How would mutations that inactivate each of the following genes affect the determination of the lytic or lysogenic life cycle in mutated λ phage strains? Explain your answers. cI

Verified step by step guidance

1. Understand the role of the cI gene in the λ phage life cycle. The cI gene encodes the λ repressor protein, which is crucial for maintaining the lysogenic state by repressing the lytic genes.
2. Recognize that inactivation of the cI gene would lead to the absence of the λ repressor protein. Without this protein, the repression of lytic genes is lifted.
3. Consider the consequences of the absence of the λ repressor. The lytic genes, which are normally kept inactive in the lysogenic cycle, would become active.
4. Analyze the impact on the life cycle decision. With the lytic genes active, the phage would be more likely to enter the lytic cycle, leading to the production of new phage particles and the eventual lysis of the host cell.
5. Conclude that a mutation inactivating the cI gene would likely shift the balance towards the lytic cycle, as the repression of lytic genes is a key factor in maintaining lysogeny.

Key Concepts

Lytic and Lysogenic Cycles

The lytic and lysogenic cycles are two distinct pathways that bacteriophages, like λ phage, can follow after infecting a host bacterium. In the lytic cycle, the phage replicates rapidly, leading to the destruction of the host cell and the release of new phage particles. In contrast, the lysogenic cycle involves the integration of the phage DNA into the host genome, allowing it to replicate along with the host cell without causing immediate harm.

cI Gene Function

The cI gene in λ phage encodes a repressor protein that is crucial for maintaining the lysogenic state. This protein binds to the operator region of the phage genome, preventing the expression of genes necessary for the lytic cycle. When the cI gene is inactivated by mutations, the repression is lifted, potentially triggering the phage to enter the lytic cycle instead of remaining dormant.

Mutations and Gene Inactivation

Mutations are changes in the DNA sequence that can lead to the inactivation of genes, affecting their normal function. In the context of the cI gene, mutations that disrupt its coding sequence can prevent the synthesis of the repressor protein, thereby altering the balance between the lytic and lysogenic cycles. Understanding how specific mutations impact gene function is essential for predicting the behavior of phage strains in response to genetic changes.