Which of the following is an example of an acidic amino acid?

$A$: The polypeptide coil of collagen helix is strengthened by the establishment of hydrogen bonds between the $>NH$ group of the glycine residue of each strand and the $-CO$ group of the other two strands.
$R$: In the collagen helix,a locking effect also occurs with the help of proline and hydroxyproline amino acids.

What type of amino acids are phenylalanine and tyrosine,respectively?

Identify the structures of the amino acids given below.

The primary structure of a protein is determined by which of the following?

$A$: The properties and types of amino acids vary.
$R$: The chemical structure of amino acids differs due to the $R$ group.