amino acids met dank aan dr. detke. most amino acids are chiral all naturally occuring amino acids...
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Amino acids
Met dank aan Dr. Detke
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Most amino acids are chiral All naturally occuring amino acids
except Gly are the L isomer L & D amino acids are stereoisomers
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Most amino acids are zwitterions amino acids
are zwitterions at neutral pH (contains negative and positive charged groups)
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Small aliphatic amino acids Glycine
non-chiral smallest most flexible in
polypeptides less hydrophobic
Alanine chiral next smallest less hydrophobic
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Other aliphatic amino acids
Val, Leu, Ile Highly hydrophobic branched side-chains
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Yet another aliphatic amino acid
Proline imino acid rigid ring structure puts kinks in
polypeptides
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Aromatic amino acidsPhenylalanine•Absorbs UV•Very hydrophobic
Tyrosine•Absorbs UV•less hydrophobic•H-bonds•OH can ionize•OH can be modified
Tryptophan•Really absorbs UV!•less hydrophobic•H-bonds
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Sulfur-containing amino acids
Methionine highly hydrophobic initiator amino acid
Cysteine less hydrophobic forms disulfide bonds SH group can ionize
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Oxidation of cysteine to cystine
Disulfide bond formation is reversible
Disulfide bonds form in proteins and help stabilize their structures
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Alcoholic amino acids
Ser, Thr less hydrophobic H-bonding potential can be modified Thr is an isostere of
Val
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Acidic amino acids
Asp, Glu highly
hydrophilic negatively
charged at neutral pH
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Basic amino acids Highly hydrophilic Lys and Arg are positively charged at neutral pH His is partially charged at neutral pH
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Amide-containing amino acids
Asn, Gln highly hydrophilic H-bonding potential isosteres of Asp and
Glu
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Peptide bond formation
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The peptide bond is planar
Fig. 4.6
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Aspartame – a dipeptide
200X Sweeter than Sucrose !!!
aspartylphenylalanine methyl ester