W12 Essentials of Virology - I

Question 1

Virus

Answer 1

An infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host

Question 2

How many viruses are there?

Answer 2

possible that over 320,000 different viruses infect mammals

Question 3

Viruses can be found in different hosts

Answer 3

Humans
Animals (including insects)
Plants
Bacteria

some viruses can move between hosts

Question 4

Potential host range and transmission cycle strategies

Answer 4

Reservoir or amplifying hosts → virus → vectors → virus (by reintroduction of virus)

Vectors also → venereal transmission + vertical transmission (or horizontal)

Question 5

Tissue tropism

Answer 5

The tissues that viruses can be found in can be referred to as their “tissue tropism”

Question 6

Favouring of transmission

Answer 6

Through processes of evolution viruses evolve to replicate in tissues that favor transmission of between hosts and allow them to evade the immune system of the host

Question 7

Virus can cause a disease …

Answer 7

Viruses cause a range of disease, either directly or indirectly.

Viruses cause disease directly as a product of their host range and tissue tropism.

Viruses can cause disease indirectly by promoting or inhibiting cell function.

In humans the range of disease caused by viruses is very wide;

Cancer
Immunodeficiency
Respiratory

Disease can acute or chronic

Question 8

Bacteria

Answer 8

contain nucleic acid (DNA) covered in protein,
have a cell wall (a coat of sugar molecules) and
can replicate outside of the cell

Question 9

Prions

Answer 9

Prions are proteins, do not contain nucleic acid and replicate inside the cell

Question 10

Viruses (obligate…)

Answer 10

are nucleic acid (DNA or RNA) covered by proteins, have no cell wall and may or may not have a lipid coat. Viruses must replicate in the cell; they are “obligate cellular parasites”

Question 11

What are the essential structural features of a virus?

Answer 11

Different viruses have different structures, but retain similar organization.

Virus structure can be dictate host range and tissue tropism

Question 12

Essential features of virus replication

Answer 12

Entry into the cell - attachment/entry receptors – direct fusion or endocytosis.

Genome movement within the cell - intracellular structures.

Genome replication - see next lecture.

Genome packaging into protein shells – “Packaging” sequences in viral DNA or RNA.

Exit from the cell – budding or lysis

Question 13

Virus replication

Answer 13

Entry into cell + uncoating of DNA

Viral DNA replicated + transcribed

Capsid proteins formed w/viral DNA

Self assembly of new virus particles + their exit from cell