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The lifecycle of a virus

Health, disease and the development of medicines · Pathogens and infections · note 4 of 5

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The lifecycle of a virusSpec 5.7B

Viruses are not cells and cannot reproduce on their own. They reproduce inside a host cell, using the host's cell machinery. A virus can follow one of two pathways.

The lytic pathway

  1. The virus attaches to a host cell and its genetic material enters the cell.
  2. The viral genetic material takes over the host cell and the cell makes new virus parts.
  3. New viruses are assembled inside the cell.
  4. The cell bursts open (it is lysed) and the new viruses are released to infect other cells.

The lysogenic pathway

  1. The virus attaches and its genetic material enters the host cell.
  2. The viral genetic material becomes part of the host cell's DNA.
  3. The virus stays dormant (inactive). The host cell does not burst and does not show harm. When the host cell divides, the viral genetic material is copied too, so every new cell contains it.
  4. At a later time, something may trigger the viral genetic material to become active, and the virus then follows the lytic pathway.
Lytic and lysogenic pathways compared
LyticLysogenic
Viral genetic materialTakes over the cell straight awayJoins the host DNA and stays inactive
New viruses made?Yes, immediatelyNot until the virus becomes active
Host cellBurst open and killedSurvives and divides, copying the viral genes
Diagram of a virus attaching to a host cell and injecting its genetic material, then the lytic pathway (new viruses made, cell bursts and releases them) and the lysogenic pathway (viral genetic material joins host DNA, cell divides copying it, and a later trigger switches it to the lytic pathway).Tap to enlarge
Lytic: new viruses are made and the cell bursts. Lysogenic: viral genes hide in the host DNA until a trigger makes them active.