Question

A collection of mutant strains of Neurospora mold that all require lysine for growth has been found to involve mutations in a number of different genes. Lysine is NOT required in the minimal media for wild-type Neurospora. Explain how mutations in different genes can lead to the same growth requirement.

Answer 1

Lysine is not required in minimal medium by Wild type Neurospora mold is because it can synthesize lysine from alpha ketoglutarate. There are seven enzymes that are involved in this biosynthetic pathway.

The explanation for the mutant strains not able to produce lysine is as per the one gene-one enzyme hypothesis proposed by George Beadle in 1941. The product of one enzymatic reaction is the substrate of the next enzymatic reaction. This applies for the rest of the pathway, where the product of the previous reaction acts as substrate of the next reaction. Thus, if the first enzyme is mutated, then the next enzymatic reaction cannot occur due to no product formation of the previous reaction.

Mutations in any of the enzymes involved in lysine biosynthesis of Neurospora will prevent lysine biosynthesis all reaction after the mutated enzyme catalyzed reaction cannot occur. For lysine to be synthesized, all enzymes in the biosynthetic pathway have therefore to be active. If any one of the enzyme is mutated, the next step also doesn’t take place, further not allowing any subsequent stages. Thus, mutations in several different enzymes will lead to inability to synthesize lysine, causing the mutants to require lysine supplementation in the minimal media.