BCHE 395-4 2014 Amino Acids

3 4 opqcally acqve isomers levo lej equal mixture

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Unformatted text preview: n Amino acid behavior reflects zwieerion property Amino Acids •  •  •  •  α carbon is tetrahedral Binds four groups α carbon is chiral (except glycine; R = H) Two nonsuperimposable stereoisomers or enanNomers can exist Amino Acids •  Called L- and D- isomers •  Pure soluQons can bend polarized light in opposite direcQons •  L- and D- isomers are mirrored images •  L- isomer only used biologically to build proteins (L = Life) •  Based on glyceraldehyde: L has H group on the right- hand side of chiral carbon, poinQng “up” (L fig. 3- 4) OpQcally acQve isomers Levo (lej) Equal mixture of both = racemic Dextro- right PerspecQve formula ProjecQon formula Features of the 20 Natural (common) L- Amino Acids •  ClassificaNons: 5 groups •  Nonpolar, aliphaQc (non- aromaQc) hydrophobic R groups (7) •  Polar, uncharged R groups (5) •  AromaQc R groups (3) •  PosiQvely charged R groups (3) •  NegaQvely charged R groups (2) FuncQonality of R Groups •  In case you haven’t guessed, R groups are important! •  And there are LOTS of ways to group them! •  Unique R groups determine chemical and biological reacNvity, for example: •  - Polar and charged R groups à༎ hydrophilic •  - Nonpolar, aliphaQc R groups à༎ hydrophobic •  - Can have direct bearing on locaQon within a protein structure Be able to identify the R –  i.e. Facing water or Buried inside functional groups and their chemical, physical characteristics! How would you label the non- α carbons? Labeling ConvenQon- Carbons! •  Organic nomenclature: start from one end •  Biochemical designaQon: –  start from α- carbon and go down the R- group PosiQve R Groups...
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