George Beadle and Edward Tatum used mutant strains of Neurospora to formulate the one-gene-one-enzyme hypothesis. Researchers later updated this hypothesis to propose that one gene encodes one polypeptide because proteins can have multiple subunits. Consider a heterodimeric protein. How many genes are required to form this protein?

(A) two

(B) four

(C) six

(D) three

(E) one

(A) two

Explanation:

A heterodimeric protein consists of two polypeptides (a polypeptide is a chain of amino acids) that differ in amino acid composition, number or order in the chain sequence. Each polypeptide makes a different subunit of the protein.

One gene encodes one polypeptide, so if the protein has two different polypeptides, two genes are required to form this protein.