Viruses and Their Replication - Attachment and Entry of Bacteriophage T4

9 important questions on Viruses and Their Replication - Attachment and Entry of Bacteriophage T4

What determines the host range of a virus to a major extent?

The presence of a suitable receptor that the virus can recognize and attach to.

What are examples of receptors that viruses can bind to?

  • Proteins
  • Carbohydrates
  • Glycoproteins
  • Lipids
  • Lipoproteins
  • Lipocomplex

What receptor does bacteriophage T4 bind to?

Bacteriophage T4 recognizes the carbohydrates in the LPS outer membrane of gram-negative bacteria.

How does the viral genome of a bacteriophage T4 enter the host cell?

DNA inside the bacteriophage heads is under high pressure, and because the interior of a bacterial cell is also under pressure from osmotic forces, the sheath contracts and the DNA is injected. Because of the high pressures this process only takes several minutes to complete.

What are weapons of bacteria and archaea agains viral attack?

  • Restriction modification system
  • Immune defense

What is the restriction modification system?

The restriction modification system consists of a restriction endonuclease enzyme and a methylase.
The restriction endonuclease enzyme cleaves double stranded DNA. The methylase adds a methyl group to a molecule. In restriction-modification systems of bacteria a methyl group is added to DNA at a specific site to protect the site from restriction endonuclease cleavage.

What is immune defense is bacteria?

Immune defense is the destruction of mRNA.

What is the viral defense against host attack?

Viral counter mechanisms to evade bacterial restriction systems. Two types are:
  • Chemical modification of viral DNA (methylation or glucosylation)
  • Production of proteins that inhibit host cell restriction system

What is the viral defense of a T4?

T4 adds a cytosine so that the host attack won't work anymore.

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