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. int

Verified step by step guidance

1. Understand the role of the 'int' gene in the λ phage life cycle. The 'int' gene encodes the integrase enzyme, which is crucial for integrating the phage DNA into the host genome, a key step in establishing the lysogenic cycle.
2. Consider the effect of an inactivated 'int' gene. Without a functional integrase enzyme, the phage cannot integrate its DNA into the host genome, which means it cannot enter the lysogenic cycle.
3. Recognize that if the lysogenic cycle is not possible, the phage is more likely to default to the lytic cycle, where it replicates and eventually lyses the host cell.
4. Reflect on the broader implications: the inability to enter the lysogenic cycle could affect the phage's ability to persist in the host population during unfavorable conditions, as the lysogenic cycle allows for dormancy.
5. Summarize that a mutation inactivating the 'int' gene would likely result in a λ phage strain that predominantly follows the lytic cycle, due to the inability to integrate into the host genome and establish 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 bacterial host. 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.

Gene Function in Phage Life Cycles

Specific genes in λ phage are crucial for determining whether the phage enters the lytic or lysogenic cycle. For instance, genes that regulate the expression of proteins involved in the lytic cycle, such as those coding for enzymes that degrade host DNA, or repressors that inhibit the lysogenic pathway, play a significant role in this decision-making process. Mutations that inactivate these genes can shift the balance between these two life cycles.

Mutations and Their Effects

Mutations are changes in the DNA sequence that can alter gene function. In the context of λ phage, mutations that inactivate genes essential for the lytic cycle may lead to a preference for the lysogenic cycle, as the phage may be unable to effectively replicate and lyse the host. Conversely, mutations affecting lysogenic genes could push the phage towards a lytic response, impacting its ability to establish a stable relationship with the host.