Question

The pI value for amino acid cysteine is 5.1. Draw the structure of cysteine that predominates in a solution at each of the following pH values:
a. pH < 1
b. pH = 5.1
c. pH > 12

Answer 1

Answer on Question #52888 – Biology – Biochemistry

Under pH < 1 additional hydrogen ion is attached to amino group, leading to partially positive charge:

Under pH 5.1 amino acid is under the isoelectric point when the net charge is 0 and amino acids is in the form of zwitter ion:

Under pH >12, both carboxyl and sulfhydryl groups are ionized, leading to partially negative charge:

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