Ch. 3 Cells

Ch. 3 Cells!IntroductionCell theoryCells are the smallest living subunit of an organismAll cells arise from pre-existing cellsBacteria, amoebas are unicellular and function independentlyHuman cells work interdependentlyVary in size, shape, functionMostly microscopicMore than 200 kindsCell StructureCell membrane (plasma membrane)Forms outer boundary of cellNucleusAbsent in mature red blood cellsCytoplasmOrganellesCell MembranePlasma membrane (PM)Made of phospholipids, cholesterol, proteins (Fig. 3-1)Phospholipid bilayerPermit lipid-soluble materials to enter/leave cell via diffusionCholesterol makes membrane more stableProteinsForm channels or pores to permit passage of materialsCarrier enzymes (transporters) help substances enter cellAntigens identify cells as selfReceptor sites for hormones

Cell Membrane (cont.)Active, dynamic membraneSelectively permeableCertain substances can pass through, others cannot

NucleusWithin cytoplasmBounded by 2-layered, porous nuclear membraneContains 1 or more nucleoli, chromosomes (Fig. 3-2)Nucleolus small sphere of DNA, RNA, proteinForm ribosomal RNA (rRNA); becomes part of ribosomes; involved in protein synthesisNucleus (cont.)Control centerContains 46 chromosomes in long threads called chromatinBefore cell division, chromatin coils into visible chromosomes (made of DNA, protein)Nucleus contains the same genetic information, but only a small number of genes are active switched onActive genes code for proteinsCytoplasmWatery solution of minerals, gases, organic molecules, organellesCytosolWater portion of cytoplasm; where many rxns take placeOrganellesIntracellular structures, often membrane-boundHave specific functions in cell metabolism (Fig. 3-2)Endoplasmic reticulum (ER)Extensive tubular network extending from nuclear membrane to PMRough ER has ribosomes on surface, smooth ER does notPassageway for proteins, lipidsOrganelles (cont.)RibosomesNot membrane-boundVery small structures made of protein and rRNASome on Rough ER, others in cytoplasmSite of protein synthesisOrganelles (cont.)Golgi apparatus (GA)Flat, membranous sacs stacked on top one anotherCarbohydrate synthesis, packaging for secretion from the cell

Organelles (cont.)Golgi Apparatus SecretionSmall sacs of Golgi membrane break off & fuse with PMSubstance is released to cell exterior (exocytosis)Organelles (cont.)MitochondriaOval or spherical organelles bounded by double membraneInner membrane has folds (cristae)Site of ATP productionContain own genes in a single DNA moleculeDuplicate themselves when cell dividesMany mitochondria in muscle cellsOrganelles (cont.)LysosomesSingle-membrane digestive structuresHave enzymes that digest bacteria, old cell parts and dead cellsOrganelles (cont.)CentriolesPair of rod-shaped structures just outside the nucleusOrganize spindle fibers during cell divisionCiliaShort, hair-like structures covering surface of cellBeat in unison and sweep materials across cells surfaceCilia in fallopian tubes sweep egg toward the uterusFlagellaWhip-like tailProvides motility for spermOrganelles (cont.)MicrovilliFolds of cell membrane on the free surface of a cellGreatly increase surface area of membranePart of cells lining organs that absorb materialSmall intestineKidney tubulesTable 3-1

Cellular Transport MechanismsEnable cells to move materials into or out of cellDiffusionOsmosisFacilitated diffusionActive transportFiltrationPhagocytosisPinocytosis

DiffusionMovement of molecules from an area of high to low concentration along a concentration gradientOxygen and CO2 move by diffusion (Fig. 3-3)

OsmosisDiffusion of H2O through a selectively permeable membraneWater moves from an area with more to an area with less waterWater will move to an area with more solutesIf a 2% salt solution and a 6% salt solution are separated by a membrane, allowing only water to pass through, in which direction will water diffuse?See Box 3-1Facilitated DiffusionMolecules move through a membrane from an area of high to low concentration with assistanceUse a carrier enzyme (transporter)Active TransportRequires ATP to move molecules from a low to high concentration against a concentration gradientNerve and muscle cells have sodium pumps to move sodium ions out of cells (Fig. 3-3)FiltrationRequires energy of mechanical pressureWater, dissolved materials are forced through a membrane from an area of high to low pressureFormation of tissue fluid; first step in urine formationPhagocytosis & PinocytosisForms of endocytosisPhagocytosisWhite blood cell engulfs bacteria (Fig. 3-3)Digestion using enzymes in lysosomesPinocytosisStationary cells take in small molecules adsorbed or attached to their membranesKidney tubules reabsorb small proteins (Fig. 3-3)Table 3-2Cell DivisionProcess by which cell reproduces itself2 typesMitosisMeiosis

MitosisOne cell with a diploid (2N) # of chromosomes divides into 2 identical cells, each with the diploid number2N = 46InterphaseDNA replication enables each chromosome (chromatin) to copy itselfResting (non-dividing) stageStores energy in ATP

Mitosis (cont.)Long, thin, invisible chromatin begins to coilEach looks like a letter X because original DNA molecule & its copy (chromatids) are attachedMitosis stages (PMAT); see Table 3-4; Fig. 3-5ProphaseMetaphaseAnaphaseTelophase

Mitosis (cont.)Essential to replace damaged or dead cellsOccurs constantly in epidermis, stomach lining, red bone marrowDoes not occur in most muscle cells & neuronsSkeletal muscle cells have limited mitosisResearch has found some potential for mitosis in the CNS and heartAt present, mitosis does not take place sufficiently enough to replace dead cells

MeiosisMore complexResults in gamete (egg, sperm) formationOne diploid cell (2N) divides twice to form 4 haploid cells (N)Meiosis takes place in ovaries (oogenesis) and testes (spermatogenesis)reduction divisionDuring fertilization, the egg joins with the sperm to restore the diploid number of 46 in the fertilized egg (zygote)