CHM361H5 Lecture Notes - Lecture 6: Tautomer, Acid Dissociation Constant, Stage Name
Document Summary
Side group with a poisitive charge at physiological ph (ph ~7) Exists as a tautomer at ph 7 because pka is 6. R group has a negative charge at physiological ph ~7. Pka ~ 4 > pka of cooh. Pka ~ 4. 3 > pka of cooh. The basic and acidic amino acids can be involved in protein-protein, protein-dna interaction, folding. Amino acids are weak polyprotic acids; degree of ionization depends on the ph. Only backbone amino and carboxyl groups are titrable. This is also true for valine, alanine, glutamine, asparagine, isoleucine, Gly+ + h20 glyo + h3o+ The amino group makes it more acidic. The amino group (nh3+) is an electron withdrawing group and so balances the negative charge on the coo- and stabilizes the charge. Gly0 + h20 gly-1 + h3o+ This is lower than the pka of lys r group (nh3+) Will be fully protonated and uncharged at ph 7.
