Lecture 1

Question 1

Why must viruses reach a balance in a population of hosts? What happens when this balance is disrupted?

Answer 1

Viruses must reach a balance in a population of hosts because if they kill the host 100% of the time, there will be no host left to persist in, and if the host population clears the virus completely, there will be no reservoir for the virus to persist.

When the balance is disrupted, it can lead to outbreaks or epidemics. Examples include SARS-CoV2, Ebola, SARS, avian influenza, etc.

Question 2

How can viruses impact host evolution?

Answer 2

Viruses can be driving forces in host evolution. They can act as selective forces in a population or provide direct or indirect advantages to host survival.

Question 3

Describe the relationship between the wasp Cotesia congregata and the virus it injects into its host, and the role of the virus in the wasp’s life cycle.

Answer 3

• a wasp that injects its eggs into a host worm along with a virus. The virus infects some of the worm’s immune cells, causing immunosuppression, which enables the wasp eggs to develop.
• the eggs used the nutrients from the worm to develop
• the genome for the virus is embedded into the wasp’s genome, and its expression is tissue-specific, with the cells that replicate this virus only found in the ovary of the female wasp. produced and kills the male embryos

Question 4

An obligatory step in the replication of retroviruses is the __________ of the _________ genome into the _________ genome

Answer 4

Integration of the virus genome into the host genome.

Question 5

What percentage of the human genome is comprised of human endogenous retroviruses (HERVs)?

Answer 5

Roughly 8%

Question 6

retroviruses have to convert their ____ genome into ____, and then this is integrated into the host cell genome before there is any transcription.

Answer 6

retroviruses have to convert their RNA genome into dsDNA, and then this is integrated into the host cell genome before there is any transcription.

Question 7

Describe the structure of a retrovirus

Answer 7

• capsid on inside
• genome packaged inside
• surrounding this is a lipid bilayer (envelope of glycoproteins embedded into it)
• can have spike proteins embedded in the bilayer (surface antigens) which are important as they mediate fusion

Question 8

What is important about spike proteins?

Answer 8

They mediate the fusion of the virus envelope with the cell envelope

Question 9

Where is there more biological diversity: within viruses or in all other bacterial, plant, and animal kingdoms combined?

Answer 9

Within viruses.

Question 10

Briefly describe the CRISPER-Cas9 genome editing system

Answer 10

• allows bacteria to recognize phage and if they’ve encountered it before they can destroy this virus
• can be used for many laboratory purposes, all you have to do is define the sequence of RNA

Question 11

Why are we not always sick?

Answer 11

Host defenses - physical and immunological (e.g. skin produces ribonucleases that protects the live cells under it from infection. also mucus, spit, secretions from stomach, etc)

Microbial specificity - proportionally few microbes are capable of infecting us. (because most viruses affect certain cell types, e.g. if the receptor matches a protein on the surface of the virus to replicate, if it CANT replicate CANT infect)

Inapparent infections - often we are infected but with no overt indications

Question 12

How are virus particles produced?

Answer 12

Virus particles are produced from the assembly of pre-formed components.

Question 13

Do virus particles (virions) grow or undergo division?

Answer 13

No, virus particles (virions) themselves do not grow or undergo division. This distinguishes them from other life forms.

Question 14

T or F: Viruses encode information for energy production, ribosomes, tRNAs and lipid membrane synthesis

Answer 14

FALSE: Viruses do NOT encode information for energy production, ribosomes, tRNAs (with a few exceptions), or lipid membrane synthesis.

Question 15

What are the five parts of the common strategy of viruses?

Answer 15

1. They build small particles to contain their nucleic acid genome.
2. They have small genomes: usually less than 100 genes; often less than 10.
3. They have an infectious cycle: particles bind to cells; enter; release genome; decode genome; replicate genome; build particles; exit cells.
4. They establish a relationship with their host (or hosts) ranging from benign to lethal.
5. They overcome host defenses with comparative ease

Question 16

Describe how viruses are visualized with use of technology.

Answer 16

Viruses are just below what you can see with a light microscope, very few you can actually see with it.

We can use red or green fluorescent proteins to locate them, fusing the proteins with the genes that include these and overall being able to see the light emitted by the particle.

Question 17

What is the capsid? (very general)

Answer 17

A structure that contains the viral genome

Question 18

What constraint affects the size of virus genomes?

Answer 18

Viruses have to be big, and can’t be so complex such that the genome has to be as well. Viruses often get around this by using a very few number of repeating proteins/components to build a large structure.

This is genetically an economical way of doing things to get the most out of that protein.

Question 19

Describe the use of embryonated chicken eggs as a host for viruses, and briefly describe the historical importance of this method.

Answer 19

You can poke a hole in the egg, and the Chorioallantoic membrane will sag away from the shell.

You can draw a little bit of virus (liquid) into the hole in the egg, cover it, and incubate it to let the viruses grow. Some viruses prefer different parts of the egg.

The majority of flu viruses were made by growing them in fertilized eggs before there were cell culture systems (dishes and other laboratory equipment).

Question 20

Describe microtubules, what they are, and what their function is.

Answer 20

Microtubules are tracks made up of tubulin and form tubes along which various cellular components move.

Viruses take advantage of microtubules for transport into cells.

Question 21

What motor protein is involved in transporting cargo along microtubules towards the nucleus?

Answer 21

The motor protein dynein links cargo (e.g., herpes capsid) to the microtubule and moves towards the nucleus, consuming ATP in the process.

Question 22

What motor protein moves cargo in the opposite direction (away from nucleus) along microtubules?

Answer 22

Kinesins move cargo in the opposite direction along microtubules.

Question 23

Why is regulating the activity of motor proteins important in viral transport?

Answer 23

It is important to regulate when to turn motor proteins on or off to ensure efficient viral transport. If viruses fail to reach the nucleus, they cannot produce more virus.

E.g. Herpes capsids can move along microtubules in the axon towards the cell body, facilitating viral infection and spread within the host.