The peptide bond is represented by:

For an amino acid,the ionization constant for the carboxyl group is $pK_{a_1} = 2.34$ and for the ammonium ion is $pK_{a_2} = 9.6$. At what $pH$ will the isoelectric point of the amino acid be?

The compound with the formula $NH_2CH_2COOH$ acts as:

The amino acid containing an indole part is

Which of the following is an amphoteric acid?

Which of the following are sulphur-containing amino acids?

$(A)$. Serine	$(B)$. Cysteine
$(C)$. Lysine	$(D)$. Methionine