Classical Sociological Theory
Classical Sociological Theory SOCA 100
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80204 - BIOL 2220 - 002
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This 2 page Class Notes was uploaded by Francesca Rath on Thursday October 22, 2015. The Class Notes belongs to SOCA 100 at University of California - San Diego taught by Staff in Fall. Since its upload, it has received 21 views. For similar materials see /class/226810/soca-100-university-of-california-san-diego in Sociology at University of California - San Diego.
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Date Created: 10/22/15
mikedaVis45hotmailcom Week 3 Handout Section A04 Tuesday 5550 WLH 2207 TERTIARY STRUCTURE DOMAINS Tertiary Structure Tertiary structure concerns interactions between amino acids located more distantly in the polypeptide chain Domains or tertiary structure arise when secondary structures such as alpha helices come together to form a higher order functional unit A single polypeptide can fold into one or multiple domains Alpha Domains 7 Alpha domains are formed by alpha helices and loops packing together to make a stable globular structure through helixhelix interactions 7C0iled coils are a pair of righthanded alpha helices wrapped around each other to form a lefthanded superhelix Coiled coils are the basis for alpha domains Coiledcoils interact according to the knobsinholes model where the side chains of one alpha helix insert between the side chains of another Coiling reduces the number of residuestum from 36 to 35 so that the patter of side chain interactions repeats after 2 turns 7 residues This is known as the heptad repeat The heptad repeat with amino acids labeled ag has certain requirements i usually leucine or isoleucine in d position ii hydrophobic in a position iii charged residues in e amp g positions 1 Fourhelical bundle g 3637 7 This is the simplest and most frequent alpha helical domain consisting of 4 alpha helices usually two coiledcoils arranged in a bundle to form a hydrophobic core 7 Side chains in bundles interact by the ridgesingrooves model by which side chains extending from the surface of the helix form raised rows separated by shallow grooves The ridges of one amino acid settle in the grooves of a second 7 One example of a fourhelical bundle is found in human growth hormone What is special about its conformation 2 Globin fold g 310 7 The globin fold is constructed from eight alpha helices AH of variable lengths connected by loops in such a way that it creates an active site in which a prosthetic group eg iron can bind 7 Examples hemoglobin myoglobin AlphaBeta Domains N W 7 AlphaBeta domains are the most commonly observed domain structure In general they consist of parallel or mixed beta sheets connected and surrounded by alpha helices Alphabeta barrels fig 4 l578 7 Alphabeta barrels must have at least 8 parallel beta strands can be more that form a closed circle and enclose a hydrophobic core Cross connections between the parallel beta strands are alpha helices as in the betaalphabeta motif All alpha helices are on one side of the beta sheet 7 The active site of all alphabeta barrels is found in a pocket formed when carboxy ends of parallel strands loop to connect to amino ends of adjacent alpha helices see g 48 Horseshoefold fig 4 l l 7 The horseshoe fold is a leucinerich domain formed by repeats of betaloop alpha domains such as in alphabeta barrels with all the alpha helices on one side of the parallel betasheet However instead of forming a closed barrel they form a curved open structure which resembles a horseshoe 7 One side of the beta sheet faces the alpha helices and forms a hydrophobic core between the helices and the betasheet The other side of the betasheet is exposed to the solvent Which side should the leucine residues be facing Open twisted sheets fig 41321 7 Open twisted sheets have alphahelices on both sides of the sheet 7 Examples avodoxin Adenyl Kinase 7 Active sites are formed at topological switchpoints These occur in crevices formed when there are 2 adjacent connections that are on opposite sides of the beta sheet In the topology diagram this occurs at the place where connections from the carboxy ends of 2 adjacent beta strands go in opposite directions you should be able to look at the schematic diagram of a twisted sheet and be able to draw the topological diagram and identify the locations of crevices active sites
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