Structures of alanine at $pH = 2$ and $pH = 10$ are respectively

The number of peptide bonds in the compound is:

The total number of distinct naturally occurring amino acids obtained by complete acidic hydrolysis of the peptide shown below is

What is the monomer of a polypeptide?

$A$ protein undergoes reversible thermal denaturation from its initial state $N$ to denatured state $D$ according to $N \rightleftharpoons D$. At $60 ^\circ C$, the concentrations of both $N$ and $D$ are equal at equilibrium, and the standard enthalpy change of denaturation is $666 \text{ kJ mol}^{-1}$. The standard entropy change ($\Delta S^\circ$ in $\text{kJ K}^{-1} \text{mol}^{-1}$) of the protein upon denaturation at $60 ^\circ C$ is closest to

Which one of the following is an essential amino acid?