Lecture 2

1 h ydropathy s cale for amino acid residues four

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Unformatted text preview: 3N C H3C +H H 3N C CH2 CH CH3 Alanine Ala A COO- COO- COO- COO+H CH3 Valine Val V CH H2C CH H3C H CH3 Hydropathy: the relative h ydrophobicity of each amino acid, measured in the free-energy change for the transfer of an amino acid from a hydrophobic solvent to water. Large positive means more hydrophobic. CH3 CH3 Leucine Leu L apolar solvent Isoeucine Ile I ΔG = -RT ln K eq Keq = The structures of micelles and soluble proteins are due to the hydrophobic effect. Aliphatic/Structural • Proline (Pro, P) - has a pyrrolidine ring and restricts the geometry of polypeptides [Aqueous] [Apolar] water Amino acid Free-energy change for transfer (kjmol-1) Highly hydrophobic Isoleucine Phenylalanine Valine Leucine Methionine Less hydrophobic Tryptophan Alanine Glycine Cysteine Tyrosine Proline Threonine Serine Highly hydrophilic Histidine Glutamate -2.6 Asparagine Glutamine -2.9 Apartate Lysine Arginine 3.1 2.5 2.3 2.2 1.1 1.5* 1.0 0 .67 0.17 0.08 -0.29 -0.75 -1.1 -1.7 -2.7 -3.0 -4.6 -7.5 Aromatic amino acid structures • Glycine (Gly,G) - has a hydrogen for the R-group. The C α is not chiral. Page 58 COO+H 3N C H H Gly...
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