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Lecture 4

Lecture 4- membrane proteins.docx

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University of Ottawa
Kathleen Gilmour

Lecture 4 - Topic 2 (membrane proteins) last lecture highlights -amphipathic nature of phospholipids key to bilayer structure (hydrophobic interactions) and allows it to function as a permeability barrier. -membrane also contains significant amounts of sterols (except in prokaryotes; 4-ring hydrocarbon skeleton with hydrophobic tail and hydroxyl group) and small amounts of glycolipids (glycerol or sphingosine backbone with carbohydrate replacing phosphate R-group; function as signals) Pop quiz: 1.what type of non-covalent interactions is of critical importance in determining membrane structure? A: hydrophobic, hydrophilic, these types of interactions hold membrane together 2.what membran in a eukaryotic cell might be expected to lack sterols? why? A: mitochondria are thought to have come from prokaryotes, and they lack sterol, so the inner mitochondrial wall would be assumed to lack sterol. 3. what is membrane asymmetry? provide an example? A: i lipid bilayer, the outer and inner halves, have different lipid compositions. (glycolipids for example. More prominent on outer layer, and very sparse on the inner layer) 4.What is homeoviscous adaptation? provide an example A: changes in the composition of membrane temperature to maintain constant fluidity. by changing composition of fatty acids, adjusting amount of sterols (i.e. cholesterols) as a sort if buffering 5. how does the mud shrimp consumption benefit the semi-plamated sandpiper A: fatty acids, are able to enter the muscles more rapidly. 6. distinguish between correlation and causation A:causation, you need to show that the change in one is caused by the change in another. ------ Slide 4 It is the R-groups of the amino acids, that give each amino acid their properties. -1st amino (nonpolar) -2nd (non polar) -3rd (polar and charged) -4th (polar and charged) -5th (non polar) -6th (polar b/c hydroxyl group) -7th (polar, and reactive) -8th (non-polar) Slide 5 -String of amino acids give you structure of protein. -They can later fold depending on the bonding -polypeptide chain, folds into the final composition of the protein. it occurs due to interactions within it. (ionic bonds, disulphide bridge, hydrogen bond) Slide 6 integral membrane proteins: -are embedded in the membrane -extend across entire thickness of membrane -having hydrophilic areas on either side of membrane -hydrofobic trans membrane domains that hold the protein in place within the membrane -transmembrane domains typically 20-0 amino acids long (alpha-helix ) structure -difficult to remove from membrane. held together by hydrophobic interactions Slide 7 Peripheral membrane proteins & Lipid-anchored membrane proteins -both are held on the surface of the membrane -peripheral are held on external or internal. held by non-covalent interactions (hydrophobic, hydrogen bond…) -they are also easy to remove, and have dynamic relationship with membrane -often important as linking proteins, between membrane itself and cytoskeleton lipid anchored protein -held together by covalent interactions with lipids -on cytosolic side you find fatty acid anchored proteins. (covalent bond between protein and fatty acid) -the fatty acid is inserted to membrane by hydrophobic interactions, and this attaches the protein to the membrane it extends out on the surface. (fatty acids always have cytosol
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