Question

Differentiate between lytic and lysogenic cycles.

Short answer

The lytic cycle destroys the host cell while immediately producing new viruses, whereas the lysogenic cycle integrates viral DNA into the host genome and does not destroy the cell.

Step-by-step solution

Definition of Lytic Cycle

In the lytic cycle, a virus infects a host cell, takes over the cell's machinery to replicate its own genetic material, and then causes the cell to burst (lyse), releasing new virus particles.

Lytic Cycle Phases

The lytic cycle consists of the following phases:1. Attachment: The virus binds to the surface of the host cell.2. Penetration: The virus injects its genetic material into the host cell.3. Biosynthesis: The virus's genetic material takes control of the host cell's machinery to create viral components.4. Maturation: New viral particles are assembled inside the host cell.5. Lysis: The host cell bursts, releasing new viruses.

Definition of Lysogenic Cycle

In the lysogenic cycle, the viral DNA integrates into the host cell's genome, where it can remain dormant for a long period. When the host cell replicates, it also replicates the viral DNA.

Lysogenic Cycle Phases

The lysogenic cycle consists of the following phases:1. Attachment: The virus binds to the surface of the host cell.2. Penetration: The virus injects its genetic material into the host cell.3. Integration: The viral DNA incorporates into the host cell's genome and becomes a prophage.4. Replication: The host cell replicates its own DNA along with the integrated viral DNA, often without harming the host cell.

Key Differences

The key differences between the lytic and lysogenic cycles are:1. Outcome for Host Cell: The lytic cycle results in the destruction of the host cell, whereas the lysogenic cycle does not.2. Viral DNA Integration: In the lysogenic cycle, viral DNA integrates into the host cell's genome; in contrast, in the lytic cycle, it does not.3. Duration: The lysogenic cycle can have a prolonged dormant phase, whereas the lytic cycle is shorter and immediately results in new virus production.

Key concepts

virus replication

Virus replication is the process by which viruses produce new copies of themselves using the machinery of a host cell. Viruses are not able to replicate independently; instead, they rely on infecting a host cell and hijacking its cellular processes.

There are two main cycles through which viruses replicate: the lytic cycle and the lysogenic cycle. Understanding these cycles is key to understanding how different viruses spread and cause disease.

host cell

A host cell is the cell that a virus infects. Viruses must attack and enter a host cell because they need the host's resources to replicate.

The virus attaches to the host cell's surface and injects its genetic material into it. In the case of the lytic cycle, the virus quickly starts to produce new virus particles. During the lysogenic cycle, however, the viral DNA integrates into the host cell's genome and can remain inactive for some time.

viral DNA integration

Viral DNA integration is a key feature of the lysogenic cycle. Once the virus injects its genetic material into the host cell, the viral DNA is incorporated into the host cell's genome. This integrated viral DNA, called a prophage, can lay dormant.

During this dormant phase, the viral DNA is replicated along with the host cell's DNA whenever the host cell divides. This means that all new cells will also carry the viral DNA. This integration does not immediately harm the host cell but can reactivate under certain conditions to enter the lytic cycle.

lysis

Lysis is the final phase of the lytic cycle. In this phase, the host cell bursts, or lyses, releasing new virus particles into the surroundings. The bursting of the cell is caused by the accumulation of new virus particles inside the cell, which eventually causes the cell membrane to rupture.

This destruction of the host cell results in the release of new viruses that can go on to infect other cells. The lytic cycle, therefore, leads to the quick spread of the virus and immediate consequences for the infected organism.

prophage

A prophage is the viral DNA that has been integrated into the host cell's genome during the lysogenic cycle. This integration allows the viral DNA to be replicated along with the host cell's DNA without causing immediate harm.

The prophage can remain dormant for long periods, allowing it to be passed on to successive generations of cells. Under certain conditions, the prophage can be activated and enter the lytic cycle, leading to the production of new virus particles and the eventual destruction of the host cell.