a2.3- viruses

Question 1

structural features common to viruses [8]

Answer 1

• non-living (no metabolic machinery of their own)
• small
• fixed size
• nucleic acid (DNA or RNA) as genetic material
• capsid made of protein
• no cytoplasm
• no/few enzymes
• relies on a host cell to replicate

Question 2

lytic cycle

Answer 2

1. attaches
   - binds to receptor that allows it to dock there
   - inject genetic material
2. makes copies of the virus
3. sm copies- cell membrane explodes
4. infect other organisms
   eg. bacteriophage lambda of E. Coli

Question 3

lysongenic cycle

Answer 3

1. attachment
2. entry of genetic material
3. integration
4. cell division
   - DNA becomes integrated into the bacterial DNA molecule
   - daughter cell continues the process
   - usually naked
   - temperate (wont try to kill the host yet)
   eg. bacteriophage lambda of E. Coli

Question 4

convergent evolution

Answer 4

• progressive hypothesis
• originated from simpler genetic elements
• gradually acquired the ability to infect and replicate within host cells

Question 5

evidence of covergent evolution

Answer 5

• matches how there are virus like components in some cells
  eg. retrotransposon/ circular plasmid is simple and can be synthesised

Question 6

divergent evolution

Answer 6

• regressive hypothesis
• originated from more complex cellular organisms that underwent a process of degeneration

Question 7

evidence for divergent evolution

Answer 7

• some viruses share genome similar to cellular organisms
• show variation in complexity and self-reliance

Question 8

reasons for rapid evolution [4]

Answer 8

• short generation time
• high mutation rates- often do not proofread
• increases rate of survival: evade defence mechanism of the host cell
• high natural selection pressure

Question 9

rapid evolution examples [2]

Answer 9

1. influenza
   - RNA replicase doesnt proofread + often makes errors
2. HIV
   - reverse transcriptase (rna -> dna) tricks us to use it

Question 10

antigenic drift

Answer 10

as more mutations occur- cant recognise the virus anymore

Question 11

antigenic shift

Answer 11

animal -> human

Question 12

consequences for treating diseases caused by rapidly evolving viruses

Answer 12

develop immunity to medicine- wont die

Question 13

what virus cant do the lysogenic cycle

Answer 13

T7 virus

Question 14

example of a small and simple virus

Answer 14

polio virus

Question 15

example of a large and complex virus

Answer 15

smallpox

Question 16

expectation for cells in bacteria

Answer 16

• to be self reliant
  EXCEPTION: parasitic bacteria, replicates inside a host cell

Question 17

diversity of structure in viruses [2]

Answer 17

1. diversity of genetic material
2. enveloped/ non-enveloped

Question 18

example of DNA virus [2]

Answer 18

1. smallpox
2. hepatitis B

Question 19

example of RNA virus [2]

Answer 19

1. corona virus
2. ebola disease