Virology

Question 1

What is tissue tropism?

Answer 1

The tissues that viruses can be found in

Question 2

Summarise how viruses replicate

Answer 2

Some viruses replicate in the lungs and are transmitted in the air by breathing, coughing and sneezing.

Some viruses replicate in tissues required for pro-creation and are transmitted by sexual intercourse.

Some viruses replicate in cells of the immune system, preventing immune function.

Some viruses choose not to replicate immediately and cannot be detected by the immune system

Question 3

What is a virus?

Answer 3

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 4

What are prions?

Answer 4

proteins which do not contain nucleic acid and replicate inside the cell.

Question 5

Essential features for virus replication

Answer 5

• Entry into the cell - attachment/entry receptors – direct fusion or endocytosis.
• Genome movement within the cell - intracellular structures.
• Genome replication
• Genome packaging into protein shells – “Packaging” sequences in viral DNA or RNA.
• Exit from the cell – budding or lysis

Question 6

Summarise the different types of viral genomes

Answer 6

• Single-stranded RNA (ssRNA)
• Double-stranded RNA (dsRNA)
• Single-stranded DNA (ssDNA)
• Double-stranded RNA (dsDNA)

Question 7

What can RNA genomes be?

Answer 7

linear and segmented i.e. more than one RNA per capsid

Question 8

What is reverse transcription?

Answer 8

• o Takes information from the RNA state to the DNA state which can follow the dogma to make proteins

2. • - (-) sense RNA is converted into (+) sense RNA by RNA polymerase and this RNA can then be translated into proteins

Question 9

What is the The Baltimore Classification?

Answer 9

breakdown our understanding of how viruses are classed or grouped

Question 10

Summarise the different classes of virus according to the Baltimore

Answer 10

I. Double-stranded DNA viruses
II. Single-stranded (+) sense DNA viruses
III. Double-stranded RNA viruses
IV. Single-stranded (+) sense RNA viruses Togaviruses, etc)
V. Single-stranded (-) sense RNA viruses

VI. Single-stranded (+) sense RNA viruses with DNA intermediate in life-cycle
VII. Double-stranded DNA viruses with RNA intermediate

Question 11

What doe viruses with DNA and RNA genomes produce?

Answer 11

• Viruses with DNA genomes produce DNA polymerases

* Viruses with RNA genomes produce RNA polymerases

Question 12

What are viral proteins?

Answer 12

Proteins that form the capsid into which nucleic acid is packaged
- Proteins interact with one another in protein-protein interactions

Question 13

How does cancer arise as a result of viral pathogenesis?(2)

Answer 13

• Some viruses produce proteins that ensure the cell continually goes through the cell cycle

the cell produces factors that a virus might need. An example of this is the production of nucleotides that can be used by viral polymerases to make new viral genomes.

Question 14

Viruses that cause cancer - oncogenic…

Answer 14

• Human papilloma viruses (HPVs) – Papilloma virus, circular dsDNA genome, skin cancer
• Epstein-Barr virus (EBV) – Herpes virus, linear dsDNA genome, lymphoma
• Hepatitis B virus (HBV) – Hepadnavirus, circular dsDNA genome, carcinoma
• Hepatitis C virus (HCV) – Flavivirus, ssRNA genome, carcinoma
• Human herpes virus 8 (HHV-8) - Herpes virus, linear dsDNA genome, lymphoma
• Human T-lymphotrophic virus-1 (HTLV-1) – Retrovirus, RNA-DNA genome, leukemia/ lymphoma
• Merkel cell polyomavirus (MCV) – Polyomavirus, dsDNA genome, carcinoma

Question 15

What doe HPV do?

Answer 15

Human Papillomavirus (HPV) proteins E6 and E7 “remove the brakes” of the cell cycle

Question 16

What are E7 and E7?(3)

Answer 16

o Have direct and indirect effects on the cell cycle
o E7 binds directly to RB which affects proteins in the cell cycle such as E2F
o E6 influences p53 which is the master regulator of the cell cycle which in turn regulates p21 and cyclin A function etc.

Question 17

How do viruses cause immunodeficiency?(3)

Answer 17

some viruses replicate in the immune cells whose function is to recognize and kill infected cells.
• Replication in immune cells hides the virus from immune cells and inhibits immune cell function.
• Inhibition of immune cell function allows other pathogens to replicate in virus infected hosts and, thus, disease occurs.

Question 18

Summarise some HIV associated pathogens

Answer 18

• Virus: Kaposi’s sarcoma herpesvirus (KSHV), Herpes simplex virus (HSV)
• Bacteria, Mycobacterium tuberculosis, Salmonella
• Fungus Candida, Cryptococcus neoformans
• Parasite, Cryptosporidium, Toxoplasma gondii

Question 19

Give some examples of virus structure

Answer 19

1. spherical/icosahedral protein coat eg adenovirus
2. protein subunits around a nucleic acid strand eg TMV
3. complex protein coat eg bacteriophage

Question 20

Describe mechanism of HIV in T helper cells

Answer 20

1. glycoproteins called gp 120 located on virus surface bind to CD4 receptors on the surface of the T helper
2. envelope around virus fuses with T helper membrane
3. RNA enter cell
4. virus uses an enzyme called reverse transcriptase to reverse normal transcription and manufacture DNA from the RNA template
5. Integrase enzyme integrates HIV DNA into the host’s DNA
6. It can be transcribed and translated to produce virus proteins