L9 Viral replication

Question 1

Many thousands of viruses can enter a host, few are able to infect and replicate. In the first few hours there is little apparent activity, however appearances are deceptive, and which cell processes are proceeding:

Answer 1

• Transcription of viral genes to form viral mRNA
• Translation of viral genes to produce early viral proteins; including enzymes to replicate vDNA or vRNA
• Early phase is called the eclipse phase
• In the productive phase which follows, new virus particles produced and released from cell

Question 2

First step in Viral infection: Entry into host cell

Answer 2

Animal viruses attach to specific cells and can spread to multiple tissues. Entry into host cell is usually dependent on virus attachment to a host cell molecule: the viral receptor

Question 3

Classical Virus Replication Cycle

Answer 3

Molecular events during each stage of the virus replication cycle
* Viral entry
* Replication
* Assembly
* Egress/leaving

Question 4

(1) Viral entry: Attachment to receptor with HiV example

Answer 4

• HiV gp120 is bound to cellular receptor CD4 through noncovalent intermolcular forces and occur because of shape complementarity.
• Tight binding is irreversidble because it triggers host cell to internalise the virus.

Question 5

(2) Penetration of human immunodeficiency virus (HIV) to cell.

Answer 5

• After HiV binds to CD4 there is conformational change in HiV gp120 and will bind to co-receptors like CCR5
• HiV gp41 will rearrange to expose fusion peptide
• Fusion peptide will insert into host cell
• Gp120 undergoes more conformational change and allows fusion peptide to form a pore between virus interior and host cell cytoplasm.

Question 6

Different viral components are synthesized during an infection in what order?

Answer 6

1. Viral mRNA
2. Viral proteins
3. Viral genomes
4. intracellular viruses
5. Extracellular virsuses

Question 7

Following entery to a susceptible cell viruses must synthesis ____ to expose viral proteins.

Answer 7

mRNA

Question 8

[Formation of viral mRNA] All viruses must:

Answer 8

1. Produce viral structure proteins
2. Replicate their viral genomes

Question 9

[Formation of viral mRNA] Virus must make what that is able to be read by the host ribosomes

Answer 9

mRNA and there are 7 genome types and classes which is the basis for the Baltimore classification

Question 10

[Formation of viral mRNA] Virus classed on sense (+/-) depending on genomic RNA. What is the pos and neg sense?

Answer 10

1) Positive sense: viral genome is homologous to viral mRNA
2) Negative sense: viral genome is complementary to viral mRNA

Question 11

Most known viral genomes are what?

Answer 11

RNA

Question 12

What do viruses use to replicate their RNA genomes with?

Answer 12

RNA-dependent RNA polymerase (RdRp)

Pre-made

Question 13

RNA virus genomes

Answer 13

• RNA viruses encode their own viral RdRp as the cells they infect do not have the enzyme.
• Viral RdRp synthesises mRNA which is readable on host cell ribosomes

Question 14

Review of transcription

Answer 14

• mRNA is made from dsDNA, by RNA polymerase
• mRNA is processed in nucleus from a primary transcript, to the final mRNA:
• RNA is capped at 5’ end; poly(A) tail is added at 3’ end; intron splicing (eukaryotic)
• mRNA migrates from nucleus to cytoplasm
• Translation of mRNA and protein synthesis