When proteins are heated with concentrated $HNO_3$,a yellow color is obtained. What is this test called?

The number of cyclic tripeptides formed with $2$ amino acids $A$ and $B$ is:

The trace metal present in insulin is

The secondary structure of protein is stabilized by:

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 of the following is not a classification of proteins?