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Infection, immunity and repair > Viral replication > Flashcards

Viral replication Flashcards

1
Q

What is the role of the viral envelope and capsid outside the cell?

A

Protect the virus from extreme conditions

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2
Q

What is the role of the viral envelope and cpasid inside the cell?

A

Recognises target cell

Protects virus from the innate immune system

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3
Q

What does virus do when it encounters a host cell?

A

Virus recognises cell and binds to it

Virion disassembly

Genome delivered into cell - directly of taken in and delivered downstream

Genome replication

Gene expression to produce viral proteins

Virion assembly - viral particles are constructed and released

Adjacent cells become infected

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4
Q

What type of replication is viral replication?

A

Cyclic

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5
Q

How are viruses transmitted?

A

Aerosols - mucus droplets

Blood - vectors

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6
Q

What are the two challenges to virus entry?

A

Recognising cell

Crossing the membrane

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7
Q

How do viruses recognise cells?

A

By identifing cell membrane receptors

If no appropriate receptor on cell - virus won’t infect it

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8
Q

What do cell surface proteins define?

A

Define the tropism of a cell

If binding of virus onto receptor does not cause viral replication - virus won’t bind to it

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9
Q

What happens when viruses binds to cell surface proteins?

A

Cell surface proteins activate intrinsic mechanisms in the cell

Regulate replication mechanisms with in the cell

Virus exploits the properties of these proteins

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10
Q

What are the two ways in which viruses enter a host cell?

A

Virus fuses or penetrates cell membrane

Virus is internalised by endocytosis

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11
Q

What determines the pathway of entry of a virus?

A

Whether the virus is enveloped or not

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12
Q

Entry of a non-enveloped virus

A

Structure of virion changes once bound to CSM

Proteins that make up the capsid move relative to each other

Hydrophobic sequence of peptides are exposed

Penetrates the membrane-
produces a pore

Genome is injected

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13
Q

What mechanism of virus entry do non-enveloped viruses use?

A

Form pores in the CSM

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14
Q

What is a non-enveloped virus that enters the host cell via formation of pores in CSM?

A

Polio

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15
Q

Entry of an enveloped virus

A

Viral envelope = lipid

Viral envelope fuses and become continuous part of the cell membrane

Contents of the virion are internalised into endosome

Endosome moves into the cell

Down the veiscular transport pathway

Luminal pH decreases

Release of capsid into the host cell

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16
Q

What protein on viruses bind to CSM of host cells?

A

Haemagglutinin

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17
Q

What do Haemagglutinin proteins on viral particles bind to on host cells?

A

Sialic acid

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18
Q

What is an endosome?

A

Membrane bound compartments

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19
Q

What happens as the endosomes move into the cells?

A

Endosomes formed by the CSM of the host

Luminal pH decreases

pH of 5.5 - Haemagglutinin complex undergoes conformational change and transition

This causes a thrusting motion

Target membrane and Haemagglutinin fuse

Releases capsid

20
Q

Basics of gene expression

A

DNA -> transcribed -> mRNA

By RNA polymerase

mRNA -> translated by ribosomes -> produce proteins

21
Q

How do viruses replicate?

A

Use the protein synthesis machinery of host cells

22
Q

What is the Baltimore classification?

A

Deduced the relationship between viral genome and mRNA

mRNA = + sense

In order to make proteins, have to make mRNA first

Divides the viruses into 7 classes depending on their DNA sequence

23
Q

Why do viruses have to make mRNA in order to replicate?

A

Central dogma

DNA -> mRNA -> proteins

Since viruses have to use the host replication machinery, it has to make mRNA in order to replicate

24
Q

What sense is mRNA?

A

Positive stranded

25
Q

What are the different types of genome in viruses?

A

Double stranded DNA

Single stranded DNA

Double stranded RNA

Positive single stranded RNA

Negative single stranded RNA

Single stranded RNA reverse transcriptase

Double stranded DNA reverse transcriptase

26
Q

How do double stranded DNA viruses make viral proteins?

