Viruses

Question 1

Which viruses have ssRNA genomes?

Answer 1

Tobacco
Polio
Paramyxovirus
Flu?

Question 2

Which viruses have DsDNA genomes?

Answer 2

Herpes virus

Adenovirus

Question 3

Name a virus with helical symmetry

Answer 3

Rod viruses have helical symmetry
E.g. Tobacco virus
Length determined by length of RNA
Width determined by size and packing of subunits

Question 4

Describe the symmetry in bacteriophages

Answer 4

Complex virus- Composed of parts each with its own symmetry
Icosahedral head
Helical tail sheath
Tail fibres

Question 5

What do bacteriophages do?

Answer 5

Infect bacteria only

Carry lysozyme for cell entry- breaks PG in cell wall

Question 6

Name 2 viruses that have both RNA and DNA genomes

Answer 6

Retrovirus-RNA genome, DNA intermediate, reverse transcriptase used to convert RNA–> DNA e.g. HIV

Hepadnavirus- DNA genome with RNA intermediate e.g. Hepatitis b

Question 7

Name a virus with icosahedral symmetry and explain what is meant by this structure

Answer 7

Adenovirus
20 faces- most efficient packing in a closed shell
12 pentons
5-3-2 rotational symmetry

Question 8

What is a virus?

Answer 8

• V. small’ infectious obligate intracellular parasite
• cannot generate ATP
• are an assemblage of chemicals and cannot replicate
• replication is dependent upon infection of a cellular host
• no known virus contains ribosomes
• some have RNA genomes
• some have single stranded genomes of RNA and DNA
• cannot be seen by light microscope! Must be a electron microscope.