Pepsin enzyme hydrolyses:

Identify the essential amino acids from the following:
$A$) Leucine
$B$) Tyrosine
$C$) Cysteine
$D$) Histidine

Which of the following compounds exists as a zwitterion?

If there are $20$ naturally occurring amino acids,what is the maximum number of tripeptides that can be formed?

Which characteristic of $Proline$ (an amino acid) distinguishes it from other naturally occurring amino acids?

Assertion $(A)$: An optically active amino acid can exist in three forms depending on the $pH$ of the solution.
Reason $(R)$: Amino acids contain both acidic and basic groups; they exist as a zwitterion in aqueous medium,anionic form in basic medium,and cationic form in acidic medium.