Diversity of viruses

Question 1

Phage MS2

Answer 1

Small icosahedral +ve strand RNA virus
Encodes only 4 proteins
Maximises coding region by having OVERLAPPING genes

Question 2

Phage lambdaX174

Answer 2

Small circular single stranded DNA virus
Icosahedral virion
The first DNA to be sequenced (1977 Fred Sanger)

Question 3

Filamentous bacteriophage

Answer 3

M13
Released without lysing the bacterial cell in a BUDDING process
M13 has been used extensively for cloning and sequencing

Question 4

Bacteriophage with double stranded DNA genomes

Answer 4

These are virulent and temperate bacteriophage

• Virulent bacteriophage kill their hosts after infection (e.g. T4)
• Temperate viruses can replicate together with host cells and dont always kill them (e.g. lambda phage)

Question 5

Phage T4: A virulent bacteriophage

Answer 5

T4 has double stranded DNA genome

Question 6

Lambda: a temperate bacteriophage

Answer 6

Can undergo a LYTIC cycle where it kills infected cells
Can also undergo a LYSOGENIC cycle - most virus genes are not expressed, sometimes the virus genome integrates into the host cell genome

Question 7

Consequences of being infected by a temperate bacteriophage

Answer 7

Lysogenic pathway –> Repressor protein expressed – immunity to incoming phage
Lytic pathway –>
Cell lysis

Question 8

Bacteriophage as antibiotics

Answer 8

Phage therapy

Question 9

Viruses of Archaea

Answer 9

Only DNA viruses have been found thus far to infect archaea
Similar in structure to bacteriophage - infect Euryarchaeota
Most diverse group are those that infect the hyperthermophiles (Crenarchaeota)

Question 10

Plant Viruses

Answer 10

Most are +ve strand RNA viruses
Small genomes
Travel cell to cell through the plasmodermata
E.g. mimiviruses, chorella viruses -DNA, tobacco mosaic virus, tomato spot wilt virus -RNA

Question 11

Tobacco mosaic virus TMV

Answer 11

+ve rod shaped RNA virus
infects tobacco plants and tomato plants
Replication is similar to MS2 phage

Question 12

TMV Replication

Answer 12

TMV enters plants through damaged cell walls
Replication takes place in the cytoplasm
Large genome encodes only 4 proteins

Question 13

Animal viruses -RNA

Answer 13

Cause common diseases of animals

• e.g. foot and mouth disease virus
• e.g. blue tongue virus (vector=midges)

Question 14

Poliovirus

Answer 14

• Replication in cytoplasm
• Genome acts as the mRNA: it can be translated directly
• Replication is compartmentalised
• Simple capsid/RNA genome assembly process

Question 15

Picornaviruses

Answer 15

+ve single strand animal RNA viruses

Question 16

RNA virus divergence

Answer 16

• Need replicase to replicate their genomes
• The virus encodes the enzyme RNA-dependent RNA polymerase (replicase)
• This copies RNA into RNA but makes lots of errors
• This leads to VIRUS DIVERGENCE

Question 17

Segmented genomes:Drift and shift

Answer 17

• 2 different ‘flu viruses enter respiratory epithelial cells
• Genome segments can be swapped inside the cells
• Reassortment Progeny
• A novel flu virus emerges

Question 18

-VE strand RNA viruses

Answer 18

Influenza -avian, swine, human
New pandemics can arise
Birds = reservoirs hosts
Pigs= mixing vessels
Reassortment in pigs leads to antigenic shift
Adaptation in pigs leads to antigenic drift