Virii
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• 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.

Other Notes in this Category

1. Abortion Methods
2. Atmosphere and Pollution
3. Bacteria
4. Composition of Blood - Plasma, White Blood Cells, Red Blood Cells and Platelets
5. Down Syndrome
6. Enzyme Quiz
7. Fungi
8. Hereditary Diseases
9. Respiration and Osmosis
10. The Defences of the Human Body
11. The Heart Beat
12. Virii

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