Which of the following amino acids contains a polar and uncharged $R$-group?

The structure of hemoglobin contains ......... heme groups.

The helical structure of protein is stabilized by

$A$: 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.

Which of the following macromolecules is found in the structure of hormones and enzymes?

Which elements are present in the structure of proteins?