virus 2

Question 1

attatchment

Answer 1

Virus binds to receptor on cell surface
(often protein, sometimes sugars, lipids,
or complexes of these)

Wide range of surface receptor used by wide variety of viruses

Same receptor used by different viruses; some viruses can use
more than one receptor

Question 2

attachment example HIV

Answer 2

Virus first binds to common,
low-affinity receptor

Virus then ‘rolls’ over cell
surface, until it binds to
high-affinity receptor

Binding with CD4 leaves virus too far from cell surface

Needs co-receptor (CCR5/CXCR4) to pull virus closer to cell
surface

Fusion between
virus envelope and
cell membrane

Question 3

penetration

Answer 3

Animal cells have mobile
lipid bilayer membrane:
relatively easy to cross

Non-enveloped animal viruses
enter via endocytosis

Enveloped animal viruses enter
via fusion

2nd uncoating step to release
nucleic acid

Question 4

penetration plant cells

Answer 4

Plant cells have rigid cell wall: much harder to cross

Viruses enter via damaged cell walls

Question 5

penetration bacterial cells

Answer 5

Bacterial cells have rigid cell wall: much harder to cross

tail fibres
1. bind and flex
2. tail pins bind
3. tail sheath contracts
4. tail core pushed through bacterial wall
4. nuc acid injected

Question 6

synthesis

Answer 6

Viruses need to produce proteins (for capsid itself and
for replication/synthesis)

to replicated nuc acid

use host cell macbinery (ribosomes, polymerase)

DNA- virus:
Host cell machinery set up to replicate DNA and produce
proteins from it

RNA- virus
RNA-dependent RNA-polymerase absent from host cell,
so need to synthesise it themselves

In some RNA-viruses, the genomic RNA itself can function
directly as mRNA; in others, mRNA needs to be transcribed
from the genomic RNA

Question 7

release

Answer 7

budding- host cell may survive
lysis- host cell destroyed

Question 8

HGT

Answer 8

Vertical gene transfer = transfer of genetic material from
parent to offspring

Viruses can become incorporated in host genome (8% of
human genome consists of endogenous retroviruses)

When coming out again, can take pieces of host genome with
them

When infecting another species, genetic material transferred
from one lineage to another

Question 9

sputnik

Answer 9

small virus infecting amoebae
can not infect on its own, only infect when infected by mamavirus

Question 10

polydnavirus

Answer 10

Insect virus, in parasitoid wasps

Virus normally incorporated in wasp genome, only reproduces
in wasp reproductive system, injected with eggs, enters host
blood cells, reduces host immune reaction