Quaternary structure is present in

The correct option is D Haemoglobin
$\text{Introduction to proteins}$

Proteins can be defined as the polymers of amino acids linked to each other through the peptide bonds.

There are four levels of structural organisation found in proteins. These are:

• Primary structure (one dimensional structure)
• Secondary structure (alpha helix and beta sheet)
• Tertiary structure - Three dimensional structure of protein
• Quaternary structure

$\text{Quaternary structure}$

Quaternary protein structure is made up of two or more polypeptide chains that are held together by noncovalent interactions like hydrogen bonds, hydrophobic interactions, ionic bonds, etc.

$\text{Haemoglobin}$

Haemoglobin is a quaternary tetrameric protein which consists of four units of two different protein chains, $\alpha$ and $\beta .$

This protein is present in the RBCs and is responsible for the transport of oxygen to the cells and tissues of the body.

$\text{Final answer}$

(b) Haemoglobin