Viruses

Question 1

1. Cells are measured in micrometers (um), what are viruses measure in and why?

Answer 1

Viruses are measured in nanometers (nm) as they are very small.

Question 2

3. Give an example of a virus with DNA as its nucleic acid core

Answer 2

bacteriophage

Question 2

2. What 2 structures do all viruses have?

Answer 2

All viruses have nucleic acid within a protein coat (capsid)

Question 3

4. Give an example of a virus with RNA as its nucleic acid core

Answer 3

HIV (human immunodeficiency virus)

Question 4

5. Learn the structure of a bacteriophage

Answer 4

1-protein head 2-DNA 3-contractile sheath (protein) 4-tail fibre(s) 5-base plate

Question 5

6. Name two structures of the bacteriophage made of protein

Answer 5

The head and the contractile sheath

Question 6

7. What type of cell does a bacteriophage infect?

Answer 6

Bacterial cells

Question 7

8. What does the DNA code for in bacteriophages?

Answer 7

The production of new bacteriophage proteins that form the capsid (head)

Question 8

9. What is the role of the tail fibres?

Answer 8

The tail fibres are important in attaching the virus to bacterial cells

Question 8

10. What does a bacteriophage do after it infects a bacterial cell?

Answer 8

• Produces bacteriophage proteins from the DNA (for new bacterial coats). Replicates the DNA * Packages the new DNA into the new protein coats * Bacterial cell is destroyed as it ruptures when releasing the new viruses

Question 9

12. Describe is the additional layer that surrounds the protein coat in HIV?

Answer 9

A lipid bilayer containing glycoprotein

Question 9

11, Learn the structure of HIV

Answer 9

1-glycoprotein 2-reverse transcriptase enzyme 3-RNA 4-phospholipid bilayer obtained from human cell parasitised before release of virus 5-protein

Question 10

13. Where is this lipid bilayer obtained from in HIV?

Answer 10

The phospholipid bilayer is obtained from the human cells infected before the release of the virus

Question 11

14. Why does HIV deliver the enzyme reverse transcriptase into the host cell?

Answer 11

The reverse transcriptase catalyses the synthesis of DNA from RNA. This DNA is then used to synthesis new prote coats and viral RNA.

Question 12

15. Why is reverse transcriptase not required in bacteriophages?

Answer 12

DNA is already present

Question 13

16. What type of human cells does HIV invade?

Answer 13

A type of lymphocyte called helper T-cells

Question 14

17. What is AIDS (acquired immunodeficiency syndrome)?

Answer 14

AIDS is a medical condition in which the immune system is critically compromised as progressively more T- cells are destroyed by the HIV virus.

Question 15

18. Why are viruses not true cells?

Answer 15

• No cytoplasm * No organelles * Inert without access to a living cell

Question 16

19. State 3 similarities between HIV and bacteriophages

Answer 16

• Very small * Non-cellular * Genetic material within a protein coat

Question 17

20. State 5 differences between bacteriophages and HIV?

Answer 17

• Different shapes and only phage have tail fibres attached to a base plate * In HIV the protein coat (head/capsid) is within a phospholipid bilayer. There is no lipid bilayer in phages. * Glycoproteins are present in HIV not in phages * Bacteriophages normally contain DNA while HIV contains RNA * HIV contains reverse transcriptase (no reverse transcriptase in phages)