Virology: Chapter 1

Question 1

What is the definition of a virus?

Answer 1

independent nucleic acid genome that replicate inside a host cell by hijacking host’s biosynthetic machinery to propagate and project itself onto new host cells

Question 2

What is the difference between a cell and a virus? (3 points)

Answer 2

a virus:
1. simple structure, acellular; lack organelles and plasma membrane
2. genetic information is encoded by DNA / RNA
3. depends on a living cell to self-replicate

Question 3

What is the central dogma of biology and how do viruses not follow that dogma?

Answer 3

DNA transcribed to mRNA, mRNA translated to proteins by ribosomes

RNA viruses and Retroviruses don’t follow that rule because they both don’t have a DNA phase in their replication cycle

RNA virus: replicate and transcribe their RNA genome
Retrovirus: reverse transcribe their RNA genome back to DNA

Question 4

What are the two forms / states of a virus

Answer 4

Extraceullar form and Intracellular state

Question 5

Explain a virus’ extracellular form

Answer 5

it’s the virus particle (virion) that binds to virus receptors and transfers genome to the host cell to replicate

Question 6

What do genes do? (3 points)

Answer 6

1. allows viral genome replication
2. production of viral structure proteins
3. production of enzymes for replication (if they can’t get these enzymes from the host cell)

Question 7

Genome is covered by a protective capsid, what is a capsid? what is a capsomere

Answer 7

Capsid is a protein shell that protects the viral genome, it’s made out of multiple capsomeres.

Capsomeres are individual protein subunit

Question 8

Explain the 3 types of capsids

Answer 8

1. Helical capsid
   - elongated tubular structure
   - as long as the genome
2. Icosahedral capsid
   - symmetrical = max interval volume
   - equilateral triangles (20)
   - can be naked or enveloped
3. Complex capsid
   - not helical / symmetrical
   - form complex structures made of multiple protein layers

Question 9

What are the functions of the capsid in a NAKED Virus

Answer 9

1. protect viral genome
2. help virus survive outside the host
3. assist with host cell entry
4. determines the virus shape

Question 10

What is an enveloped virus?

Answer 10

A virus that is enveloped by a lipid bilayer/nucleic/golgi which is stolen by host cell

Question 11

What does the envelope virus contain

Answer 11

viral proteins to help infect new cell

Question 12

What is a naked virus?

Answer 12

virus with no envelope, only capsid surround the genome

Question 13

Why is the envelope virus less stable?

Answer 13

Because the lipid bilayer is fragile and can be damaged by heat, drying, detergent, pH change
This fragility causes decrease in virality

Naked viruses are just protein shells that are more stable in the environment so they survive better

Question 14

What is anti-microbial therapy?

Answer 14

uses bacteriophages to treat patients with bacterial infections = ointments, enemas, mouthwash

Question 15

What is Gene therapy?

Answer 15

uses viruses to deliver a wild type copy of a gene to a cell that is carrying a mutated copy of a gene
- deliver crispr/cas systems to a cell

Question 16

Treatment of cancers through viruses

Answer 16

viruses can be genetically modified to be used as anti-cancer agents
= virus replicates permissive cancer cells not healthy cells

Question 17

All new strains viruses evolve from

Answer 17

pre-existing viruses

Question 18

small pox:
HIV:
H1N1:
Sars-cov-2:

Answer 18

Poxvirus (rodents)
SIV (virus that infects non human)
bird / swine flu virus
bats

Question 19

What are the two pathways of virus evolution? and explain

Answer 19

Co-evolution with host
+healthy host cell = healthy virus
- host cell extinct = virus extinct
=ebola

Infection of multiple host species
+ if host cell is comprimised, virus can thrive and replicate
- but it cannot optimize because the virus is constantly mutating
= influenza, rabies

Question 20

Example of co-evolution: rabbits and myxoma virus

Answer 20

when the virus first spread, it killed most of the rabbits, however they started to become resilient towards it and the virulence decreases, so the population increased
co evolution: the virus and the host evolved in response to each other

Question 21

Bad mutation means

Answer 21

the virus decreases in virulence, less effective infection and can’t produce more virus

Question 22

Neutral mutation means

Answer 22

no effect

Question 23

Beneficial mutation means

Answer 23

benefits the virus where the virus gains ability to infect the host cell, and increase in virulence

Question 24

What is the trade off in beneficial mutation

Answer 24

if the virus kills the host cell too soon due to increase in virulence, the virus will be exposed when the host cell dies, and the immune system will kill it

Question 25

Enveloped viruses are typically less robust or stable than naked viruses when outside of the host cell. Suggest reasons as to why this might be so.

Answer 25

Because the lipid bilayer is fragile because there are no covalent bonds holding the lipids together this makes them highly susceptible to dehydration or other disruptions the lipid layers often contain proteins that the virus uses as an anti- receptor to bind to the host cell and the lipids themselves are often required for entry into the cell via fusion of the viral envelope to the host cell membrane

Question 26

What are some of the functions of the protein coat that surrounds the genome of a naked virus particle?

Answer 26

To transport the genome from host cell to host cell, to protect the genome from environmental agents that could damage the genome (e.g., UV light, proteases, molecules that could oxidize the nucleic acid) and to facilitate binding to susceptible host cells

Question 27

DNA virus mutation rate is (less than) or (more than) RNA virus And what does that mean?

Answer 27

Less than It means that RNA virus has more variation and diversity, making it LESS stable DNA virus is MORE stable because it doesn't mutate as much