Lecture 8 - viral genetics 2

Question 1

What do lysogenic viruses do?

Answer 1

integrate into the host rather than escape

Question 2

What happens when the genome is inserted into the host cell?

Answer 2

the genome can be integrated into the host cell chromosome

Question 3

What type of virus can carry out lysogeny?

Answer 3

lambda virus

Question 4

Describe the lytic pathway

Answer 4

1. Attachment
2. Injection
3. Viral DA replicated
4. Coat proteins synthesised
5. lysis (virus leave the cell)

Question 5

Describe the lysogenic pathway

Answer 5

1. attachment
2. injection
3. viral DNA is integrated into host DNA to create a lysogenized cell
4. cell division

Question 6

What can occur to the progeny of a lysogenized cell to make the cell join the lytic pathway?

Answer 6

induction

Question 7

When the virus is part of the lysogenized cell, what does it become?

Answer 7

it is still a virus, but not a virus particle - it is a genetic element

Question 8

What can occur after the host cell divides in a lysogenic pathway?

Answer 8

the progeny of division (the lysogens) can be induced to synthesise viral proteins

Question 9

What is a virus genome called?

Answer 9

prophage

Question 10

What is the role of repressor proteins during lysogeny?

Answer 10

The repressor prevents the forementioned process of induction
- inactivation of repressor or prevention of repressor synthesis INDUCES the prophase
- this results in lysis

Question 11

What occurs during the lysogenic replication cycle?

Answer 11

• during lysogeny in y phage, the virus genome is integrated into host chromosome
• the host undergoes normal cell division

Question 12

How is y (lambda) integrated into the host DNA?

Answer 12

• has double stranded DNA that is linear
• the viral genome integrates at the attachment site att(y)
• in order for the viral genome to be integrated it requires an enzyme - (y) integrase

Question 13

What enzyme is required to integrate y into the host DNA?

Answer 13

y integrase

Question 14

What does integrase do?

Answer 14

integrase cuts at the att site, which allows splicing to occur and the lamba (y) genome can be integrated

Question 15

How is the linear DNA of the y virus be made circular?

Answer 15

this occurs by using cohesive ends. The cuts in the host chromosome is compatible with the cuts made in the viral genome

Question 16

What occurs in the lytic cycle?

Answer 16

the viral genome must be replicated ready for packaging and release from the host

Question 17

In the lytic pathway how many copies of the viral genome must be replicated?

Answer 17

multiple

Question 18

What technique is used for making lots of copies?

Answer 18

rolling circle replication

Question 19

Describe rolling circle replication

Answer 19

1. strand of the circular lambda genome is nicked - a long single-stranded concatamer is made, using the unbroken strand as a template
2. a second strand is made, using the single-stranded concatamer as a template - the double-stranded concatamer is cut into genome-sized lengths at the COS sites, giving cohesive ends

Question 20

What do some animal viruses have as well as a capsid?

Answer 20

• may have a membrane
• also more complex as eukaryotic cell have nucleus

Question 21

Why is it a challenge for viruses if they have RNA genomes?

Answer 21

this can cause problems as the host cell may not be used to doing so.

Question 22

What do some virus do when leaving the host following lysis?

Answer 22

take some of the host membrane

Question 23

What can prokaryotes do that eukaryotic cells can’t?

Answer 23

eukaryotic cells can’t create multiple proteins from strand of DNA, whereas prokaryotes can.

Question 24

Can polycistronic mRNA be translated into eukaryotes?

Answer 24

no

Question 25

Why can polycistronic mRNA not be translated by in eukaryotes?

Answer 25

eukaryotic have a 5’ cap and poly A tail on their DNA, whereas prokaryotes don’t

Question 26

How do prokaryotes translate their mRNA?

Answer 26

by tricking the eukaryotes

Question 27

What does the prokaryotes need to deal with if it wants to survive in the host?

Answer 27

eukaryotes goes through capping, splicing and polyadenylation

Question 28

Describe (+) strand RNA viruses of animals

Answer 28

• typically these are vey small (approx. 30nm) except coronavirus - can cause problems for coding capacity
• e.g. polio, rhinovirus (common cold), hepatitis A

Question 29

Describe Polio virus - it has multiple coding sites

Answer 29

• polio has a single linear ssRNA genome
• the genomic RNA also acts as the mRNA but note that there is no capping (there is a tail)
• instead the RNA at the 5’ end folds into stem-loops and has a protein - Vpg bound - mimics a cap
• this leads to translation as it is treated as an mRNA as a host cell

Question 30

What common strategy is adopted by viruses to create many copies at once?

Answer 30

viral protein is synthesised as one large poly protein

Question 31

What happens to the poly protein are it is synthesised?

Answer 31

• the poly protein can then be cut into functional units after
• the virus then can make its own protease, structural cost proteins and RNA replicase

Question 32

Why do viruses make their own RNA replicase?

Answer 32

allows copies of its own genome (as it is RNA)

Question 33

What occurs to the genome after the functional units have been produced?

Answer 33

the genome can also be replicated, and a copy is made of the (+) strand - this bit of the strand that actually makes the protein

Question 34

What types of strands are made?

Answer 34

Positive strand is made, before being translated into a negative strand via RNA replicase. A positive strand is then made from this also using RNA replicase.

Question 35

Where does replication occur?

Answer 35

replication (which doesn’t involve DNA) can occur in the cytoplasm

Question 36

Why is the host RNA & protein synthesis inhibited?

Answer 36

because the host cap-binding protein