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unit 4: membranes
BIOL 288
| Question | Answer |
|---|---|
| what are the membrane functions | boundary and permeability barrier, organization and localization of function, transport processes, signal detection, cell to cell communication |
| what is the Overton model (1890) | membranes are selectively permeable. lipids are present as coat on surface of cell |
| what is the Langmuir model (1905) | layered purified membrane phospholipids onto water. monolayer forms with hydrophilic head groups towards water and away from organic solvent |
| what is the gorter and Grendel model(1925) | estimated surface area of RBS and isolated their lipids, found 2X surface area of cell therefore membrane must be bilayrer |
| what is the Davson and Danielli model (1930-50) | proteins coat the lipid bilayer on both sides, polar pores account for selective permeability.. surface tension and solute permeability |
| what is the Robertson model(1960) | viewed membranes with electron microscope, all membranes have a trilaminar structure. pure lipid, diff protein;lipid ration, digestion with phospholipid, and organic solvemts for protein extraction |
| what is the Singer and Nicolson model(1972) | fluid mosaic model: proteins floating within the fluid lipid bilayer. globular proteins embedded in bilayer, and bilayer not rigid |
| what is teh Unwin and Henderson model (1975) | transmembrane proteins. integral with hydrophobic (transmembrane) and hydrophilic (linker) regions.. bacteriorhodopsin-7 transmembrane spanning segm,ents |
| Simons and van Meer (1988) and Ikonen(1997) | lipid rafts. membrane is heterogeneous containing regions called microdomains enriched in cholesterol, sphingolipids, and glycolipids. signaling molecules associated with the rafts |
| what are the components of the membrane | lipids(fluid part) and proteins |
| how to classify lipids based on head group | 1. phospholipids(a-phosphoglycerides,b-phosphoceramides)2. glycolipids. 3. sterols |
| how to classify lipids based on backbone | 1. glycerides. 2. ceramides. 3. sterols |
| what are phosphogylcerides | 2 FA+glycerol+phosphate with an R group(small polar group) |
| what is the bond between glycerol and fatty acid | ester bond, formed by dehydration |
| what are phosphoceramides | phosphate containing sphingolipids. |
| what is shingolipids | only membrane lipid that isn't phosphoglyceride. amino alcohol is backbone. FA attached to amino and phosphate attached to hydroxyl of sphingosine |
| what are glycolipids | cerebosides(neutral) and gangliosides (negative net charge due to sialic acid-amphipathic) surface markers are the carbs. CONTAINS: sphingosine+FA+single, uncharged sugar |
| what are the types of glycolipids | glycoglycerides(glycerol-based) and glycoseramides (sphingosine-based) |
| what are sterols | cholesterol and sitosterol (plants) up to 50% of membrane. rings are inside the hydrophobic region, rigidity. |
| what does the lipid bilayer characteristics other than structural support | each type of cell membrane has its own characteristic lipid composition. Lipid composition can influence numerous cell and biochemical functions. |
| How is the lipid bilayer : each type of cell membrane has its own characteristic lipid composition: | they differ from eachother in type of 1.head group 2.fatty acyl chain(length and degree of saturation) |
| what is the difference between saturated and unsaturated | saturated-most C-H bonds. unsaturated-has one or more double bonds |
| How is the lipid bilayer: lipid composition can influence numerous cell and biochemical functions including but not limited to; | cell-cell recognition(eg. ABO blood typing). activity of particular membrane proteins. physical state of the membrane(eg.fluidity), provide the precursors for highly active chemical messengers(eg. IP3 pathway). function in health and disease(eg. Tay-Sachs |
| what are the cell surface markers for ABO (gangliosides) | carbs; O is an H. A is an GalNac, and B is a Gal |
| see IP3 pathway slide | |
| see immune and inflammatory responses | |
| how to split the bilayer into Fracture face E (extracellular) and P(protoplasmic)-monolayers | flash freeze tissue, strike with diamond knife(path of least resistance through bilayer) |
| what can be seen from the striking membranes into monolayers | see pits and rough bumps |
| what are the three classes of membrane proteins | integral, peripheral, and lipid-anchored |
| what are the types of integral membrane proteins | monotopic protein, singlepass protein, multipass protein, multi-subunit protein |
| what are the types of peripheral membrane protein | peripheral membrane protein |
| what are the types of lipid-anchored membrane proteins | fatty acid/prenyl anchor and GPI anchor |
