Viruses

Question 1

What is virology?

Answer 1

The study of viruses.

Question 2

What are viruses measured in?

Answer 2

Nanometres (nm)

Question 3

Are viruses cells, true or false?

Answer 3

False

Question 4

What are viruses composed of?

Answer 4

They are composed of protein with a piece of DNA or RNA inside.

Question 5

Viruses are obligate parasites. Explain what this means.

Answer 5

This means that they can only replicate themselves within a host cell.

Question 6

What are the five characteristics of life?

Answer 6

1. Organisation
2. Nutrition
3. Excretion
4. Response
5. Reproduction

Question 7

It can be argued that viruses only demonstrate two of the five characteristics of life. What are these two characteristics?

Answer 7

1. Organisation
2. Response

Question 8

(3 points)

How do viruses demonstrate organisation?

Answer 8

They demonstrate organisation because they consist of an organised protein coat and either DNA or RNA (never both), and sometimes possess an envelope made of lipids.

Question 9

How do viruses demonstrate response?

Answer 9

They demonstrate response because they respond to the surface antigens of living cells by attaching to proteins and either injecting their DNA/RNA or entering as a whole virus.

Question 10

Why do viruses not show nutrition?

Answer 10

They do not show nutrition as they do not metabolise food for energy production.

Question 11

Why do viruses not show excretion?

Answer 11

They do not show excretion as there are no direct waste products from viruses.

Question 12

Why do viruses not show reproduction?

Answer 12

They do not show reproduction because reproduction is the ability to propagate oneself, independently, within the species either by asexual or sexual reproduction. Viruses use a host’s nucleus and protein synthesis machinery to replicate themselves.

Question 13

(4 points)

What is the basic structure of a virus?

Answer 13

• A typical virus consists of a protein coat, called a capsid, along with a single piece of either DNA or RNA.
• Some viruses also have an outer layer of lipid and protein called a lipoprotein envelope, around the virus.
• This enables it to enter and leave cells much more easily.
• This is because the cell membrane of living cells is made from lipid and protein.

Question 14

Viruses are classified based on their shape. What are these shapes?

Answer 14

1. Rod shaped virus (tightly packaged helix)
2. Round virus
3. Complex virus

Question 15

(2 points)

What is an example of a rod shaped virus?

Answer 15

• Tobacco mosaic virus.
• Consists of proteins organised into a helical shape with DNA/RNA located in a groove within the helical structure.

Question 16

What is an example of a round virus?

Answer 16

Rhinovirus, which causes cold and flu.

Question 17

(2 points)

What is the structure of a round virus?

Answer 17

• Composed of 20 identical proteins arranged into a spherical protein coat.
• Many round viruses have a lipid envelope surrounding the protein coat.

Question 18

(2 points)

What is the most common type of complex virus?

Answer 18

• Bacteriophage.
• Bacteriophages infect bacteria.

Question 19

What are the five stages of viral replication?

Answer 19

1. Attatchment
2. Entry
3. Replication
4. Assembly
5. Release

Question 20

(4 points)

Explain the stage of attachment in viral replication.

Answer 20

• The virus binds to complementary proteins on the surface of a host cell.
• Viruses cannot attach to any cell they like. The cell has to have the correct proteins on its surface.
• Even with an organism, a virus might only be able to attach to certain types of cells.
• For example, the flu virus is capable of infecting only the cells of the nasal cavity and throat.

Question 21

Explain the stage of entry in viral replication.

Answer 21

The whole virus may enter the cell, or in the case of complex viruses, inject the DNA or RNA into the host cell.

Question 22

(2 points)

Explain the stage of replication in viral replication.

Answer 22

• The virus or virus DNA/RNA takes over the nucleus of the host cell and its ribosomes.
• The virus uses the host cell’s nucleus and ribosomes to make new viral proteins and viral DNA or RNA.

Question 23

Explain the stage of assembly in viral replication.

Answer 23

Thousands of new viruses are priced together by the host cell.

Question 24

(2 points)

Explain the stage of release in viral replication.

Answer 24

• New viruses are released from the host cell to go on and infect more cells.
• They can be released by bursting the host cell (killing it in the process) or by diffusing out or budding through the cell membrane.

Question 25

What are two examples of harmful viruses in humans?

Answer 25

1. Flu virus, which causes flu and colds 2. Rabies virus which causes rabies in humans

Question 26

# (3 points) What is rabies?

Answer 26

* Rabies is an animal virus that can infect humans. * It causes encephalitis (inflammation of the brain) and death soon thereafter. * It is widespread in wild canine animals on continental Europe.

Question 27

In what way have viruses been useful in transfering genes to cells?

Answer 27

Many types of viruses are used as vectors to transfer genes to cells.

Question 28

What are two examples of viruses used in genetic engineering?

Answer 28

1. SV40 virus - used in cancer research 2. Adeno-associated virus (AAV) - used in gene therapy research to deliver useful genes to tissues that lack a gene or a product of the gene.

Question 29

# (3 points) How could viruses be used as a potential substitute for anitibiotics?

Answer 29

* Research into bacteriopahges (viruses that infect and kill bacteria) is increasing. * It is hoped that they can be used as anti-bacterial agents. * In the future, bacteriophages may be used for cleanign surgical equipment, sterilising food, and treating bacterial infections in humans and plants.