Model Answer
0 min readIntroduction
Bacteriophages, literally “bacteria eaters,” are viruses that infect and replicate within bacteria. They are composed of a nucleic acid genome (DNA or RNA) encased in a protein coat called a capsid. Bacteriophages employ two primary reproductive cycles: the lytic cycle and the lysogenic cycle. The lytic cycle results in the destruction of the host bacterial cell, releasing new phage particles. Understanding this cycle is crucial in fields like microbiology, genetic engineering, and phage therapy, offering potential alternatives to antibiotics in combating bacterial infections.
The Lytic Cycle of Bacteriophages: A Step-by-Step Explanation
The lytic cycle is a five-stage process that culminates in the lysis (rupture) of the host bacterial cell. Each stage is critical for successful phage replication.
1. Attachment (Adsorption)
The lytic cycle begins with the attachment of the phage to specific receptor sites on the bacterial cell surface. This interaction is highly specific; a phage can only infect bacteria possessing compatible receptors. These receptors can be proteins, carbohydrates, or lipopolysaccharides present on the bacterial cell wall.
2. Penetration (Entry)
Following attachment, the phage injects its genetic material (DNA or RNA) into the bacterial cytoplasm. The capsid remains outside the cell. This penetration can occur through various mechanisms, including direct injection through the cell wall or utilizing bacterial transport systems.
3. Biosynthesis (Replication & Synthesis)
Once inside the host cell, the phage genome takes control of the bacterial machinery. The phage DNA directs the synthesis of new phage components – nucleic acids (DNA or RNA), capsid proteins, and enzymes necessary for assembly. The bacterial cell’s resources are diverted from its own metabolic processes to produce these phage components. This stage involves the replication of the phage genome and the transcription and translation of phage genes.
4. Maturation (Assembly)
The newly synthesized phage components are assembled into complete phage particles (virions). Capsid proteins self-assemble around the replicated phage genome. This is a complex process requiring specific enzymes and molecular chaperones. The assembled virions are structurally complete and ready to infect new host cells.
5. Lysis (Release)
The final stage involves the lysis of the bacterial cell wall. The phage produces enzymes, such as lysozyme, that break down the bacterial cell wall, causing it to rupture. This releases the newly formed phage particles into the surrounding environment, allowing them to infect other susceptible bacteria. This process effectively terminates the host cell’s life.
The entire lytic cycle can be remarkably rapid, often completed within 20-30 minutes, depending on the phage and the host bacterium. This rapid replication rate contributes to the effectiveness of bacteriophages as agents of bacterial control.
Conclusion
The lytic cycle is a fundamental process in bacteriophage biology, demonstrating a highly efficient mechanism for viral replication and bacterial destruction. Its understanding is vital not only for comprehending microbial interactions but also for exploring potential applications in areas like phage therapy, offering a promising avenue to combat antibiotic resistance. Further research into phage biology and the lytic cycle will undoubtedly unlock new strategies for controlling bacterial infections and manipulating microbial communities.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.