What is the correct sequence of events in the lytic cycle of a bacteriophage infection?
A Attachment, Viral DNA penetration into host cell, Integration of viral DNA into host cell DNA, Biosythesis, Maturation, Release
B. Endocytosis of virion, Uncoating, Maturation, and Release
C. Attachment, Fusion of envelope and host cell membrane, Biosynthesis, Maturation, and Release
D. Attachment, Viral DNA penetration, Biosynthesis, Maturation and Release
E. None of the above
The Correct Answer and Explanation is:
The correct answer is:
D. Attachment, Viral DNA penetration, Biosynthesis, Maturation, and Release
Explanation:
The lytic cycle is one of the two major viral replication cycles in bacteriophages (viruses that infect bacteria). It leads to the destruction of the host cell and the release of new viral particles. The sequence of events in the lytic cycle is as follows:
- Attachment (Adsorption):
The bacteriophage attaches to specific receptor sites on the bacterial cell surface. This attachment is highly specific, as it depends on the recognition of receptors on the bacterial surface by proteins on the phage’s tail fibers. - Viral DNA Penetration:
Once the phage is attached, the bacteriophage injects its genetic material (DNA or RNA) into the bacterial cell. The protein coat (capsid) of the virus remains outside the cell. The injection is facilitated by the contraction of the tail sheath in some phages, which acts like a syringe. - Biosynthesis (Replication and Transcription/Translation):
After penetration, the viral genome hijacks the host’s cellular machinery to replicate its DNA and synthesize viral proteins. The host’s own DNA is often degraded to ensure exclusive use of its resources for the production of viral components. - Maturation (Assembly):
During this stage, newly synthesized viral DNA and proteins are assembled into complete, functional virions (new virus particles). This involves packaging the viral genome into newly formed capsids. - Release (Lysis):
Finally, the host cell is lysed (destroyed) by viral enzymes, such as lysozyme, or mechanical rupture. This releases the new phages, which can then infect other bacterial cells, restarting the cycle.
Incorrect Options:
- Option A: Integration of viral DNA into the host genome is part of the lysogenic cycle, not the lytic cycle.
- Option B: Endocytosis and uncoating are typical for animal viruses, not bacteriophages.
- Option C: Fusion of viral envelopes with the host membrane occurs in enveloped animal viruses, not in bacteriophages.