A

Transcription of the - strand of DNA to form + mRNA

This is then translated to from viral proteins

DNA-dependent DNA polymerase

27
Q

How do single stranded DNA viruses make viral proteins?

A

Replicate the single stranded DNA to make double stranded DNA

Transcription of the - strand of DNA to form + mRNA

This is then translated to form viral proteins

28
Q

How do double stranded RNA viruses make viral proteins?

A

If you break down the double stranded RNA you have:

Negative stranded RNA

Positive stranded RNA

Positive strand RNA can be used directly as mRNA to form viral protein

Negative strand can be used as a template to make more positive strands

29
Q

How do single positive stranded RNA viruses make viral proteins?

A

Could use positive stranded RNA as mRNA

But - have to produce a lot of viruses

So in order to increase viral load:

Positive stranded RNA serve as a template

Form negative stranded RNA template

The negative stranded RNA template forms lots of positive stranded RNA

Some are used as mRNA to make viral proteins and some are used as genetic material

30
Q

How do single negative stranded RNA viruses make viral proteins?

A

Use single negative stranded RNA as a template

Produce positive stranded mRNA

RNA-dependent RNA polymerase

31
Q

When is RNA-dependent RNA polymerase used?

A

Going from RNA to RNA

32
Q

When is DNA-dependent RNA polymerase used?

A

Going from DNA to RNA

33
Q

How do single stranded RNA reverse transcriptase viruses make viral proteins?

A

Use single stranded RNA to produce DNA single strand

Use reverse transcriptase enzyme

This is a DNA hybrid - one RNA strand and one DNA strand

RNA strand in double stranded helix can be removed using enzymes

Two DNA strands come together to form double helix

Insert into the genome of the host

DNA-dependent RNA polymerase is used to make mRNA

mRNA is transcribed to make viral proteins

34
Q

How do double stranded DNA reverse transcriptase viruses make viral proteins?

A

Start with double stranded DNA

Take a strand of DNA transcribe it to make positive sense RNA

RNA is then reverse transcribed to form double stranded DNA

DNA-dependednt RNA polymerase is used to make mRNA

mRNA is transcribed to make viral proteins

35
Q

What is the genome of the Herpes simplex virus?

A

Double-stranded DNA

36
Q

What is the structure of a Herpes simplex virus?

A

Contains double-stranded DNA genome

Surrounded by tegument

Tegument contains proteins on its surface (VP16)

37
Q

What is an important tegument protein?

A

VP16

Regulates gene expression

38
Q

Describe process of Herpes virus replication

A

VP16 on tegument enters host cell

VP16 has a nuclearlocalisation signal and traffics to the nucleus

Binds to DNA promoter sequences

Promoter sequences happen in 5 places of the viral genome

VP16 binds to sequences of DNA and recruits host transcription machinery

Transcription initiates in these 5 genes

39
Q

What do the 5 genes on the Herpes genome that are transcribed code for?

A

These genes regulate subsequent gene expression machinery

Early genes express DNA replication machinery

Late genes express structural proteins

40
Q

What are the bases that code for promoters?

A

TAATGARAT

41
Q

What is the genome of the polio virus?

A

Positive sense RNA virus

42
Q

Describe the process of viral replication in polio

A

Virus enters and recruits ribosomes by IRES at 5 prime end of the genome

Ribosome binds directly to the mRNA

Genome is translated

Translation forms 3 large single protein molecules as well as protease

Protease claves polyproteins into smaller units that form:

Part of the virus
RNA polymerase that replicates the genome

43
Q

Difference between Polyomaviruses and Herpes viruses?

A

Polymaviruses - recruits host machinery

Herpes virus - encodes polymerase and accessory proteins (polymerase, helicase, primase)

Get same outcome

44
Q

How are viruses released?

A

Some bud through membranes automatically - budding

Some kill the cell and release contents via cell lysis

Some bud across the membrane like endosome - exocytosis

45
Q

What are two ways in which viruses are assembled?

A

Virus encodes scaffold proteins and particles are assembled around that

Virus factories form bringing proteins together

Infection, immunity and repair (52 decks)

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