Question

Explain step 1 involved in both the lytic and lysogenic cycles of a bacteriophage.

Answer 1

Bacteriophages can replicate through both the lytic cycle, which destroys the host cell, and the lysogenic cycle, where phage DNA is integrated into the host's genome. The lytic cycle includes attachment, penetration, biosynthesis, maturation, and release. In contrast, the lysogenic cycle involves integration of the phage DNA into the host genome, replication with the host cell, and potential induction back into the lytic cycle under stress.

Step-by-step explanation:

Bacteriophages can undergo two types of replication cycles: the lytic cycle and the lysogenic cycle. During the lytic cycle, the phage replicates and eventually causes lysis (destruction) of the host cell. In contrast, the lysogenic cycle involves integration of phage DNA into the host genome, where it can be replicated along with the cell's own DNA and transmitted to new cells when the host cell divides.

Lytic Cycle

In the lytic cycle, there are several key steps:

1. Attachment: The phage binds to specific receptors on the bacterial cell surface.
2. Penetration: The phage injects its DNA into the host cell.
3. Biosynthesis: The phage commandeers host cell machinery to produce viral components.
4. Maturation: New phage particles are assembled inside the cell.
5. Release: The cell is lysed, releasing new phages.

Lysogenic Cycle

In the lysogenic cycle:

1. The phage DNA integrates into the bacterial genome, forming a prophage.
2. The prophage DNA is replicated along with the host genome during cell division.
3. Environmental stressors may trigger the excision of the prophage DNA, causing the phage to revert to the lytic cycle.

Viruses like the T4 phage demonstrate the lytic cycle, while the λ (lambda) phage is an example of a bacteriophage that can undergo the lysogenic cycle.