*Microbiology 4 (lecture 7)

Question 1

Are viruses bigger or smaller than bacteria?

Answer 1

Smaller

Question 2

What are the parts of a virus? (4)

Answer 2

Nucleic acid
Protein coat (also known as capsid)
Envelope (lipid - only some viruses)
Protein spikes (only some viruses)

Question 3

Do viruses contain RNA or DNA?

Answer 3

Either RNA or DNA (never both)

Question 4

3 types of virus structure?

Answer 4

Icosahedral symmetry (made of 20 equilateral triangles) e.g. adenovirus
Helical symmetry (made up of a single repeated unit that aggregate around the viral nucleic acid)
Complex virus structure

Question 5

How do viruses infect a cell? (6)

Answer 5

• The virus attaches to a cell receptor via a ligand (protein spike)
• The virus enters the cell (either by endocytosis (if the virus doesn’t have an envelope) or by fusion of viral and cell envelope mediated by viral enzymes (if the virus has an envelope)
• Uncoating of the virus (viral nucleic acid is released from the capsid)
• Nucleic acid and protein synthesis (host ribosomes are always used and some viral enzymes are used to build new proteins and nucleic acid from instruction in the original nucleic acid)
• Assembly of assembling virus within cell
• release of newly formed virus (several different mechanisms)

Question 6

During the assembly stage what may be seen down the light microscope?

Answer 6

Crystals of assembling virus - inclusions

Question 7

Mechanisms by which newly formed viruses within a cell can be released?

Answer 7

Budding (part of the cell membrane is napped off to produce a virus with an envelope around it)
Lysis (virus accumulates until it causes lyses of the cell and release of virus)

Question 8

Is the host cell killed by budding?

Answer 8

No

Question 9

Is the host cell killed by release of virus via lysis?

Answer 9

Yes

Question 10

Why do antibiotics not work on viruses?

Answer 10

Antibiotics work by being selectively toxic to certain bacterial structures (e.g. ribosomes, cell wall) which viruses do not have

Question 11

What are the possible targets of antiviral drugs?

Answer 11

Viral nucleic acid polymerases
Other viral enzymes involved in viral nucleic acid replication or protein synthesis e.g. integers, protease
Uncoating
Attachement/ entry
release

Question 12

What is another type of therapy (apart from antiviral drugs) that can be used to treat viruses?

Answer 12

Immune adjuvants

Question 13

What is an example of an anti-flu antiviral?

Answer 13

Zanamivir

Question 14

How does a virus cause illness? (3)

Answer 14

Cell death due to lysis or hijacking of cell machinery
Cell death due to the immune system (especially cytotoxic T cells)
Cell proliferation (e.g. wart causing virus infects skin cells and causes them to proliferate - can lead to cancer)

Question 15

What type of cancer can hepatitis B and C viruses cause?

Answer 15

Primary hepatocellular carcinoma

Question 16

What type of cancer can Human herpes virus type 8 cause?

Answer 16

Kaposi’s sarcoma

Question 17

What type of cancer can helicobacter pylori cause?

Answer 17

Gastric cancer

Question 18

What type of leukocyte can recognise proteins on the cell surface as being foreign and will signal the infected cell to commit suicide to prevent the formation of further mature virus?

Answer 18

Cytotoxic T lymphocytes

Question 19

What can bind directly to viruses to prevent them binding to cellular receptors?

Answer 19

Antibodies e.g. IgG, IgM

Question 20

What makes you feel so unwell when you have influenza?

Answer 20

The virus induces interferon release which makes you feel ill

Question 21

What are interferons?

Answer 21

a group of signaling proteins made and released by host cells in response to the presence of several pathogens

Question 22

What can happen to viruses in terms of being eliminated from the body?

Answer 22

• Virus can be eliminated by the immune system
• Some viruses may become quiescent (latent) with the possibility of reactivating e.g. herpes simplex virus, varicella-zoster virus
• The virus may remain continually active for years causing chronic infection e.g. HIV and hep C (these patients may remain asymptomatic but infectious for decades before getting life threatening complications)

Question 23

How are virus infection confirmed in the laboratory?

Answer 23

Either by detection of the antibody response against the virus (antigen detection)
By detection of the presence of the virus itself (PCR)
(older techniques include cell culture and electron microscopy)

Question 24

what is the incubation period?

Answer 24

The period between exposure to an infection and development of symptoms

Question 25

Out of IgM and IgG, what never fully disappears from the blood stream after infection?

Answer 25

IgG

Question 26

How can recent infection be differentiated from past infection?

Answer 26

Detection of virus specific IgM antibodies Detection of rising titre of IgG antibodies Detection of very high titre of IgG antibodies (paired (acute and convalescent) blood samples maybe required)