| what are the characteristics of integral proteins | amphipathic, one or more hydrophobic regions, can have hydrophilic domains. often alpha helical. can have beta-barrels |
| what are examples of integral | cyclooxygenases(COX1 & 2). integrins(signal transduction), Rhodopsin,porins(7pass, beta-barrel), and insulin receptor |
| what are the characteristics of peripheral proteins | entirely outside of membrane(intra or extra), weak electrostatic forces/H bonds, disulfide bonds. can be enzymes involved in signal tranduction. coat cell. factors that transmit between transmembrane proteins |
| what is the insulin receptor | heterotetramer. has alpha regions(glycoproteins) and B-single pass transmembrane |
| what are the interactions with peripheral proteins | connect to integral proteins , and polar head of bilayer |
| what are the characteristics of lipid-anchored protiens | can be located on either side of membrane(peripheral) and covalently bound to lipid in bilayer(integral). inner surface made in cytosol and post-transitionally modified |
| what are the types lipid-anchored proteins | myristic acid, palmitic acid, (fatty acid)farnesyl, geranylgeranyl(pernyl) |
| what is myristic acid | 14C. joins protein at amino terminus via amide bond. saturated |
| what is palmitic acid | 16C attached at cysteine residue. thioether bond. saturated |
| what is farnesyl | 15Cthioether |
| what is geranylgeranyl | 20C built from several prenyl groups put together. thioether |
| what is glycosylphosphatidylinositol | outer monolayer GPI-anchored protein |
| how is glycosylphosphatidylinositol made | in ER lumen is made and attachs to membrane, then cleaved by GPI transmidase and moves to another GPI anchor to make mature GPI-linked protein |
| What is on the outer layer | sphingomyelin, phosphatidylcholine, glycoproteins/lipids, some monotopic/peripheral proteins |
| what has equal dist between inner and outer layer | cholesterol |
| how is membrane assymetry formed | in ER-Golgi-sent to PM. in ER(adds phopholipids, scramblase makes symmetrical. in golgi(flippase makes the proper proteins on each side-assym) |
| what makes a liquid(fluid) to solid (crystalline gel) of lipid | transition temperature |
| what is liquid (fluid) lipid | 37C. parellel. can rotate, move laterally |
| what is solid(crystalline gel) lipid | FA chain movement restricted and not straight |
| what are the factors affecting transition temperature | degree of saturation, fatty acid chain length, and sterols(cholesterol) |
| what does a higher degree of saturation mean | higher # double bonds, and lower TT |
| what does shorter chain length mean | more fluid and lower TT |
| what do sterols do to the membrane? | decreases fluidity at high temps(vice versa); is fluidity buffer. 1. increases durability.2.dec fluidity3. dec permeability |
| what is the importance of membrane fluidity | perfect compromise between a rigid, ordered structure and a totally fluid, nonviscous liquid. |
| what are the functions that depend on this compromise between structue and fluidity | 1. interactions that take place within the membrane.2. membrane assembly.3. cell movement and growth. 4. exo and endocytosis |
| what is the interactions that take place within the membrane | clustering of membrane proteins to form: intercellular junctions, photosynthetic complexes, and synapses |
| how do cells maintain membrane fluidity | 1.enzymes remodel membrane to keep them fluid. 2. change phospholipid synthesis |
| what are the enzymes that remodel membranes to keep them fluid | a) desaturase enzymes to convert single bonds to double bonds and move with kinks. b)shuffling of fatty acyls chains-phospholipases (cut off chain)and acyltrandferases(move other chain into cleaved) |
| homeotherms vs. heterotherms maintain membrane fluidity | homeo-maintain temp, hetero-influenced by environment changes by regulating memb fluidity |
| what are the movements of a dynamic membrane | flex, lateral shifts, transverse diffusion(flip-flop) |
| what is transverse diffusion | movement. flip-flop. takes a realy long time, and flippase enzyme speeds up |
| what are the methods to measure protein mobility | cell fusion, and FRAP |
| how cell fusion to measure protein mobility | takes two cells, fuses them with a virus, and adds antibodies to label the lipids, and note that after 40 minutes the membranes are diffused equally throughout the fused cell |
| how FRAP to measure protein mobility | fluorenscence recovery after photobleaching: take cell, and label cell surface molecules with fluorence, and lazer out a section, and over time the fluorsecnce will return as proteins move back |
| what molecules move the most into the cell | small inorg/org and ions |
| what are the small organic molceules | sugars, amino acids, etc |
| what are the small inorganic molecules | 02, CO2, NO, H2O |
| what are the ions | Na, K, Ca, Cl |
