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TAMU BICH 410 - Membranes
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BICH 410 1st Edition Lecture 24Outline of Last Lecture I. Membrane StructureCurrent Lecture- Test info: know how mechanisms work that were gone over in class, should be able to compare membrane protein characteristics with globular and fibrous proteins- Proteins found on cytoplasmic side of membrane- Thioester- connects to membrane via cysteine- N-myristotyltransferase link is non-reversible and is a target for anti-parastitic drugs - Palmitoyl thioesterase- catalyzes reversible additions where protein participate in transmembrane signaling- GPI- phospholipid such as phosphotidyl inositol (modified sugar) with glycosylation and protein attachedo Always on outside of cell- extracellularly located- Lipid asymmetry- can have protein only on inside or only on outside same with lipidso More sphigomyeline on outside less inside - Lipid asymmetry- phospholipids are synthesized on or near interior of membraneo ATP dependent flippase- outer to innero ATP dependent floppase- inner to outer Both nonequilibrium distribution of phospholipidso Bidirectional scramlase- inner to outer in order to produce equilibrium distb- Temperature dependence of fluidity of a bilatero Below transition temp- bilayer becomes gel-like solid- solid order stateo Above transition temp- bilayer is liquid crystal- liquid order stateo Transition temp depends on chain length and degree of sat Increase in Carbon increase in melting point Increase in double bonds decrease in melting temp Cholesterol broadens temp range of phase transitiono As temp increases, increase in composition of long chain saturation fatty acidso As temp decreases, increase in composition of long chain unsaturation fatty acids- Membrane Rafts- lipids and protein laterally organized forming microdomains of liquid order stateso Protein rich in lipid aggregates that move in sea of phospholipidso High in sphingolipids and cholesterolo A number of transport and cell surface receptor proteins are associated with lipid rafto Many viruses associate w lipid raft and trigger import into cello Folate receptor is found on lipid raft; therefore fumonians toxins produced by fungi inhibit sphingosine synthesisThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Spinabifida outbreak in response to toxins- Barriers and fences cause lateral diffusion restricted by membrane skeleton o Membrane floats on cytoskeleton proteins such as spectrin and actin - Membrane skeletono Must anchor scaffold to membrane o Used in erythrocyteo Facilitates anchoring of membrane to skeleton Spectrin 75% of skeleton- composed of repeating segments that fold into 3 alphahelices - hereditary defect of spectrin- spherocytosis- RBC rapid turnover- Spectrin in RBC analogous to drystophan- defect causing muscular dystrophy Ankyrin associates with spectrin and HCO3-/Cl- anion channel- Membrane remodeling and curvature- most change shape in response to eventso Protein-lipid curvature occurs via: lipid imbalance, conical protein shape, helix insertion, interacting with scaffold proteins, cytoskeleton filaments- Caveolae- scaffolding proteins- flask shaped invagination associated with integral membrane proteins named cavelinso As it dimerizes it pulls and forms flasko Participates in endocytosis and intracellular signaling- Vesicle mediated transport- o Proteins, lipids, and other materials are constantly reorganized and exchangedo Normal processes require membrane fusion or budding and separation Cell division, exo-endocytosis, viral infection, organelles communicate via trafficking vesicleso Transmembrane orientation is preserved- meaning C and N terminus always conservedo Outside of cell is similar to inside of organelleo Vesicle fusion- requires integral and lipid linked proteins SNARES- R(arg) SNARES for vesicle and Q(glu) SNARE for the target Each helix has 7 pseudo residue repeats where and A and D are hydrophobic- similar to keratin structure R and 3Q H bond serving to bring helices into proper orientation for fusion Lumen goes to outside of cell when fusion occurs and SNARES are recycled backo Tetanus and Botulism Toxin- released by anaerobic bacteria Toxins are neurotoxins that inhibit the release of neurotransmitter Neurotoxins are 150KD polypeptides and are cleaved by host making a heavy and light chain- Heavy chain facilitates L chain- L chain cleaves target SNARE halting exocytosis of synaptic vesicleNEW UNIT- Membrane transporto Transport across membranes- diffusion from 1 side to next  The difference in conc of substance on 2 sides generates chemical potential- deltaG=RTn([Ad]/[As]) movement of ions generates electric potential= 2AFdeltapsi delta psi- measures potential across membrane- inside cell potential minus outside cell potential- negative number indicates inside of cell more negative than outsideo cytosol considered inside of


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TAMU BICH 410 - Membranes

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