What type of substance is an amino acid?

In protein synthesis,the first amino acid is known as $.....P.....$ and the last amino acid is known as $.....Q.....$.

Cysteine and methionine are amino acids containing $........$.

Match the following Column-$I$ with Column-$II$ and select the correct option.

Column-$I$ (Type of Amino Acid)	Column-$II$ (Example)
$(A)$ Polar and uncharged $R$ group	$(i)$ Methionine
$(B)$ Non-polar $R$ group	$(ii)$ Glutamic acid
$(C)$ Polar and negatively charged $R$ group	$(iii)$ Lysine
$(D)$ Polar and positively charged $R$ group	$(iv)$ Cysteine

Which of the following molecules is amphoteric in nature?

At which level of organization does a protein consisting of only a single polypeptide become functional?