HIV life cycle - Snab Biology Topic 5

Virus life cycle - more specifically HIV

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HIV invades T Cells

Lysogenic viruses

  • Non-virulent virus inserts provirus (DNA) into host cell DNA to allow replication through cell division.
  • Repressor proteins from virus stop transcription of DNA to mRNA so provirus present in cell can stay dormant

Lytic viruses

  • Virulent virus inserts DNA/RNA into the cytoplasm of host cell (NOT INTO HOST CELL DNA)
  • Genetic information and proteins are replicated independantly including lysosome production which causes lysis when numerous newly produced viruses are ready to leave and infect more T lymphocytes
  • When lysogenic host cells become damaged the dormant viruses can be initiated and the lytic pathway occurs.

HIV cycle

Glycoprotein molecules (GP120) located on HIV envelope (cell surface) bind toCD4 receptors on T helper cells.

Binding allows HIV envelope to fuse with T cell surface membrance enabling viral RNA and enzymes/protein components to enter cell (not cell DNA)

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HIV hijacks host cell protein synthesis

Once inside cell cytoplasm, viral nuclear material must be turned from RNA to DNA to allow recognition from human system

  • Reverse transcriptase allows RNA to turn back into DNA
  • HIV is therefore a retrovirus - contains RNA and uses reverse transcription

Once viral DNA strand is produced integrase (enzyme from HIV) allows viral DNA to be integrated into host cell DNA.

Once genome is integrated normal protein synthesis (transcription/translation) can occur, producing new viral components and eventually causing lysis (as mentioned in the lytic pathway)


HIV (human immunodeficiency virus) destroys the body's immune system through T lymphocyte destruction leaving the body vulnerable to illnesses such as AIDS (Acquired Immune Deficiency Syndrome).

HIV causes AIDS and it is this infection that leads to death, not HIV alone.

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