Question
An Immunoglobulin molecule represents the following level of organized protein structure:
A. Primary structure
B. Secondary structure
C. Tertiary structure
D. Quaternary structure
Show Answer
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Correct Answer » D
Explanation
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Ans ‘D’ Quaternary structure
Quaternary Structure
i. Certain polypeptides will aggregate to form one functional protein.This is referred to as the quaternary structure.
ii. The protein will lose its function when the subunits are dissociated.
iii. The forces that keep the quaternary structure are hydrogen bonds, electrostatic bonds, hydrophobic bonds, and van der Waals forces.
iv. Depending on the number of the polypeptide chain, the protein may be termed as the monomer (1 chain), dimer (2 chains), tetramer (4 chains) and so on. Each polypeptide chain is termed as subunit or monomer. Homodimer contains two copies of the same polypeptide chain. Heterodimer contains two different types of polypeptides as a functional unit.
v. For example, 2 alpha-chains and 2 beta-chains forms the Hemoglobin molecule. Similarly, 2heavy chains and 2 light chains form one molecule of immunoglobulin G. Creatine kinase (CK) is a dimer. Lactate dehydrogenase (LDH) is a tetramer.
