Viruses

Question 1

What are viruses measured in?

Answer 1

nanometers (nm) as they are very small

Question 2

What 2 structures do all viruses have?

Answer 2

All viruses have a protein coat (capsid) that surrounds a nucleic acid. Viruses can have DNA or RNA

Question 3

Give an example of a virus with DNA as it’s nucleic acid

Answer 3

Bacteriophage

Question 4

Give an example of a virus with RNA as it’s nucleic acid

Answer 4

HIV (Human Immunodeficiency Virus)

Question 5

What is HIV comprised of? (It’s structure)

Answer 5

HIV viruses have an RNA core, surrounded by a protein capsid.
There is a lipid bilayer containing glycoprotein that surrounds the virus.
Within the core there is also RNA Transcriptase

Question 6

Describe the additional layer that surrounds the protein coat in HIV

Answer 6

A phospholipid bilayer (obtained from the human cell). Glycoproteins are present in this layer too

Question 7

What is the role of RNA reverse transcriptase?

Answer 7

The reverse transcriptase catalyses the synthesis of DNA from viral RNA

Question 8

What does the newly synthesised DNA then do in the progression of HIV infection?

Answer 8

The DNA codes for new protein coats (capsids) and viral RNA to make new viruses

Question 9

Why is HIV known as a retrovirus?

Answer 9

HIV contains RNA which is used as a template to make DNA

Question 10

What type of cell does HIV invade?

Answer 10

Human lymphocytes called helper T-cells. These T-cells are important in the immune response

Question 11

What is AIDS? How is it developed from HIV?

Answer 11

AIDS is a medical condition in which the immune system is critically compromised as a large amount of Helper T-cells are invaded by the HIV virus

Question 12

The structure of a bacteriophage

Answer 12

The nucleic acid core is DNA which is surrounded by a protein head.
There is a contractile sheath also made from protein.
There is a base plate with tail fibres

Question 13

What two structures of a bacteriophage are made of protein?

Answer 13

The protein head and the contractile sheath

Question 14

What type of cell does a bacteriophage infect?

Answer 14

Bacterial cells

Question 15

What does the DNA code for in a bacteriophage?

Answer 15

The production of new bacteriophage proteins

Question 16

What is the role of the tail fibres?

Answer 16

The tail fibres attach to the bacterial cells

Question 17

What is the progress of infection in a bacterial cell after it’s been infected by a bacteriophage?

Answer 17

The viral DNA synthesises new proteins heads (capsids).
The DNA will then replicate and package the new DNA into the new protein heads.
The bacterial cell is destroyed and will rupture to release the new viruses

Question 18

Why are viruses not true cells?

Answer 18

Viruses contain no cytoplasm or organelles. Viruses are also inert unless they have access to a living cell

Question 19

State 3 similarities between HIV and bacteriophages

Answer 19

• Very small
• Non-cellular
• Genetic material is within a capsid

Question 20

State 5 differences between HIV and Bacteriophages

Answer 20

•They have different shapes. Phages have tail fibres attached to a base plate
• HIV protein coat is within a phospholipid bilayer
• Glycoproteins are present in HIV but not in phages
• Bacteriophages normally contain DNA while HIV contains RNA
• HIV contains reverse transcriptase

Question 21

Why do most phages not contain reverse transcriptase

Answer 21

Most phages already have DNA which can replicate immediately