lecture3 - Amino acid: a compound that contains Amino Amino...

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Amino Acids Amino Acids Amino acid: Amino acid: a compound that contains both an amino group and a carboxyl group Basic building blocks for proteins α α -Amino acid -Amino acid : a structure in which the amino group is on the carbon adjacent to the carboxyl group α -amino acids are written in the zwitterion zwitterion (internal salt) form (no net charge) H O R C C O NH3 + side chain α carbon
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Chirality of Amino Acids Chirality of Amino Acids With the exception of glycine, all amino acids found in proteins have at least one stereocenter (the α -carbon) and are chiral all amino acids found in proteins have the L- configuration at the α -carbon H NH 3 + COO - CH 3 + H 3 N H COO - CH 3 D-Alanine L-Alanine (Fischer projections)
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Chirality of Amino Acids Chirality of Amino Acids Chirality is determined based on comparison to glyceraldehyde (Fischer projection formulas) H NH 3 + COO - CH 3 + H 3 N H COO - CH 3 D-Alanine L-Alanine H OH CHO CH 2 OH HO H CHO CH 2 OH D-Glyceraldehyde L-Glyceraldehyde the naturally  occurring form the naturally  occurring form
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Non-polar amino acids Non-polar amino acids Nonpolar side chains  (predominant form at pH 7.0) H- CH 3 - CH 3 CH 2 CH( CH 3 ) - ( CH 3 ) 2 CHCH 2 - CH 3 SCH 2 CH 2 - N H ( CH 3 ) 2 CH glycine (gly, G) alanine (ala, A) valine (val, V) leucine (leu, L) isoleucine (ile, I) methionine (met, M) phenylalanine (phe, F) tryptophan (trp, W) N H H + proline (Pro, P)
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Features of Non polar AAs Features of Non polar AAs - alanine, valine, leucine, and isoleucine have aliphatic side chains - methionine has an aliphatic side chain with a sulfur atom - this is the first aa for most proteins - proline has a second amino group- makes it an imine - has cyclic structure: very rigid AA - phenylalanine and tryptophan have aromatic side chains - isoleucine has a second stereocenter
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Polar amino acids Polar amino acids Polar side chains  (predominant form at pH 7.0) asparagine (asn, N) glutamine (glu, G) serine (ser, S) threonine (thr, T) H 2 NCCH 2 - O H 2 NCCH 2 CH 2 - O HOCH 2 - CH 3 CH- OH tyrosine (tyr, Y) HO C H 2 - Q Acidic side chains  (predominant form at pH 7.0) aspartic acid (asp, D) glutamic acid (glu, E) cysteine (cys, C) -O C H 2 -H SC 2C
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Features of Polar AAs - serine and threonine have a hydroxyl group bonded to the aliphatic side chain - tyrosine has a -OH bonded to an aromatic side chain - Serine, threonine, and tyrosine can be phosphorylated to regulate protein activity - cysteine has a thiol group (-SH) as part of the aliphatic
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This document was uploaded on 01/28/2011.

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lecture3 - Amino acid: a compound that contains Amino Amino...

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