25 - virus structure

Question 1

why study viruses?

Answer 1

they are a major cause of disease in man, animals and plants

responsable for lots of suffering, death and economic hardship

they can be exploited for our benefit

Question 2

HIV

Answer 2

best known virus

40 million living with it
2/3 live in sub-saraharan africa

vaccine development still a major challenge

Question 3

other bad viruses

Answer 3

• measles virus
• hepatitis B virus
• influenza virus
• human papilloma virus
• rabies
• ebola

Question 4

characteristics of viruses

Answer 4

are obligate intracellular parasites - can only grow in host cells

usually have a specific hose and maybe tissue

Question 5

what are virions?

Answer 5

purified virus particles

Question 6

structure of viruses

Answer 6

• can be single or double stranded
• can be linear or circular
• can have 1 or more strands of nucleic acids
• have a nuclear capsid
• need cells machinery

Question 7

whats the nuclear capsid around viruses?

Answer 7

surround by envelope and host cell membrane

displayed on the surface are highly glycosylated proteins - allows interaction with other host cells

sometimes have a layer of matrix protein

Question 8

how are viruses classified?

Answer 8

morphology - size and shape

biology - type of tissue infected

genome organisation and replication - Baltimore classification

Question 9

whats Baltimore classification?

Answer 9

looks at the different routes for synthesising RNA and relocating the viral genome

Question 10

what is DNA replicated by?

Answer 10

DNA polymerase

Question 11

what is DNA transcribed to RNA by?

Answer 11

RNA polymerase

Question 12

whats the template for DNA and RNA polymerase?

Answer 12

DNA

Question 13

what is RNA replicated by?

Answer 13

RNA dependent RNA polymerases

Question 14

what is RNA transcribed to DNA by?

Answer 14

RNA dependent DNA polymerases

= reverse transcriptase

Question 15

what are the different kinds of sub-viruses?

Answer 15

• satellite viruses
• virusoids
• viroids
• prions

Question 16

what are satellite viruses?

Answer 16

codes for its own structural proteins but cannot replicate in the host cell unless its co-infected with a helper virus which provides factors needed for replication of the satellites genome (disabled virus particles)

Question 17

what are virusoids?

Answer 17

the genome doesn’t code for structural proteins

its packaged using structural proteins coded for by a helper virus which is needed to co-infect the host cell

Question 18

what are viroids?

Answer 18

special type of infectious RNA which is not packaged in any protein or envelope - makes infectious RNA

Question 19

what are prions?

Answer 19

special type of infectious protein and lacks any nucleic acid molecules - no genome associated