</li> <li> ext{Glycolipids} = 0.05ofmembrane</li><li>Microscopicscaleunits:</li><li>of membrane</li> <li>Microscopic scale units:</li> <li>1 ext{ μm} = 10^{-6} ext{ m}$$
    • Typical cellular processes involve energy, gradients, and vesicular trafficking described qualitatively alongside the quantitative framework above.