Which of the following amino acids contains sulfur?

An electric current is passed through an aqueous solution of a mixture of alanine (isoelectric point $6.0$), glutamic acid $(3.2)$, and arginine $(10.7)$ buffered at $pH$ $6.0$. What is the fate of the three amino acids?

Which among the following is a globular protein?

The artificial sweetener aspartame $(A)$,$H_3N^{+}-CH(CH_2COO^{-})-CONH-CH(CH_2Ph)-COOCH_3$,is converted to . . . . . . on storage for extended periods of time in aqueous solution:

$A$ tetrapeptide $x$ on complete hydrolysis produced glycine $(Gly)$,alanine $(Ala)$,valine $(Val)$,and leucine $(Leu)$ in equimolar proportions. The number of possible tetrapeptide sequences involving each of these amino acids exactly once is:

At the isoelectric point,in which form does an amino acid exist?