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Final Exam Study Notes

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University of Guelph
BIOL 1090
Wright& Newmaster

Two classes of cells 1. Prokaryotic – bacteria; structurally simpler; don‟t have membrane- bound organelles 2. Eukaryotic – protists, fungi, plants, animals; more complex; membrane-bound organelles Nuclear Pore Complex  Enables movement of molecules into and out of nucleus Cytoskeletal Elements (actin & intermediate filaments, microtubules)  Contribute to cell shape; supports structure, transport of material Viruses  Non-cellular macromolecular packages; can function and reproduce ONLY within living cells  Outside of cells = virion (inanimate particle - inactive) – comprised of small amount of DNA or RNA (encoding a few to hundreds of genes), protein capsule = capsid, does not have a nucleus  Bind to cell surface via specific proteins then enter cell – this defines the cell types the virus can infect and host range  When inside cell, utilized cellular machinery to synthesize nucleic acids and proteins – assembles new virus particles  Two types of viral infection 1) Lytic – production of virus particles ruptures, kills cell 2) Non-lytic (Integrative) – viral DNA is inserted in host genome = provirus; viral progeny bud at cell surface; cell can survive, often w/ impaired function – cell can still survive, but does not function properly Plasma Membrane ONLY  Cell boundary  Control movement of material into/out of cell  Allow response to external stimuli  Enable interactions b/w cells  Provide scaffold for biochemical activities including energy transduction Biological Membranes  Bilayer of amphipathic lipids  Proteins – integral (trans membrane proteins span the lipid bilayer), peripheral (membrane proteins associate with the outer surfaces of the lipid bilayer), lipid-anchored (proteins are covalently attached to a lipid in the bilayer, prion protein)  Asymmetrical – two leaflets have distinct lipid composition; outer leaflet = glycolipids, glycoproteins (lipids, proteins with carbohydrate attached)  Lipids move easily, laterally within leaflet  Lipid movement to other leaflet = slow, not easy  Membrane proteins can diffuse within bilayer –movement of proteins is restricted; some don‟t move; rapid movement = spatially limited; long range diffusion = slow; biochemical transduction can dramatically alter protein‟s mobility in the membrane;  Dynamic! Fluid-Mosaic Model  Hydrophobic – alpha helix Membrane Fluidity  Determined by temp & type  Saturated ↓ fluidity  Unsaturated ↑ fluidity  ↑ temperature, ↑ fluidity = liquid crystal  ↓temp, ↓ fluidity = crystalline gel  “Jell-O”  Balance allows mechanical support; flexibility; dynamic interactions b/w membrane components; membrane assembly, modification; ordered = rigid, disordered = flexible (relate to a person)  Must be maintained; in response to temperature change, lipid composition can be changed by 1) desaturation of lipids 2) exchange of lipid chains  Regulated by cholesterol – alters packing and flexibility of lipids; if added to a liquid crystal membrane, fluidity will decrease; if added to a crystalline gel membrane, fluidity will increase; Lipid rafts  Small areas of PM enriched in certain types of lipids  Relatively rigid  Some membrane proteins accumulate in rafts  May form „functional compartment‟  High in cholesterol Ion Channels  Formed by integral membrane proteins that line an aqueous pore  Selective, allowing only one type of ion to pass  Ions move down concentration gradient  Often „gated‟ (can be opened or closed) Types of Gated Channels 1. Voltage-gated Channels (eg. K+ channel) – channel responds to change in charge across membrane – move down gradient, non- passive, mediated 2. Ligand-gated Channels (eg. CFTR) – channels responds to binding of specific molecule (the „ligand‟ – an ion or molecule that binds to another, usually larger, molecule (metal)) 3. Mechano-gated Channel (eg cation channels in inner ear) – channel responds to physical force on membrane (eg stretch) FOUR WAYS MOLECULES CROSS MEMBRANES: Simple Diffusion  Very small molecules  Uncharged  Down a concentration gradient (flow is „downhill‟)  Eg. O2, CO2, H2O (osmosis)  Passive, non-mediated Diffusion through a Channel  Small, charged molecules (ions)  Down a concentration gradient  Eg. Na+, K+, Ca2+, Cl-  Passive, non-mediated  Channels - Facilitated Diffusion  Compound binds specifically to integral membrane protein called „facilitative transporter‟  Change In conformation of transporter allows compound to be released on other side of membrane  Compound moves down concentration gradient  Ex. Glucose transporter  Passive (doesn‟t require energy), mediated (requires something else to get through, needs to bind to something) Active Transport  Compound binds specifically to integral membrane protein called „active transporter‟  Change in conformation of transporter allows compound to be released on other side of membrane  Compound moves up concentration gradient = takes more energy to swim up river than it does to swim river  Requires input of energy  The Na+/K+ ATPase mains cellular [Na+] and [K+] using ATP (transporter responsible for maintaining cellular concentrations of Na+ and K+; 3Na+ bind to the transporter inside the cell; Phosphate is transferred from ATP>the transporter, transporter changes conformation; Na+ is released outside the cell; 2K+ bind to the transport outside of the cell; phosphate group is lost, transporter changes conformation, releasing K+ inside the cell;)  Only active one that requires energy Movement of Substance across Cell Membranes  Lipid bilayers do not allow many compounds to pass through them freely  Small, uncharged molecules cross membranes relatively easily (O2, CO2, NO, H2O)  Large, polar, charged compounds cannot easily cross lipid bilayers  Specific mechanis
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