Insulin is

Enzymes belong to which class of compounds?

Treatment of compound $O$ ($1,2-$diethylbenzene) with $KMnO_4 / H^{+}$ gives $P$ (phthalic acid),which on heating with ammonia gives $Q$ (phthalamide). The compound $Q$ on treatment with $Br_2 / NaOH$ produces $R$ ($o-$phenylenediamine). On strong heating,$Q$ gives $S$ (phthalimide),which on further treatment with ethyl $2-$bromopropanoate in the presence of $KOH$ followed by acidification,gives a compound $T$.
$(1)$ The compound $R$ is
$(2)$ The compound $T$ is
$(A)$ glycine
$(B)$ alanine
$(C)$ valine
$(D)$ serine
Identify the correct options for $(1)$ and $(2)$.

$\alpha$-Amino acids are:

The most important energy source in every living cell is $......$.

Amino acids can be classified as $\alpha$,$\beta$,$\gamma$,$\delta$ and so on,depending upon the relative positions of the amino group with respect to the carboxyl group. Which type of amino acids form polypeptide chains in proteins?