virus genomes

Question 1

what must virus genomes contain?

Answer 1

information which can be recognised and decoded by the cell

Question 2

describe the genome of parvovirus?

Answer 2

linear, non-segmented, single stranded DNA genome of about 5kb. generally conserved and contain mostly functional sequences
genome forms hairpin structure due to palindromic sequences at the end

Question 3

what is a segmented genome?

Answer 3

a genome divided into two or more physically separate molecules of nucleic acid, all of which are packaged into a single virus particle

Question 4

what is a multipartite virus genome?

Answer 4

each genome segment is packaged into a separate virus particle

Question 5

what are the four unique features of a retrovirus genome?

Answer 5

1) they are the only viruses which are truly diploid
2) they are the only virus who’s genome is produced by cellular transcriptional machinery
3) they are the only virus whose genome requires a specific cellular RNA for replication
4) they are the only positive sense RNA genomes whose genome does not serve directly as mRNA

Question 6

what are retrovirus long terminal repeats?

Answer 6

identical sequences of DNA that repeat hundreds or thousands of times, found at either the end of retrotransposons or proviral DNA formed by reverse transcription of retroviral RNA

Question 7

what are retrovirus LTRs used for?

Answer 7

insertion of their genetic material into host genome

Question 8

which three theories explain the origin of viruses?

Answer 8

regressive evolution, cellular origins, independent entities

Question 9

what is a class I genome?

Answer 9

double stranded DNA viruses where replication is exclusively nuclear or replication occurs in the cytoplasm

Question 10

what is a class II genome?

Answer 10

single stranded DNA - replication occurs in the nucleus and involves the formation of a double stranded intermediate that serves as a template for the synthesis of single stranded progeny RNA

Question 11

what is a class III genome?

Answer 11

double stranded RNA virus with a segmented genome. each is transcribed separately to produce individual monocistronic mRNA

Question 12

what is a class IV genome?

Answer 12

single stranded +ve sense RNA - viruses with polycistronic mRNA which is translated into a poly protein and cleaved OR viruses with complex transcription that require two rounds of translation

Question 13

what is a class V genome?

Answer 13

single stranded - sense RNA. non segmented genomes where the transcription of the - sense genome by virion dependent RNA polymerase produces monocistronic mRNAs

Question 14

what is a class VI genome?

Answer 14

single stranded + sense RNA with a DNA intermediate

Question 15

what is a class VII genome?

Answer 15

double stranded DNA with RNA intermediate

Question 16

what things can be different in a virus genome?

Answer 16

• composition of the genome
• size and number of segments
• nucleotide sequence
• terminal structures
• coding capacity (open reading frames)
• regulatory sequences

Question 17

Give an example of a virus with a small DNA genome. outline its structure

Answer 17

parvovirus e.g. B19

• linear, non-segmented, single stranded genome
• generally conserved
• genome forms a hairpin structure

Question 18

what type of virus is SV40?

Answer 18

polyomavirus, small, double stranded DNA virus

Question 19

what type of virus are adenoviruses?

Answer 19

viruses with large, linear DNA genomes. express all genes co-ordinately to improve efficiency

Question 20

what type of virus are herpesviruses?

Answer 20

large, linear, double stranded DNA viruses

Question 21

what type of virus are poxviruses?

Answer 21

large, linear, double stranded DNA viruses. are more complex than herpes viruses and are almost independent of cellular mechanisms

Question 22

what is a ‘segmented’ virus genome?

Answer 22

where the genome is divided into two or more physically separate molecules of nucleic acid, inside a single virus particle

Question 23

what is a ‘multipartite’ virus genome?

Answer 23

where each segment of the genome is separated into a different virus particle

Question 24

what are the 4 unique features of retrovirus genomes?

Answer 24

1- they are the only viruses which are truly diploid
2- they are the only viruses whose genomes are produced by cellular transcriptional machinery without a virus encoded polymerase
3- they are the only viruses whose genomes require a specific cellular RNA for replication
4- they are the only positive sense RNA viruses whose genomes do not serve directly as mRNA

Question 25

what are retrovirus long terminal repeats?

Answer 25

identical sequences of DNA that repeat hundreds or thousands of times at either end of retrotransposons or proviral DNA formed by reverse transcription of retroviral RNA

Question 26

what is the purpose of retrovirus long terminal repeats?

Answer 26

they are used by viruses to insert their genetic material into the host genomes

Question 27

how are retrovirus long terminal repeats used?

Answer 27

• the LTRs are partially transcribed into an RNA intermediate
• reverse transcription into cDNA
• transcription into dsDNA
• mediation of integration of retroviral DNA by integrase

Question 28

why is retrovirus integration important?

Answer 28

• allows the virus to be replicated with the host genome
• stabilises the viral DNA
• aids efficient transcription of viral DNA into new copies of viral genome