Question

The idea that a single gene coded for a polypeptide rather than an enzyme was evident from the ______.

Options

• use of X-rays to make nutritional mutants in bread mold.

• transformation of bacteria from rough and non-virulent to smooth and virulent.

• presence of a mutation in one chain of haemoglobin but not in the other.

• discovery that mutated genes changed enzymes in a biochemical pathway.

Answer 1

The idea that a single gene coded for a polypeptide rather than an enzyme was evident from the presence of a mutation in one chain of haemoglobin but not in the other.

Explanation:

The original “one gene-one enzyme” hypothesis, proposed by Beadle and Tatum, suggested that each gene was responsible for producing a specific enzyme. However, scientists realised this was an oversimplification when they studied proteins such as haemoglobin, which is composed of four distinct polypeptide chains (two alpha and two beta). Research showed that a mutation could occur in the genetic code for just one of these chains, such as the beta chain in sickle-cell anaemia, leaving the other chain completely normal. This discovery proved that genes encode individual polypeptides rather than entire complex proteins or enzymes, leading to the more accurate “one gene-one polypeptide” hypothesis.