What is the number of amino acids present in a single turn of an $\alpha$-helix of a protein?

Discuss the structure and shape of proteins.

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 part of the protein molecule is responsible for the function and activity of the proteins?

In the given pentapeptide, find out an essential amino acid $(Y)$ and the sequence present in the pentapeptide: Choose the correct answer from the options given below:

Explain the classification of proteins based on their molecular structure.