| what are the movements across membranes | 1, simple diffusion directly through bilayer.2. simple diffusion via protein-lined channel,3.facilitated diffusion via a transporter protein.4. acitve transport |
| what are the types of active transport | indirect and direct |
| what is direct active transport | transporter protein hydrolyzes energy source-ATP |
| what is indirect active transport | energy used to establish a gradient, made by transport proteins. are symporter(Na/glucose) and antiporter(na/k) |
| what are the energy independent movements | 1, simple diffusion directly through bilayer.2. simple diffusion via protein-lined channel,3.facilitated diffusion via a transporter protein. |
| what is direct diffusion | spontaneous process-molecules move down gradient to eliminate difference between the two areas-reaching equilibrium, follows 2nd LAT |
| what is electrochemical gradient | conc+ele potential gradient |
| what do uncharged molecules move doen | conc gradient |
| what do charged molecules move down | electrochemical gradient |
| what is entropy | the degree of randomness/disorder in a system, molecules want to eliminate free energy, so they spread apart |
| what is free energy | G. the amount of energy available to do work |
| what are the types of direct diffusion | diffusion of charged and uncharged molecules |
| what is the diffusion of uncharged molecules | only concerned with concentration gradient, movement from high conc across memb to low conc until reach equilibrium. free energy depends on magnitude of conc difference |
| what is the diffusion of charged molecules | must consider both concentration and memb potential. typical membrane potentials (reflects charge on the inside of the cell) |
| what is the memb potentials for animals, bacteria and plants | animals;-60 to -90mV. bacteria-150mV. plants-200 to -300 mV |
| what does neg memb potential favour | inward flux of cations becuase its neg. |
| calculate free energy | |
| what does diffusion rate depend on | size, polarity, |
| how does size affect diffusion rate | becuase smaller diffusion thru memb faster and in some cell water enters via antiporins. |
| what is the memb highly permeable to | oxygen, water, carbon dioxide and nitric oxide |
| how does polarity affect diffusion rate | estimated using partition coeffient, ratio of soluability in nonpolar solvent vs. water, the greater the lipid soluability the fater the rate of diff |
| what is memb diffusion usually | permenale to small, nonpolar molecules, and poorly permeable to large polar(sugars, AA) and ions |
| hwo diffusion via a protein chaneel | PM highly impermeable to ions so channels provide mechanism for their transport. integral memb proteins that surround an aqueous pore . most are selective. move down electrochemical graient. most ion channels are GATED |
| what are the types of gated channels | voltage-gated(difference in ionic charge) , ligand-gated(binds of ligand that doesnt cross), and mechano-gated(stretch or tension of memb) |
| what are the components of bacterial KcsA K+ channel | 1. each subunit has two membrane spanning domains. m1 and m2 alpha helicases2. has "p" pore region= short helix and non-helical loop that extends 1/3 of channel. |
| what is the nonhelical loop | form lining of selectivity filter, only allows k+ to pass. |
| what does the bacterial KcsA K+ channel consisit of | 4 identical proteins(homotetramer) |
| how does bacterial KcsA K+ channel filter work | GYGVT forms oxygen ring, created from carbonyl oxygen of peptide backbone(1-4) the 5th oxygen is from thronine. each ring has 3A |
| why only K+ throughbacterial KcsA K+ channel | because it is stabilized from hydration shell in the filter and fits 2.7A |
| How does K+ move through the channel | through 1,3 and 2,4 one at a time and is stabilized by 4+4 oxygen =8O2 box. no energy barrier of the system |
| how does the bacterial KcsA K+ channel gate open and close | selective filter is rigid, and the open and close based on M2 proteins is pH-mediated!! low pH causes M2 proteins to flex at the glycine residue. when closed hydrophobic residues keep it blocked |
| what are the similarities between eukaryotic voltage-sensing K+ channel and the bacteria KcsA K+ channel? | both homotetramers. (euk is 6 helices, not 2), same filter structure as bact) |
| what is the differences between eukaryotic voltage-sensing K+ channel and the bacteria KcsA K+ channel? | euk- 6 helices, not 2. euk true voltage-gated, not pH. euk has pore domain and cytoplasmic domain made up of b-chain) |
| what is the AA structure of the K+ channels filters | Gly-Tyr-Gly-Val-Thr |
| what are the three different states of the K+ euk filter | rest, open and inactivated |
| what are the stages of an action potential | resting, depolarization, rising phase of action potential, falling phase of the action potential, undershoot |
