MICR 2420 Lecture 6: 6
8 Dec 2019
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Chapter 6: Viruses
Virus
• A virus is a non-cellular particle or virion, that must infect a host cell, where it
reproduces
• Martinus Beijerinck & Dmitri Ivanosky first proposed their existence
• First crystallization of virus , Tobacco Mosaic Virus (TMV) – Wendell Stanley
• Found soluble infectious agents that passed through a filter too small too allow the
passage of cells
Viruses can be useful
• Bacteriophage can be used to control infections or biofouling as an alternative to
antibiotics or disinfectants
• Viruses can be modified as delivery vehicles for gene therapy
• Bacteriophages can be used in molecular cloning, as cloning vectors
• Filamentous phage particles can be used to crystalize conducting nanowires
Virus integrate their own genome into the host genome
• Prophage: a virus that integrates its genome into the DNA of bacterial genome
• Provirus: an integrated viral genome within a human cell
• Endogenous virus: a permanently integrated provirus transmitted through the germ line
Is a virus a living organism?
• Virion or virion particles
-an inert particle consisting of nucleic acid enclosed by a protein capsid, some has
enzymes and lipid envelope
-No metabolism or energy conversion (argues that viruses are nonliving)
• Intracellular replication complex
-within in the host cell, viral genome direct the cell’s enzyme to assemble progeny
virions at virus factories (replication complexes)
• Viral genome integrated within host DNA
-some viral genome may integrate within a host chromosome and replicate a part of the
host
• Virion assembly process argues that they are living organisms
• Genome of large virus
-Chlorovirus shows evidence of evolutionary loss of genes from a cell
