Which amino acid contains a secondary amino group in its structure?

The number of essential and non-essential amino acids from the following list respectively is:
Val,Gly,Leu,Lys,Pro,Ser

The $\alpha$-helix structure is found in:

The correct representation of a nucleotide is:

Which of the following is not an essential amino acid?

$\alpha$-$helix$ is a secondary structure of proteins formed by twisting of polypeptide chain into right-handed screw-like structures. Which type of interactions are responsible for making the $\alpha$-$helix$ structure stable?