10+–+membranes.2015 - membranes and pumps The lipid...

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membranes and pumps The lipid lamellar bilayer is composed of various amphipathic molecules – what are they – be able to recognize them – understand their chemistry – what do they all have in common/unique – membrane’s properties because of each What basic design options do integral membrane proteins have in common as far as their structure – what do we know about the movement of these proteins in the membrane? What are the various strategies that a cell uses to locate peripheral membrane proteins to the membrane surface? Types of pumps - generic structure and mechanism of passage / # of helixes, trans-membrane domain, regulatory piece, specificity – rates of transfer – explain why slow? – energy source for moving stuf
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2 Historical view of membrane structure has changed a lot membranes have 2x lipid within – RBC story not complex enough by self – so proteins were shown to be present freeze fracture showed peripheral and embedded varieties chemical labeling showed lateral movement of lipid and protein often rapid [but NOT always] Rafts of lipids move around each other, but non-raft lipids rarely join “old” raft Lipids not flipping leaflets / slow if occur
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3 advanced techniques demonstrate: Proteins can span membrane lipid anchors hold peripheral proteins in place cytoplasmic anchors can restrict motion of many integral proteins osmosis > Hypotonic/swell Hypertonic / shrink iso? Membranes have very little stretch – but very pliable / Suck into a capillary tube? little flipping occurs, much lateral movement impermeable to ions, polar/charged molecules water hydrates it bacterial lipid circumnavigates every few seconds small non-charged molecules can slip through slowly – H 2 O, gases, etc O of water tends to face the many + charged polar head groups, leaving ~positive H pointing out >>>>> thus membranes tend to repel cations.
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Techniques to monitor proteins 4 take home: some proteins move freely in lateral directions - often have GPI anchors diffuse intermittently [restricted part of time] = cadherins and transferrin - at times are connected to cytoskeleton immobile - all the time connected to something inside cell long distance directed movement - integrins moved via ? antibody labeling / fluorescent dyes bleach small part and watch difuse – FRAP fluorescence recovery after photo- bleaching label with gold particle and watch or force to move via optical trap
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8 Transmembrane Can you think of possible ways to hold here? Describe why they sit in membrane this particular way? Consider how proteins get placed in these locations . . . .
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9 Exoplasmic face/side Cytosolic face/side
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What kinds of lipids are found in membranes?
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