$1.$ Glycylglycine
$2.$ Alanylalanine
$3.$ Glycylalanine
$4.$ Alanylglycine
The dipeptides which may be obtained from the amino acids glycine and alanine are

The secondary structure of a protein refers to

Which one of the following is an amino acid?

$A$ protein '$X$' with a molecular weight of $70,000 \ u$,on hydrolysis gives amino acids. One of these amino acids is:

In the following compound,the favourable site/s for protonation is/are:
(Image description: Adenine structure with labels $a$ on the exocyclic $-NH_2$ group,$b$ on the pyrimidine ring nitrogen,$c$ on the other pyrimidine ring nitrogen,$d$ on the imidazole ring nitrogen,and $e$ on the imidazole ring $-NH-$ group.)

Stability of $\alpha$-Helix structure of proteins depends upon: