Question

Protomers are
A. Primitive proteins
B. Protein subunits
C. Protein aggregates
D. None of the above

Answer 1

Hint:- Proteins are linear polymers of amino acids. Their structure contains one or more polypeptide chains. These essential macromolecules take part in the maintenance and metabolic processes of living cells.

Complete step-by-step solution:- Many proteins often exist in aggregated states. The total molecular weight of such proteins is greater than 50,000 daltons. The assembly of multiple polypeptide chains results in the formation of a quaternary structure.
Proteins formed by a single polypeptide chain are called Monomeric proteins, e.g., lysozyme, myoglobin. Whereas, those having 2 or more polypeptide chains are called Oligomeric proteins. Oligomeric proteins may have many identical repeating units of monomers or different repeating units of monomers. Each of these repeating units of monomer is called a subunit or protomer. To indicate whether the subunits are similar or different, prefixes homo and hetero are used respectively. For example,
Lactose repressor protein consists of four identical subunits and so it is referred to as a homotetramer.
Hemoglobin is a tetramer having two α-protometers and two β- protomers, so it is referred to as a heterotetramer.
So, the correct answer is (B), Protein subunits.
Additional information:
In large proteins, protomers or subunits are held together with the help of hydrophobic forces. These forces become weak at low temperatures due to which many subunit proteins may fall apart at low temperatures.
Capsomeres of viruses contain multiple protein subunits.

Note:- The protomers in a protein are usually found in even numbers. Protein structures having two, three, four, multiple subunits are called dimer, trimer, tetramer, oligomer or multimer respectively. Rarely a multimeric protein has an odd number of subunits.