V2

Question 1

What are the steps of viral replication?

Answer 1

1. Recognition of a “target“ host cell.
2. Internalization of the virus.
3. Transcription and Replication.
4. Translation.
5. Post translational modification.
6. Release.
7. Particle maturation.

Question 2

What are the 3 types of viral internalisation?

Answer 2

• Fusion from without
• Receptor-mediated endocytosis
• Receptor-mediated endocytosis with fusion in the endosome

Question 3

Which viruses demonstrate “Fusion from without”

Answer 3

Measles, mumps, HIV, other membranous viruses

Question 4

Which viruses demonstrate “Receptor-mediated endocytosis”?

Answer 4

Naked viruses:
■ Adenovirus.
■ Picornaviruses [Polio, hepatitis A]
■ Rotavirus.

Question 5

Which viruses demonstrate “Receptor-mediated endocytosis with fusion in the endosome”?

Answer 5

Influenza, other membranous viruses

Question 6

What happens during transcription?

Answer 6

Formation of Viral mRNAs

Question 7

Describe transcription of RNA viruses

Answer 7

• Positive sense viral RNA used directly as viral
  mRNA.
• Negative sense viral RNA first transcribed to positive sense RNA

Question 8

Describe transcription of DNA viruses

Answer 8

mRNA is transcribed from initiation sites

Question 9

Describe transcription of Retroviruses

Answer 9

○ RNA → DNA.
○ Integrated (proviral DNA).
○ Viral mRNA transcribed from the proviral DNA.

Question 10

What is the end goal of translation?

Answer 10

Synthesis of Viral Proteins

Question 11

What happens during translation?

Answer 11

All viruses use cellular ribosomes to translate viral mRNAs, structural proteins and enzymes formed.
● Structural proteins: Building blocks of particles.
● Enzymes: Necessary for viral life cycle.

Question 12

What happens post-translation?

Answer 12

Modification of Viral Proteins

Question 13

Name 2 ways viral proteins are modified?

Answer 13

• 3D structure: Folding

- Glycosylation: Carbohydrate addition

Question 14

How are viruses released?

Answer 14

• Lytic viruses are released on lysis and death of the cell (poliovirus).
• Others (influenza, HIV, measles) escape by budding from the cell surface.

Question 15

Which viruses require a post-release maturation stage?

Answer 15

HIV and influenza

Question 16

What happens during the maturation stage?

Answer 16

• HIV proteins cleaved by viral protease.

- Influenza: cellular proteases are needed to cleave the viral HA spike protein.

Question 17

Name the mechanisms of genetic variation

Answer 17

• mutations
• gene reassortment
• recombination

Question 18

Define pathogenicity

Answer 18

Compares the severity of disease caused by different organisms

Question 19

Define virulence

Answer 19

Compares the severity of the disease caused by different strains of the same micro-organism

Question 20

What effects do viruses have on host cells?

Answer 20

• direct
• indirect
• cytoplasmic

Question 20

What direct effects do viruses have on host cells?

Answer 20

Some viruses kill cells they infect:

• Normal cellular metabolism comes to a halt.
• Cell becomes a virus factory.
• Some cells only release viruses when they disintegrate.

Question 21

What indirect effects do viruses have on host cells?

Answer 21

• Virus infected cells produce interferon
• Interferon results in an ‘antiviral state’ BUT this also interferes with normal cell function.
• The immune system attacks and destroys viral infected cells, final result is cell lysis or apoptosis

Question 22

What 2 things do cytopathic effects impact?

Answer 22

morphology and growth properties

Question 23

What is the cytopathic effect on morphology?

Answer 23

• Cell fusion (synctia)

- Inclusion bodies: Intracytoplasmic [predominantly RNA viruses], Intranuclear [predominanlty DNA viruses]

Question 24

What is the cytopathic effect on growth properties?

Answer 24

Transformation - Cells become immortalised [Epstein Barr virus]