Question

For a protein to have a quaternary structure, it must
A. Consist of two or more polypeptide subunits
B. Consist of four polypeptide subunits
C. Have four domains
D. Exist in several alternative conformational states

Answer 1

Protein is one of the building blocks of body tissue and can also serve as a fuel source. Protein is made up of multiple amino acids that are linked together by peptide bonds, thereby forming a long chain.

Complete step by step answer: The quaternary structure of a protein is the association of several protein chains or subunits into a closely packed arrangement. It consists of more than one amino acid. Each of the subunits has its own primary, secondary, and tertiary structure. The subunits are held together by hydrogen bonds and van der Waals forces between nonpolar side chains.
So, the answer is A, i.e., Consist of two or more polypeptide subunits
Additional information:
The quaternary structure is usually determined by X-ray crystallography. When crystallographic data is difficult or impossible to gather, electron microscopy provides some clues to the quaternary structure. Haemoglobin has a quaternary structure.

Note: The linear sequence of amino acids within a protein is considered the primary structure of the protein. Hydrogen bonding between amino groups and carboxyl groups in neighboring regions of the protein chain sometimes causes certain patterns of folding to occur, which is known as alpha helices and beta sheets. These stable folding patterns make up the secondary structure of a protein. Most proteins contain multiple helices and sheets. The ensemble of formations and folds in a single linear chain of amino acids sometimes called a polypeptide constitutes the tertiary structure of a protein.