BCH 361 Lecture Notes - Lecture 3: Substance P, Lysine, Amphoterism
5 Feb 2017
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The carboxyl and amino groups can act as an acid or base. Molecules that can be a base or an acid simultaneously= amphoteric. At physiological ph (7. 2), the carboxyl group donates h+ while the amino group accepts a h+ At ph 7. 2 amino acids are dipolar ions = zwitterions. Despite charges, at ph 7. 2, these amino acids are neutral (but the r group will matter) Pka is a measure of the tendency of a group to give up a proton- as pka increases by 1 unit, the tendency decreases tenfold. At acidic ph, the carboxyl group is protonated and the amino acid is in the cationic form. At neutral ph, the carboxyl group is deprotonated but the amino group is protonated. The net charge is zero; such ions are called zwitterions. At alkaline ph, the amino group is neutral nh2 and the amino acid is in the anionic form. Oxytocin (think childbirth) sex-peptide (think fruit fly mating)
