Viral Rep And Infection

Question 1

What do viruses bind to first on host cells and why (via their surface proteins)

Answer 1

Bind to low affinity receptors (proteoglycans)

This increases likelihood of them binding to primary receptors

Question 2

What are co receptors

Answer 2

Receptors which in some cases eg hiv are needed to be bound to aswell as primary receptors for fusion of membrane with envelope

Question 3

Which low affinity proteoglycans does HIV bind to

Answer 3

Heparin sulfate

Question 4

What is the primary receptors for hiv which glycoprotein 120 binds to

Answer 4

CD4

Question 5

What does gp120 CD4 binding allow

Answer 5

Conformational changes in virus which unveils chemokine coreceptor binding site it can bind to

Question 6

What are the 2 coreceptors hiv binds to

Answer 6

Ccr5

Cxr4

Question 7

What happens when gp41 binds to ccr5 or cxr4 in hiv attachment

Answer 7

Fusion of cell membrane with the envelope causing release of nucleocapsid

Question 8

Are all receptors protein

Answer 8

No

Some are carb or lipids

Question 9

What is the process called where non enveloped viruses get internalised (envelope can’t fuse with membrane)

Answer 9

receptor mediated endocytosis

Question 10

How can non enveloped and enveloped viruses be internalised via receptors endocytosis

Answer 10

attach to the surface via gp/ surface proteins

These then get internalised into a vesicle from the membrane of the cell

Vesicle then fuses with endosome and causes lowered ph

This causes conformational shape in virus and released

Question 11

What is the difference between enveloped release from vesicle and non enveloped via ph change

Answer 11

Enveloped allows fusion of envelope with vesicle and nucleocapsid released

Non enveloped form in pores in the vesicle and nucleocapsid released

Question 12

How many classes of virus are there due to Baltimore classification (genome Rep and mrna production)

Answer 12

7

Question 13

Name the 5 main types of viral genome

Answer 13

Ds dna

Ss dna

Ds rna

Ss rna (+)

Ss rna (-)

Question 14

What is the difference between ss rna + and -

Answer 14

+ means it uses the sense strand so needs reverse transcriptase

• means it uses anti sense so can use polymerase as normal

Question 15

Which enzymes do dna viruses use for rep and transcription

Answer 15

Dna and rna polymerase from host

Sometimes own

Question 16

Which enzyme do viruses need to produce if they have rna (-) antisense

Answer 16

Rna dependant rna polymerase for both rep and transcription

Question 17

Which enzyme is needed for rna + sense strand viruses

Answer 17

Reverse transcriptase

Question 18

What are structural proteins translated via virus

Answer 18

Proteins needed to form virion eg capsomeres

Question 19

Give an example of non structural proteins translated for virus

Answer 19

Proteins for genome replication eg rna dependant rna polymerase

Question 20

Where do viruses get ribosome needed for translation

Answer 20

Host cell

Question 21

What do most viruses need in translation similar to eukaryotes and why is it needed

Answer 21

5’ cap

Allows 40s subunit binding and also initiation factors for translation

Question 22

How is IRES used to allow viruses to translate without 5’ cap

Answer 22

Viral rna will form a secondary structure similar to the 5’ cap which means IF and ribosome can bind

Question 23

Name some modifications viral proteins can undergo post translation

Answer 23

Glycolysation, acylation

Question 24

Sometimes viral genomes translate into a large poly protein which is then cleave by which enzyme to form things like structural capsomeres

Answer 24

Proteases

Question 25

Where are proteins glycosylated to form viral glycoproteins

Answer 25

RER

Question 26

Where are the new viral glycoproteins transferred to via vesicles after productjon in RER

Answer 26

Membrane of cell

Question 27

How does budding allow an envelope and also glycoproteins to be found on viruses

Answer 27

The nucleocapsid is wrapped in the cell membrane with the viral glycoproteins and this forms the lipid envelope

Question 28

Other than the cell membrane , how else is the lipid envelope acquired

Answer 28

RER or nucleus

Question 29

How do non enveloped viruses get released

Answer 29

Cell lysis

Question 30

How can viruses spread cell to cell

Answer 30

Through pores or membrane fusion

Question 31

What is it called when viruses spread to a secondary site in blood

Answer 31

Primary viraemia

Question 32

What is another word for transmission after release

Answer 32

Shedding eg via lungs respiratory

Question 33

What is secondary viraemia

Answer 33

When viruses spread to target organs either the ones originally infected or other via the blood form the secondary site

Question 34

Which site of the body has no Shedding of the body from this target organ

Answer 34

The brain (no transmission)