The water-soluble protein is:

Which of the following statements are correct? A) $\alpha - \text{amino acids present in protein is L- amino acid.}$ B) $\text{Amino acids contain } NH_2 \text{ as well as COOH group.}$ C) $\text{Number of amino group and carboxylic group are same in amino acids always.}$ D) $\text{Tryosine was firstly obtained from cheese.}$ Choose the correct alternatives from below:

Which $\alpha$-amino acid can cross-link peptide chains?

Which amino acid from the following is $NOT$ synthesized in our body?

Which from the following is $NOT$ a globular protein?

$\alpha$-$helix$ 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?