amino_acids

amino_acids - Chemistry 237 Amino Acids Amino Acids general...

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Chemistry 237 Amino Acids
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general formula structures and properties titration curves optical activity non-standard amino acids Reactions involving amino acids Amino Acids
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The 20 protein amino acids are called α -amino acids neutral form of an α-amino acid zwitterionic form of an α-amino acid Why α-amino acids ? Because the NH 3 group is on the alpha carbon. The carbon next to a carbonyl group is called the alpha (α)-carbon, then the β- carbon, γ-carbon, etc. O O- a b
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Amino acids Amino acids can act as an acid or a base. The have at least 2 ionizable groups. -COOH H 2 N-
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Classifying the Amino Acids NON-POLAR Small side chain: Gly, Ala Branched-chain: Val, Ile, Leu Aromatic side chains: Phe, Trp (Tyr) POLAR Uncharged polar side chains: Ser, Thr, Tyr, Gln, Asn Charged polar side chains: Lys, Arg, His (positive charge) Asp, Glu (negative charge)
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These are called the hydrophobic side chains. In aqueous solution the hydrophobic effect will cause these residues to cluster or aggregate in the protein interior. In addition to the hydrophobic effect, London dispersion forces are the primary interactions between the side chains in a folded protein.
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Classifying the Amino Acids NON-POLAR Small side chain: Gly, Ala Branched-chain: Val, Ile, Leu Aromatic side chains: Phe, Trp (Tyr) POLAR Uncharged polar side chains: Ser, Thr, Tyr, Gln, Asn Charged polar side chains: Lys, Arg, His (positive charge) Asp, Glu (negative charge)
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These side chains are the polar uncharged side chains. They can hydrogen bond to each other and in some case to the backbone group Some texts say that SH in cys cannot H bond but H bonds to cysteine have been observed in several crystal structures of proteins These are the charged amino acids. Each side chain has an ionizable group. Ionic interactions between oppositely charged side chains stabilize the folded structures of proteins. Histidine is extrememly important because the pKa is close to 7
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Alphabetical list of the 20 amino acids You are expected to know the structures of the 20 protein amino acids The single letter amino acid code is not necessary but is VERY USEFUL!
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Acideroids http://www.wiley.com/legacy/college/boyer /0470003790/animations/acideroids/acider oids.htm • Caution: This game will teach you to recognize the 20 common amino acids. You must also be able to draw them, and know the pKa and three letter codes.
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One other variant: cystine (disulfide of Cys): Cystine oxidation
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Silly stuff on the web http://moltoys.blogspot.com/ amino acid beads http://faculty.washington.edu/crowther/Misc/Songs/alanin e.shtml an amino acid poem
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Acid-Base Properties Amino acids are polyprotic weak acids.
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amino_acids - Chemistry 237 Amino Acids Amino Acids general...

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