Name: Multiplication of Viruses
Uploaded: 2019-07-19
Duration: 4 min 22 s
Description: Among viruses, bacteriophages are deadly for bacteria. Bacteriophages are used to combat bacterial diseases. Learn how bacteriophages multiply, in this video.

Question

Explain the lytic cycle with reference to certain viruses.

Accepted Answer

Phages can multiply by two alternative mechanisms: the lytic cycle and the lysogenic cycle. The lytic cycle ends with the lysis or death of the host cell. It is a five-step process involving:

1. Attachment: After a chance of contact between phage particles and bacteria, attachment or adsorption occurs. The phages use tail fibres for attachment to the complementary receptor sites on the bacterial cell wall.

2. Penetration: The tall sheath of the phage contracts and the tail core is driven in through the bacterial cell wall. When the tip of the core reaches the plasma membrane, the DNA from the bacteriophage head passes through the tail core through the plasma membrane and enters the bacterial cell.

3. Biosynthesis: Once the phage DNA reaches the cytoplasm of the host cell, many copies of phage DNA, enzymes and capsid proteins are synthesized, using the cellular machinery of the host cell.

4. Maturation: In this process, bacteriophage DNA and capsids are assembled into complete virions. This period between the infection by a virus and the appearance of the mature virus within the cell is called the eclipse period.

5. Release: The final stage of viral multiplication is the lysis phase of the host cell and the release of virions from the host cell. The plasma membrane of the host cell gets dissolved or lysed due to the viral enzyme, called lysozyme, an enzyme synthesized within the cell and the bacterial cell wall breaks releasing the newly produced phage particles or virions.

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