L13 Virus Replication

Question 1

What are the six steps of virus multiplication?

Answer 1

Attatchment
Penetration
Uncoating
Biosynthesis
Assembly
Release

Question 2

What does the entry to a host cell depend on?

Answer 2

The interaction between viral surface proteins and host cell surface proteins
= VIRUS RECEPTOR

Question 3

What processes occur in the biosynthesis step of virus multiplication?

Answer 3

Genome replication
mRNA synthesis
Translation

Question 4

What do viruses require for biosynthesis?

Answer 4

Host ribosomes, enzymes and precursors

Question 5

Attachment slide listen

Answer 5

Specific binding of a virus-attatchment protein to a cellular receptor molecule on the host cell surface

Question 6

How are you DNA virus genomes replicated and transcribed?

Answer 6

By host polymerases
Replicated by host DNA polymerases
Transcribed by host RNA polymerases

Question 7

Why can’t RNA virus genomes use host polymerases to replicate and transcribe? What do they do instead?

Answer 7

Because host polymerases can only use DNA as a template

Therefore RNA viruses must encode their own polymerases which can use RNA as a template

Question 8

What is the function of the proteins encoded by the virus genome?

Answer 8

• replication of the genome
• package the genome into virus particles
• alter the metabolism of the infected cell

Question 9

What is the different between structural virus proteins and non-structural virus proteins?

Answer 9

Structural - form part of the virus
Non-structural - not incorporated into the virus particle

Question 10

Why must viruses compete for host cell ribosomes?

Answer 10

Because viruses don’t carry their own ribsomes

Question 11

What is the translation of most viral mRNAs dependant on?

Answer 11

The 5’ terminal cap

Question 12

What do eukaryotic initiation factors bind to?

Answer 12

Bind to the cap and 40S ribosomal subunit

Question 13

Outline post translational modification in viruses

Answer 13

• viral proteins undergo the same range of post translational mods as the host cell proteins e.g. acylation
• some virus genomes are translated to produce a single large viral poly protein which must be post-translation ally cleaved to release individual viral proteins

Question 14

How do most enveloped viruses acquire the envelope?

Answer 14

By budding through the plasma membrane
- may also bud from the nucleus e.g. herpes

Question 15

Outline the process of acquiring membrane and surface glycoproteins by enveloped viruses

Answer 15

• synthesis and co-translational membrane insertion of viral glycoproteins
• glycosylation starts in the RER
• there are vesicles which contain viral glycoproteins
• glycosylation continues in the Golgi apparatus
• viral glycoproteins are transported to plasma membrane in vesicle
• host glycoproteins in plasma membrane become part of the envelope
• nucleocapsid forms and it migrates to virus-modified membrane
• budding starts and a budding virion is formed
• results in a free infectious virus

Question 16

How can the virus be released?

Answer 16

• by cell lysis
• by budding from plasma membrane or into lumen of ER
• spread from cell to cell via pored or by inducing fusion of their membranes
• released preceded by or followed by a maturation step

Question 17

Summarise primary site replication

Answer 17

1) virus binds to cell-surface receptor and enters celll by fusion from without or receptor mediated endocytosis
2) viral genome must be replicated and transcribed into mRNA
3) viral proteins are translated and modified using host cell machinery
4) virions are released from cell by budding, cell lysis or cell to cell spread

Question 18

How can viruses shed?

Answer 18

Directly from the site of primary replication
OR
Spread through the body to cause a systemic infection

Question 19

What are bacteriophages?

Answer 19

Viruses which infect bacteria

Question 20

Describe a M13 filamentous bacteriophage

Answer 20

• circular ssDNA
• cloning and DNA sequencing
• released without losing host cell
• budding makes own channel

Question 21

What makes up a tailed phage structure?

Answer 21

Head - includes DNA
Collar
Tail
Long tail fibres
Base plate
Lysozyme complex
Protein needles

Question 22

Why are bacteriophage important?

Answer 22

• can turn bacteria virulent
• alternative to antibiotics : phage therapy
• great tool in the lab for recombinant DNA technology

Question 23

Which plasma protein does HIV hijack?

Answer 23

CCR5 which has a function of being a chemokine receptor

Question 24

Which plasma protein is hijacked by rhinovirus?

Answer 24

ICAM-1 which has the function of Intracellular adhesion molecule

Question 25

What plasma protein is hijacked b7y the rabies virus?

Answer 25

Acetylcholine receptor which is a neuronal signal transducer

Question 26

Which plasma protein is hijacked by the measles virus?

Answer 26

CDW150 (SLAM) which activates lymphocytes

Question 27

Which plasma protein is hijacked by SARS-CoV-2 (Covid-19)

Answer 27

Angiotensin-converting enzyme 2 which matures angiotensin which involves vasoconstriction and blood pressure

Question 28

In the internalisation step, describe fusion from without

Answer 28

The process in which particles of some enveloped viruses can direct fusion of target cells in the absence of viral replication

Question 29

What is receptor mediated endocytosis?

Answer 29

A process in which viruses can enter or leave an animal cell

Question 30

What happens in the lytic cycle of a bacteriophage?

Answer 30

Hijacks and overrides host cell machinery
- excision and hijack

Question 31

What happens in the lysogenic cycle of a bacteriophage?

Answer 31

Hitchhikes and gets photocopied
- undergoes environmental or cellular changes

Question 32

What allows the binding of the coreceptor in the attachment stage?

Answer 32

A conformational change in gp120 allowing binding of the coreceptor

Question 33

What leads to an interaction with the host cell membrane in attatchment stage?

Answer 33

A conformational change in gp41
-> leads to membrane fusion