Viral Infection

Question 1

Structure of viruses:

Answer 1

Contain DNA or RNA

Capsid (protein shell) made up of repeated subunits of virally encoded protein

Sometimes has a lipid envelope

Question 2

Icosahedral symmetry:

Answer 2

Virus consists of repeated subunits that make up equilateral triangles arranged in a symmetrical fashion

Question 3

Helical symmetry:

Answer 3

Virus made up of a single repeated unit

Question 4

Uncoating definition:

Answer 4

When viral nucleic acid is released from capsid

Question 5

Viral replication:

Answer 5

Virus uses host ribosomes to produce new viral proteins

Host polymerases may also be used (e.g. reverse transcriptase for HIV)

Question 6

What is budding?

Answer 6

Virus released with envelope derived from host cell membrane
Doesn’t kill cell

Question 7

What is lysis?

Answer 7

Virus accumulates until cell bursts, killing cell

Question 8

Viral replication summary:

Answer 8

1. Attachments of virus to host cell via specific receptors
2. Virus enters host cell via endocytosis
3. Uncoating of virus
4. New viral protein produced
5. Assembly of viral proteins and nucleic acids
6. Release of virus (via budding or lysis)

Question 9

Pathogenesis (3):

Answer 9

Cell death due to lysis
Cell death due to immune system
Cell proliferation due to cancer

Question 10

Role of Cytotoxic T Lymphocytes (CTLs) during viral infection:

Answer 10

Recognise foreign cell surface proteins
Signals to infected cell to commit suicide

Question 11

Neutralising antibodies role during viral infection and the 2 types:

Answer 11

Marks cell for destruction
IgG and IgM

Question 12

2 types of viral persistence:

Answer 12

Virus becomes quiescent and does not undergo active replication - virus can still reactivate after latency period

Virus remains continually active for years - this is a chronic infection