Both structures maximize h bonding between peptides

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Unformatted text preview: nding between peptides that are in the bilayer, which is an energetically favorable outcome since there is no water present in the interior of the membrane. (d) You attempt to culture keratinocytes from these mutant mice and find that, unlike wild type keratinocytes, they don’t form a compact monolayer and detach from the cell 7.06 Spring 2004 PS 1 key 9 of 11 culture dish very easily. In an attempt to demonstrate that Epidermo-1 is involved in cellcell interactions at desmosomes you treat wild type keratinocytes with EGTA, a calcium chelator, and find that they detach from the dish just like the mutant cultures. Why does this occur? Desmosomes, adherens junctions, and tight junctions all need high concentrations of calcium to stay intact. EGTA is a calcium chelator and so removing the calcium from the culture media prevents the formation of these junctions and so the cells lose their adhesive properties and detach. 5. Below are five of the ways by which proteins can associate with the plasma membrane: (i) as a single-pass transmembrane protein (ii) as a multi-pass transmembrane protein (iii) via a covalent fatty acid chain (iv) via an oligosaccharide to phosphatidylinositol (v) as a peripheral protein via electrostatic interactions or a lipid binding domain (a) Give an example of each and detail the conditions by which you could purify each of these proteins from the cell membrane. Single-pass transmembrane protein: e.g. glycophorin A on erythrocytes or EGFR (epidermal growth factor receptor). Multi-pass transmembrane protein: e.g. bacteriorhodopsin, G-protein coupled receptors such as b-adrenergic receptor. Both single and multi-pass transmembrane receptors can be purified by adding detergent to cells to disrupt the membrane. Ionic detergents, such as SDS, will denature the protein and so prevent any functional assays being carried out. Non-ionic detergents, such as Triton X-100, can be used to purify these proteins in a non-denatured form. Covalent fatty acid chain: e.g...
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