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9 September 2019

Viral Multiplication-microbiology|ICDS Supervisor Exam Kerala PSC


Viral Multiplication-microbiology|ICDS Supervisor Exam Kerala PSC

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Viral Multiplication



 Viruses can multiply by two alternative mechanisms: 



the lytic cycle or the lysogenic cycle. 

The lytic cycle ends with the lysis and death of the host cell, whereas the host cell remains alive in the lysogenic cycle. 

The lytic cycle



 The multiplication cycle of these phages, like that of all viruses, occurs in five distinct stages: 

attachment, penetration, biosynthesis, maturation, and release.

 1. Attachment 

After a chance collision between phage particles and bacteria, attachment, or adsorption, occurs. 

During this process, an attachment site on the virus attaches to a complementary receptor site on the bacterial cell. 



The complementary receptor sites are on the bacterial cell wall.


 2. Penetration 


After attachment virus injects its DNA (nucleic acid) into the cell.

 To do this, the bacteriophage’s tail releases an enzyme, phage lysozyme, which breaks down a portion of the bacterial cell wall.

 During the process of penetration, the tail sheath of the phage contracts, and the tail core is driven through the cell wall. 

The capsid remains outside the bacterial cell.

 3. Biosynthesis 


Once  bacteriophage DNA has reached the cytoplasm of the host cell, the biosynthesis of viral nucleic acid and protein occurs. 

Host protein synthesis is stopped by virus induced degradation of the host DNA.Viral RNA/DNA is translated to form 3 types of protein. 



1. Early Protein 2. Intermediate Protein 3. Late Protein 


Early protein shutdown the protein synthesis of host cell it is Immune Depressor Protein. 

Intermediate Protein starts replication of DNA/RNA & start protein synthesis of virus.

Late Protein starts producing the structural protein i.e. Capsid of Virus. 

The host cell’s ribosomes, enzymes, and amino acids are used for translation. 

For several minutes following infection, complete phages cannot be found in the host cell. 


Only separate components— DNA and protein—can be detected.

 The period during viral multiplication when complete, infective virions are not yet present is called the eclipse period

 4. Maturation 

In this process, bacteriophage DNA and capsids are assembled into complete virions.

 The phage heads and tails are separately assembled from protein subunits, and the head is filled with phage DNA and attached to the tail. 


5. Release 

The final stage of viral multiplication is the release of virions from the host cell. 

Lysozyme, enzyme causes the bacterial cell wall to break down, and the newly produced bacteriophages are released from the host cell. 

The released bacteriophages infect other susceptible cells in the vicinity, and the viral multiplication cycle is repeated within those cells.

Viral Multiplication-microbiology|ICDS Supervisor Exam Kerala PSC

Also Read;

Morphology of Bacteria

Anatomy of Bacteria

Vaccination -Types


This topic is important for the ICDS Supervisor Exam.Click  HERE.

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