Mesnage - Virus structure and function

Question 1

Name 5 key features of a virus’s nucleic acid composition

Answer 1

1) DNA can be ds or ss
2) RNA can be ds or ss
3) usually between 2-20kb (only needs specific genes)
4) ds>ss and DNA>RNA
5) usually organised into 1 molecule that can be fragmented

Question 2

what is a viral capsid? describe its composition and structure

Answer 2

the capsid is the protein coat surrounding the virus

it is composed of 1+ proteins called capsomers and has a icosahedral or helical symmetry

Question 3

what is the composition and role of the envelope?

Answer 3

made up of lipid bilayer with glycoproteins either host or virus encoded
allows entry into host cell by fusion and endocytosis

Question 4

name a non-symmetrical virus

Answer 4

smallpox

Question 5

name a virus from each viral group and give their nucleic acid type

Answer 5

1 papillomavirus - dsDNA
2 adeno-associated virus - ssDNA
3 reovirus - dsRNA
4 foot and mouth disease - (+)ssRNA
5 influenza - (-)ssRNA
6 HIV/AIDS - (+)ssRNA (retrovirus)
7 Hep B - dsDNA

Question 6

describe the virulent (lytic) life cycle

Answer 6

attachment of virus to host cell
penetration of viral particle into host
phage DNA circularises 
phage DNA and proteins assembled into virons
cell lyses, releasing phage virions

Question 7

describe the temperate (lysogenic) life cycle

Answer 7

attachment of virus to host cell
penetration of viral particle into host
phage DNA circularises 
phage DNA integrates with bacterial chromosome by recombination (prophage) 
cell divides

Question 8

list the 5 stages of the general viral life cycle

Answer 8

1) attachment
2) genome injection
3) production of nucleic acids and proteins
4) maturation (assembly of viral particles)
5) release

Question 9

list the 5 stages of the DNA viral life cycle

Answer 9

1) virion attaches to host cell
2) uncovered DNA and virion enter cell
3) viral DNA enters nucleus
4) virions assemble
5) virions released

Question 10

list the 5 stages of the ssRNA(+) viral life cycle

Answer 10

1) virion attaches to host cell
2) uncovered RNA and virion enter cell
3) (-) strand synthesised from (+) for genome and (+) strand used to synthesise proteins
4) virions assemble
5) virions released

Question 11

list the 5 stages of the ssRNA(-) viral life cycle

Answer 11

1) virion attaches to host cell
2) uncovered RNA and virion enter cell
3) (+) strand synthesised from (-) and (+) strand used to synthesise proteins and (-) genome
4) virions assemble
5) virions released

Question 12

list the 5 stages of the dsRNA viral life cycle

Answer 12

1) virion attaches to host cell
2) uncovered RNA and virion enter cell
3) (+) strand synthesised from dsRNA, (+) strand used to synthesise proteins and (-) genome
4) virions assemble
5) virions released

Question 13

list the 7 stages of the retrovirus viral life cycle

Answer 13

1) virus enters cell via fusion between attachment spikes and the host cell receptors
2) Viral RNA genome and 3 viral enzymes are released
reverse transcriptase, integrase, protease
3) Reverse transcriptase copies viral RNA to dsDNA.
4) dsDNA is transported into the nucleus and integrated into host genome by viral integrase. The provirus can replicated when the host cell replicates.
5) Transcription of the provirus produces new genomes and RNA encoding capsid, enzymes, and envelope proteins.
6) Viral proteins are processed by viral proteases; some
go to the plasma membrane.
7) Mature retrovirus buds out of the host cell, acquiring an envelope and attachment spikes