From The Student Room

TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Biology > Virii

---

• Viruses are not truly alive.

• They are much smaller and less complex than cells.

• Most viruses multiply exclusively inside living host cells.

• Viruses cause disease by the sum of the effects of damage to the host cells they invade and the effects of toxins which are produced in the process.

• They are DNA or RNA in a protein coat (capsid).

• They have no nucleus, cytoplasm, or membranes.

• They do not carry out cellular functions.

• Viruses contain very few enzymes and so, as intracellular parasites, they uses the host's enzymes for their own metabolism.

• Viruses are unable to move and so rely on passive dispersal, or a vector, to move them between host cells.

• Viruses reproduce by binding to specific cells, penetrating the cell membrane and then using the protein making machinery (transcription and translation) of the cell to build fresh viruses.

• DNA viruses, e.g. smallpox, do not mutate and can be transcribed directly.

• RNA viruses, e.g. AIDS, mutate regularly - have to be reverse-transcribed back to DNA.

Comments