Polypeptide chains present in insulin are linked together by:

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

Which of the following statements correctly describe the functions of proteins?
$(I)$ As an enzyme
$(II)$ As a hormone
$(III)$ Fight against infectious organisms
$(IV)$ Formation of genetic material

$S$ - Statement: Hemoglobin is a conjugated protein.
$R$ - Reason: Hemoglobin contains globin protein in its structure.

Collagen is

The peptide chains loop,twist and fold back on themselves due to the formation of . . . . . . bonds to form a stable tertiary structure of protein.