Chapter 6B

A Tour of the Cell

Other Membranous Organelles, I

Mitochondria - quantity in cell correlated with metabolic activity (the more active, the more mitochondria)Site of cellular respirationDouble membranes (phospholipid); cristae/matrixIntermembrane spacecontain own DNA

Other Membranous Organelles, II

Chloroplast - type of plastidDouble membranousThylakoids (flattened disks)Grana (stacked thylakoids)Stroma – gel like material around granaPhotosynthesisOwn DNA

Peroxisomes

Single membraneProduce hydrogen peroxide in cellsMetabolism of fatty acids; detoxification of alcohol (liver)Hydrogen peroxide then converted to water by catalase

The Cytoskeleton

Fibrous network in cytoplasmSupport, cell motility, biochemical regulationMicrotubules - thickest; tubulin protein; give shape, support, transport, chromosome separationMicrofilaments - thinnest; actin protein filaments; motility, cell division, shapeIntermediate filaments - middle diameter; made of keratin protein; shape, nucleus anchorage

Centrosomes/CentriolesCentrosome - region near nucleus containing the centriolesCentrioles - nine sets of triplet microtubules in a ring; used in cell replication; only in animal cells

Cilia/flagella

Locomotive appendages Ultrastructure: “9+2” 9 doublets of microtubules in a ring with 2 single microtubules in center Connected by radial spokes Anchored by basal body Made of dynein protein

Cell surfaces & junctions

Cell wall – in plant, not animal cells Protection, shape, regulationPlant cell: Primary cell wall produced first Middle lamella of pectin (polysaccharide); holds cells together In some plants, a secondary cell wall forms; strong durable matrix; wood (between plasma membrane and primary cell wall)

Extracellular matrix (ECM)Glycoproteins - proteins covalently bonded to carbohydrateCollagen (50% of protein in human body); embedded in proteoglycan (another glycoprotein-95% carbohydrate)Fibronectins - bind to receptor proteins in plasma membrane called integrins (cell communication)

Intracellular junctionsPLANTS:Plasmodesmata: cell wall perforations; water and solute passage in plantsANIMALS:Tight junctions: fusion of neighboring cells; prevents leakage between cellsDesmosomes: riveted, anchoring junction; strong sheets of cells Gap junctions: cytoplasmic channels; allows passage of materials or current between cells