Week 2&3 Questions

Question 1

MCQ1: How do virus attachment proteins find receptors to attach onto?

Answer 1

• Sensing receptors are near by
• Colliding with cells via Brownian Motion

Question 2

T/F Question 1: Receptors for dengue virus in host cells include heparan sulfate molecules.

Answer 2

True - present in almost all cells

Question 3

T/F Question 2: A mode of virus entry into the host cell that is shared between enveloped and non-enveloped viruses is fusion at the cell membrane.

Answer 3

False - only enveloped viruses sometimes use diffusion

Question 4

MCMO 1: Which of the following are necessary for dengue virus entry via endocytosis to occur successfully?
a) Fusion at the host cell membrane between virus and cell
b) Uncoating of the capsid
c) Formation of an endosome
d) Lowering of the pH in the endosome

Answer 4

c) Formation of an endosome
d) Lowering of the pH in the endosome

Question 5

MCQ 2: For an enveloped virus that undergoes membrane fusion, the envelope is:
a) Brought into the endosome
b) Left behind in the cytoplasm
c) Left outside the cell
d) Travels to the nucleus if the virus is a DNA virus
e) Destroyed in the cytoplasm by host enzymes

Answer 5

c) Left outside the cell

Question 6

Complete the sentence: Capsid softening occurs when acidification of the endosome triggers ____ leading to ____________________

Answer 6

Due to the lowering of the pressure inside, conformational changes occur allowing the release of the nucleic acid.

Question 7

SAQ 1: The entire lifecycle of most RNA viruses takes place in the host cell cytoplasm. However, Influenza has one key difference. Explain what this.

Answer 7

It replicates in the nucleus.
Does this because of genetic re-assortment (when two viruses can meet and become a new one)

Question 8

T/F Question 3: DNA viruses always need to bring along their own replicative enzymes otherwise their lifecycle cannot be completed.

Answer 8

False - Most DNA viruses use the hosts cell’s DNA polymerase

Question 9

SAQ 2: The Baltimore scheme of virus classification has one type of virus genome and replication strategy missing. What is it?

Answer 9

No negative sense single stranded DNA virus.
- Doesn’t exist as DNA can only replicate in one direction

Question 10

MCQ 3: Cytomegalovirus (CMV) belongs to which class of viruses in the Baltimore scheme?
a) Class III
b) Class IV
c) Class V
d) Class VII
e) Class I

Answer 10

Class I (dsDNA)
CMV = type of Herpesvirus
Varicella-Zoster Virus (VZV) = Herpesvirus

Question 11

What baltimore class is Herpesvirus?

Answer 11

Class I - Double Stranded DNA (dsDNA)

Question 12

What baltimore class is SARS-CoV-2

Answer 12

Class IV - Single Stranded RNA genome

Question 13

Name the Baltimore Classifications? (Hint there are 7)

Answer 13

Class I - dsDNA
Class II - ssDNAn
Class III - dsRNA
Class IV - ssRNA +
Class V - ssRNA -
Class VI - ssRNA - RT
Class VII - dsRNA -RT

Question 14

What Baltimore classification is HIV?

Answer 14

Class VI (ssRNA +)

Question 15

MCQ 4: Which class of viruses is most similar to how transcription, replication and translation occur in animal cells (Eukaryotes)?
a) Class III
b) Class IV
c) Class V
d) Class VII
e) Class I

Answer 15

Class I (dsDNA)
As double stranded and undergoes similair replicate

Question 16

In the Baltimore classification, what class is parvovirus?

Answer 16

Class II (sdDNA)

Question 17

SAQ 3: Human papilloma virus (HPV) is a DNA virus that is known to cause tumours. Which Baltimore class does it belong to? What key event occurs during infection with this virus compared to other viruses in its Baltimore class? How does it promote tumour formation?

Answer 17

Class I virus
- Integrates into the genome (changing it)
- Transcription of the genes, upregulates viral oncogenes (viral proteins) to upregulate cell signaling cascades.

Question 18

SAQ5: What do parvoviruses (Class II in the Baltimore scheme) need to do first in order for translation to occur and why?

Answer 18

Needs to transcribe the minus strand, for the RNA to translate into a viral protein.

Anti-genome needs to form DNA intermediate (a temporary double stranded DNA used for mRNA)

For understanding
- Parvoviruses start with a single-stranded DNA genome.
- They need to convert this into double-stranded DNA because cells can only make mRNA from double-stranded DNA.
- The cell uses one strand of this double-stranded DNA (intermediated DNA) to make mRNA.
-The mRNA is then used by the cell to make the viral proteins.

Question 19

SAQ 6: What key feature is different between class VII (Hepatitis B) and Class I viruses?

Answer 19

(Be able to draw diagram for exam)
- Class IIV is reverse transcription, this RNA gets encapsulated (as RNA isn’t naturally in the cytoplasm)
- Has an intermediated RNA
- Class I can be transcribed straight into mRNA

Question 20

MCMO 2: Which of the class/ classes of viruses below do NOT need to bring along in their virions the RNA dependent RNA polymerase (RdRp or RNA replicase)?
a) Class I
b) Class III
c) Class IV
d) Class V
e) Class VI

Answer 20

Class IV, VI

Explanation:
RdRp - only refers to RNA (not DNA)
+ RNA can use hosts (therefore they don’t carry)

Question 21

MCQ 5: Why is the Rotavirus genome never completely uncoated from its capsid?
a) It is needed for maturation of new viral particles
b) It protects the single stranded RNA genome
c) It protects the double stranded RNA genome
d) It catalyses the formation of new capsids

Answer 21

(Note: Rotavirus is class VI ssRNA - RT)
c.) It protects the double stranded RNA gecnome
- Prevent damage and protection

• RNA is more chemically reactive (capsulate it)

Question 22

SAQ 7: What is special about Class 4 viruses such as dengue?

Answer 22

Class IV (ssRNA plus sense)
- translated directly into protein
- positive sense acts as template mRNA
- Makes an entire polyprotein or two poly-proteins (cut up by protease)

Question 23

MCQ 5: How many polyproteins are translated in Ross River virus?
a) One
b) Two
c) Three
d) Four
e) Nine

Answer 23

(Class VI)
b.) two

Question 24

T/F: In SARS-CoV-2, the structural proteins are translated at the same time as the non-structural proteins directly off the genome which acts as a mRNA.

Answer 24

False:
Step 1: enters host cell, makes polyprotein using non-structural proteins.
Step 2: Synthesis then use of structural proteins.

Question 25

MCMO 3: Which of the following viruses belong to Class V?
a) HIV
b) Zika virus
c) Australian bat lyssavirus
d) Influenza
e) Respiratory Syncytial Virus (RSV)

Answer 25

Influenza and Rabies

Question 26

SAQ 8: What is special about the influenza genome that allows it to reassort?

Answer 26

• Can undergo genetic re-assortment
  (Combined with another virus can form a new one- new strain)
• allowed by segmented genome (8 - segments)

Question 27

SAQ 9: The HIV virion has two positive strands of RNA as its genome. Is the viral genome transcribed as an mRNA? Which 2 key steps have to occur before new viral proteins and viral genomes can be made?

Answer 27

Class VI
Has 2 single strands of RNA
- have to RT to DNA intermediate then mRNA

• Has to be integrated to the host genome before it can produce viral mRNA