14: Viruses - What are They?

Question 1

viruses outnumber cellular life

Answer 1

comprise the greatest biodiversity on earth
- for every living organism, more viruses than that
- viruses infect all types of life forms

viruses as major players in carbon/oxygen cycles that regulate the atmosphere
- bacteria die and material is reused so carbon coming from bacteria is redistributed/reused

Question 2

viruses’ history of coevolution

Answer 2

viruses as the first forms that existed on earth
- coevolving with viruses as long as we existed as mammals and as a life form

human genome as 8% virus
- integrated into our genomes in reproductive cells so theysyare transmitted

genome recognises viruses and thinks they might be useful
- some viral proteins to help fuse membranes

Question 3

synctin 1

Answer 3

without this protein, no reproduction/pregnancy and human life

spike protein recognises receptors on the membrane, fuses with the membrane and allows viral genome to be released into host cell

Question 4

tobacco mosaic disease

Answer 4

1886
- realised viruses existed less than 150 years ago

1891
- agent capable of permeating porcelain chamberland filters (which bacteria could never do)
- indication that agent was able to reproduce in some extracts, which is the idea of where viruses come from

Question 5

tobacco mosaic virus

Answer 5

first virus to be visualised in 1935 by wendell stanley with long filaments

Question 6

virus definition

Answer 6

infectious, obligate parasite comprising genetic material (DNA/RNA) surrounded by a protein coat and/or an envelope derived by a host cell membrane

all essentially have genetic material inside protective structures
- within genetic material, they need to have enough genes and a strategy so when the genome material is delivered to cells, it can takeover and transform

Question 7

virus as an organism with two phases

Answer 7

virion as a form found outside of cells
- protects DNA/RNA genomes of viruses

infected cell when it enters the cells

Question 8

difference between two forms of the virus

Answer 8

completely different

virion doesn’t replicate but that’s how it’s transmitted

in the infected cell, it replicates and manipulates/transforms the infected cell which now pumps virions out

Question 9

stages of a viral infection

Answer 9

attachment (to receptors to enter the cell)
penetration (fusing with the host to deliver genetic material inside the cell)
uncoating (for replication/transmission)
replication (creation of new proteins)
assembly
release

Question 10

characteristics of virus genomes

Answer 10

small genomes (tend to be 100x smaller than bacteria)

have 1Mx less genetic information than genomes of most plants/animals they infect

small units are easier to make so faster/better for replication/amplification

Question 11

key characteristic of viruses

Answer 11

high mutation rates which is important for higher genetic variability
- mutates efficiently so it can evolve
- many different possibilities and you only need one possibility that can grow

human response only targets one virus but you are already making new viruses which evade immune responses

Question 12

model of error catastrophe

Answer 12

if a virus doesn’t mutate, it’s stuck in one place
- age of catastrophe where viruses mutate as much as they can without dying

if we make viruses mutate more, you push the entire population to mutate to an extent that the population can’t survive

Question 13

red queen hypothesis

Answer 13

viruses mutate a lot but still stay in the same place because the host is also mutating/evolving
- every advantage a virus can have is counterbalanced by strategies the host develops to counteract new developed strategies

competition back and forth between the virus and host

Question 14

what do viruses have to do with only a bit of genetic information?

Answer 14

take over cellular machinery and redirect it to mass produce viral proteins, replicate genomes, etc.

avoid eradication by the immune system

keep the infected cell alive long enough to complete the replication cycle

Question 15

virions as obligate molecular parasites

Answer 15

we an use viruses to understand the host better
- study our biology by studying viruses

tumour suppressors

proto-oncogenes

DNA replication

gene expression
- simplification of machinery so we can understand as a model how our own genes are expressed

vaccines

splicing

gene therapy

CRISPR

Question 16

are all viruses bad?

Answer 16

can be beneficial for humans and not all are detrimental

bacteriophages shape gut microbial composition
- essential role of microbes and viruses that make these microbes

herpesviruses provide protection against listeria infection
- immune system more alert after being infected so we can resist external challenges better