Transcript Cell Size
Chapter 4 A Tour of the Cell Cytology: science/study of cells • Light microscopy resolving power = measure of clarity • Electron microscopy TEM = electron beam to study cell ultrastructure SEM = electron beam to study cell surfaces • Cell fractionation = cell separation; organelle study • Ultracentrifuges = cell fractionation; 130,000 rpm • \ Cell Types: Prokaryotic • Nucleoid: DNA concentration • No organelles with membranes • Ribosomes: protein synthesis • Plasma membrane (all cells); semi-permeable • Cytoplasm/cytosol (all cells) Cell Size • As cell size increases, the surface area to volume ratio decreases • Rates of chemical exchange may then be inadequate for cell size • Cell size, therefore, remains small Range of Cell Size Cell Fractionation Nucleus • Genetic material... •chromatin •chromosomes •nucleolus: rRNA; ribosome synthesis • Double membrane envelope with pores • Protein synthesis (mRNA) Ribosomes • Protein manufacture • Free - cytosol, proteins function in cell • Bound - endoplasmic reticulum, membranes, organelles, and export Compartmentalization • Increases internal surface area • Sometimes enzymes are incorporated into the membrane. • Provide localized environmental areas. • Sequester reactions (hydrolytic enzymes in lysosomes) The Endomembrane System • Membranes may be interrelated directly or indirectly via vesicles. • Membranes are dynamic structures. • • • • • • Nuclear Envelope Endoplasmic Reticulum Golgi Apparatus Lysosomes Vacuoles Plasma membrane (not actually a member of the system, but related to it). 1. Endoplasmic Reticulum (ER) Continuous with nuclear envelope • Smooth ER •no ribosomes •synthesis of lipids •metabolism of carbohydrates •detoxification of drugs and poisons Stores Ca2+ ions • Rough ER •with ribosomes; •synthesis of secretory proteins (glycoproteins), membrane production Rough ER Ribosomes 1. Rough ER ribosomes synthesize secretory proteins 2. Growing polypeptide is threaded through the ER membrane into the lumen or cisternal space 3. Protein folds into its native conformation 4. Local enzymes catalyze covalent bondingmodifications 5. Protein departs in a transport vesicle 2. Golgi Apparatus • • • • ER products are modified, stored, and then shipped Cisternae: flattened membranous sacs trans face (shipping) & cis face (receiving) Transport vesicles 3. Lysosomes • • • • • Sac of hydrolytic enzymes; digestion of macromolecules Phagocytosis Autophagy: recycle cell’s own organic material Tay-Sachs disease - lipid-digestion disorder Apoptosis 4.Vacuoles • Membrane-bound sacs (larger than vesicles) • Food vacuole (phagocytosis) • Contractile (pump excess water) • Central vacuole (storage in plants) • Tonoplast (membrane) Relationships Among Endomembranes Other Membranous Organelles • Not part of endomembrane system • Peroxisomes • Mitochondria • Chloroplasts Peroxisomes • Single membrane • Produce hydrogen peroxide in cells • Metabolism of fatty acids; detoxification of alcohol (liver) • Hydrogen peroxide produced, then converted to water – action of catalase. Mitochondria • quantity in cell correlated with metabolic activity; • cellular respiration; • double membranous (phospholipid); • cristae/matrix; • intermembrane space; • contain own DNA • bacterial origin Chloroplasts • type of plastid; • thylakoids (flattened disks) • stroma; • double membranous; • grana (stacked thylakoids); • own DNA The Cytoskeleton • • Fibrous network in cytoplasm Support, cell motility, biochemical regulation • Microtubules: thickest; tubulin protein; shape, support, transport, chromosome separation • Microfilaments : thinnest; actin protein filaments; motility, cell division, shape • Intermediate filaments: middle diameter; keratin; shape, nucleus anchorage Tubulin in endothelial cell Motor Molecules and the Cytoskeleton a. motor molecules on one microtubule ‘grab’ and slide past another microtubule. b. motor molecules attach to receptors on organelles such as vesicles, enabling them to ‘walk’ along the microtubule Centrosomes/centrioles • Centrosome: region near nucleus • Centrioles: 9 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 • 2 single microtubules in center • connected by radial spokes • anchored by basal body • dynein protein a. ls. cilium b. cs cilium, showing 9+2 arrangement c. cs basal body, anchors the cilium to the cell – third microtubule incorporated (centriole) central 2 lost How Dynein ‘walking’ Moves Cilia and Flagella The dynein arms of one doublet grip the adjacent doublet. Powered by ATP Microfilaments and Motility Cell Surfaces & Junctions • Cell wall: not in animal cells protection, shape, regulation • Plant cell: primary cell wall produced first middle lamella of pectin (polysaccharide); holds cells together • Some plants: a secondary cell wall; strong durable matrix; wood (between plasma membrane and primary wall) Extracellular Matrix (ECM) Glycoproteins: proteins covalently bonded to carbohydrate Collagen (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 Junctions • PLANTS: • Plasmodesmata: cell wall perforations; • water and solute passage in plants • ANIMALS: • Tight junctions: fusion of neighboring cells; prevents leakage between cells • Desmosomes: riveted, anchoring junction; strong sheets of cells • Gap junctions: cytoplasmic channels; allows passage of materials or current between cells Plamodesmata in a thin plant section Intercellular Junctions in Animals The Lives of a Cell Harvard Animation • http://aimediaserver.com/studiodaily/videop layer/?src=harvard/harvard.swf&width=640 &height=520 Narrated version Assignment http://www.bu.edu/histology/m/t_electr.htm Choose 4 images to draw and label