In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of consensus sequence in the lac promoter

Verified step by step guidance

1. Identify the role of the lac promoter in the lac operon, which is to initiate transcription of the operon genes.
2. Understand that the consensus sequence in the promoter is crucial for the binding of RNA polymerase, which is necessary for transcription initiation.
3. Consider the effect of a mutation in the consensus sequence: it may reduce or prevent RNA polymerase binding, leading to decreased or abolished transcription of the operon genes.
4. Recognize that the severity of the effect depends on the nature of the mutation: a minor change might only slightly reduce transcription, while a major alteration could completely inhibit it.
5. Conclude that a mutation in the consensus sequence of the lac promoter is likely to result in reduced or no transcription of the lac operon genes, affecting the operon's ability to respond to lactose presence.

Key Concepts

Lac Operon

The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It consists of three structural genes (lacZ, lacY, and lacA) and is regulated by a promoter and an operator. The operon is activated in the presence of lactose and repressed when glucose is available, demonstrating a classic example of gene regulation in prokaryotes.

Promoter Consensus Sequence

A promoter consensus sequence is a short, conserved sequence of DNA that is recognized by RNA polymerase and transcription factors to initiate transcription. In the lac operon, mutations in this sequence can significantly affect the binding efficiency of RNA polymerase, leading to altered levels of gene expression. This can result in either reduced or enhanced transcription of the operon genes.

Transcription Regulation

Transcription regulation refers to the mechanisms that control the rate of gene transcription, ensuring that genes are expressed at the right time and in the right amounts. In the context of the lac operon, mutations affecting the promoter can disrupt the normal regulatory processes, leading to either constitutive expression (always on) or complete silencing of the operon, depending on the nature of the mutation.