Topic 2 - Viruses

Question 1

meaning obligate intracellular parasites

Answer 1

can only exist and reproduce as parasites in the cells of other living organisms

Question 2

how do viruses differ

Answer 2

• variation in the genetic information
• structure of their protein coat
• whether or not they have a envelope

Question 3

what is a protein coat/ capsid made out of

Answer 3

made up of capsomeres arranged in different ways

Question 4

what is the advantage of using repeating units

Answer 4

it minimises the amount of genetic material needed to code for coat production

Question 5

what is the advantage and disadvantage for viruses to have a liîd envelope

Answer 5

• makes it easier for viruses to pass from cell to cell
• makes viruses vulnerable

Question 6

how do viruses attach to their host cells

Answer 6

by specific antigens known as Virus Attachment Particles (VAPs)

Question 7

how do VAPs attach the virus to its host cell

Answer 7

They bind themselves to specific receptor proteins in the hosts plasma membrane, to help the virus attach

Question 8

what are the 2 types of genetic information

Answer 8

DNA and RNA

Question 9

what are the 2 types of nucleic acid

Answer 9

double-stranded and single-stranded

Question 10

How do DNA viruses make new viruses in the host cell

Answer 10

The viral DNA acts directly as a template for the viral DNA and the mRNAs needed to induce synthesis of viral proteins.

Question 11

Give 2 examples of DNA viruses

Answer 11

• smallpox virus
• adenovirus

Question 12

what are ssRNA viruses

Answer 12

RNA viruses that contain a single strand of RNA

Question 13

what are the 2 types of ssRNA viruses

Answer 13

Positive ssRNA viruses
Negative ssRNA viruses

Question 14

How do positive ssRNA viruses make new viruses in the host cell

Answer 14

The RNA is used directly as mRNA for translation into proteins at the ribosomes. The ribosomes made include viral structural proteins and an RNA polymerase, which is used to replicate the viral RNA

Question 15

Give 2 examples of positive ssRNA viruses

Answer 15

• Tobacco Mosaic Virus
• Hepatitis C

Question 16

How do negative ssRNA viruses make new viruses in the host cell

Answer 16

The RNA must first be transcribed into a sense strand before it can be used to make viral proteins and more RNA. The virus imports RNA replicase, which transcribes the antisense strand into a sense strand using free bases from the host cell. This sense strand then acts as mRNA at the ribosomes, coding for viral proteins, including RNA replicase. These proteins combine with replicated RNA to form new viral particles.

Question 17

give 2 examples of negative ssRNA viruses

Answer 17

• Influenza
• Ebola

Question 18

What is the difference in structure between RNA viruses and RNA retroviruses

Answer 18

RNA retroviruses have a protein capsid and a lipid envelope

Question 19

How do RNA retroviruses make new viruses in the host cell

Answer 19

the single strand of viral RNA directs the synthesis of the enzyme reverse transcriptase, which makes DNA molecules corresponding to the viral genome. This DNA is incorporated into the host cell DNA and used as a template for new viral proteins and viral RNA genome

Question 20

what are natural viruses

Answer 20

viruses that cause disease and attack every other type of living organism

Question 21

what are bacteriophages

Answer 21

viruses that attack bacteria

Question 22

how do bacteriophages get into the bacteria cells

Answer 22

they inject their genome into the host cell, but the bulk of the viral material remains outside the bacterium. The viral DNA forms a plasmid within the bacterium

Question 23

how do viruses that infect animals get into the cells

Answer 23

• the virus is taken into the cell by endocytosis and the host cell then digests the capsid, releasing the viral genetic material
• the viral envelope fuses with the host cell surface, releasing the rest of the virus into the cell membrane

Question 24

how do plant viruses get into plant cells

Answer 24

get into the cells by using a vector

Question 25

give and example of a vector

Answer 25

an aphid (an insect) can pierce the cell wall

Question 26

what are the 2 different pathways a virus can infect the host cell by

Answer 26

• the lysogenic pathway
• the lytic pathway

Question 27

explain what happens to a DNA virus when it follows the lysogenic pathway

Answer 27

the virus inserts its DNA into the host DNA so it’s replicated every time the host cell divides. During this period of lysogeny, the virus is latent and does not affect the host cell

Question 28

why is messenger RNA not produced from the viral DNA when a DNA virus enters the lysogenic pathway

Answer 28

because one of the viral genes causes the production of a repressor proteins that make it impossible to translate the rest of the viral genetic material

Question 29

what is a provirus

Answer 29

the DNA inserted into the host

Question 30

explain what happens to a virus when it follows the lytic pathway

Answer 30

The viral genetic material is replicated independently of the host DNA after entering the host. Mature viruses are made and the host cell bursts, releasing the new virus particles to invade other cells.

Question 31

What is the virus known as when in the lytic pathway

Answer 31

virulent

Question 32

when do viruses in the lysogenic state become virulent

Answer 32

when the host is damaged, the amount of repressor protein decreases and the virus enters the lytic pathway

Question 33

what do positive ssRNA viruses contain

Answer 33

single strand of RNA that is a sense strand

Question 34

what do negative ssRNA viruses contain

Answer 34

single strand of RNA that is an antisense strand

Question 35

give 2 examples of RNA retroviruses

Answer 35

• HIV: causes AIDS
• Rous sarcoma: causes cancer in chickens