| what is the resting phase | resting potential -70mV, there is way more Na outside than inside. way more potassium inside than outside |
| what is the depolarization phase | electrical stimulus, sodium comes in. AP starts at threshold |
| what is the rising phase of action potential | sodium flows in, rapid depolarization, inside more positive than outside |
| what is the falling phase of the action potential | sodium channels close (S4 detects changes and conformational change due to repel b/c it is positive and inside now and moves towards pH. transmits to S5-S6 where the kink region is "P-V-P" hinge . potassium leaves cell |
| what is the helix breaker | proline |
| what is the overshoot phase of the action potential | below memb potential, inactivated peptide blocks potassium channel. rest phase |
| how do action potential propagate | movement of charges change the membrane potential. saltatory conduction |
| what is saltatory conduction | myelin sheath covers axon, leaves nodes of Ranvier where the AP jumps to which increases transmission speed |
| what is myelin sheath | lipid rigid, isolator, AP cant pass through |
| what is facilitated diffusion | no energy, protein mediated movement (carrier protein, transporter, permease) with electrochemical gradient. changes protein conformation, but no energy |
| what are the steps in facilitated diffusion | binding on one side, conformational change, and release on the other side |
| facilitated diffusion points on transporter | specific (1 molecule), saturation kinetics(limit of transporting by # of proteins), competitive inhibition(can't transport more than one molecule at same time) |
| what are the glucose transporters | bidirectional, with electrochemical gradient. 6 hexose=6 C sugars. 12 transmembrane protein(crosses 12 times), distribution are tissue specific |
| what are the insulin independent | GLUT 1,2,3 |
| what are insulin dependent | GLUT 4 |
| what are the steps in insulin dep GLUT | insulin-insulin receptor-GLUT 4 translocation to the membrane |
| a low affinity transporter= | high abundance of glucose |
| what are the steps of a general GLUT indep of glucose | 1. glucose binds to binding site open to the outside. 2. transport protein shifts to alternative confromation.3. glucose released to the inside.4. transport protein returns to its original conformation. the glucose inside gets phosphate added |
| why add phosphate to glucose | so that the conc of glucose remains higher on the outside of the cell. it gets phosphorylates |
| what is active transport | transport against electrochemical gradient, requires energy input |
| what are the key functions of active transport | 1. uptake & concentration of essential nutrients, 2. excretion of waste & secretion of key molecules out of the cell. 3. maintenance of steep ion gradients that are essential for life |
| what are the key points on active transport pumps | 1. involves specific membrane proteins, "pumps" that are specific for 1/few molecules. 2. most pumps have directionality (uni). some are reversible are coupled to ATP synthesis(create energy as molecules move down gradient) |
| what is direct active transport | movement is coupled to a reaction that produces energy, usually ATP |
| what is indirect active transport | transport of one molecule against its gradient is coupled to the movement of one molecule down its. symport and antiport |
| what are symporter | molecules move in same direction |
| what are antiporter | molecules move in opposite direction |
| what are the 4 types of transport ATPases | P-class pumps, V-class proton pumps, F-class proton pumps, ABC superfamily |
| what is P-class pumps | reversible, phosphorylated by ATP. 8-10 transmemb protein, transport cations. sensitive to vandate (vo43-).eg=NA+/K+ and H+/K+ ATPases |
| what is V-class proton pumps | on vacuole/lysozymes. 2 multisubunit components, v1- peripheral cytoplasmic component that gets phosphorylated by ATP |
| what is F-class proton pumps | "factor", inner mito memb and chloroplast. 2 multisubunit components. f1-peripheral. protons move down conc grad. ATP binding site, can synthesize it via ATPase via proton movement b/c proton pore moves w/ grad. can pump other dir using ATP BIDIRECTIONAL |
| what is ABC superfamily | 150 transporters. ATP binding cassette. 4 proton domains. 2 integral(t)-hydrophobic,6 transmemb, form channel. 2 peripheral(a)-bind ATP. heterotetramer. move ion, sugars, AA. medically relevant. |
| How NA+/K+ ATPase pump direct active transport | initial state: pump open to inside E1), 3 Na+ move taken from inside, ATP phosphorylates alpha subunit, confrom change expels 3 Na+ outside. pump open outside-E2), two K+ from outside, dephosph con change, 2K+ put inside return to initial state |
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