Viruses

Question 1

capsid

Answer 1

• protein coat
• protects DNA/RNA from outside environment

Question 2

virus genetic morphology

Answer 2

• some use DNA, some RNA
• can be single stranded or double stranded
• single stranded can either be positive/coding (genetic information in same direction as transcription) or negative/anticoding

Question 3

viruses on bacteria

Answer 3

causes a ‘plaque’ on mats of bacteria such as E.coli which is a dead zone of bacteria

Question 4

smallpox, Columbian exchange

Answer 4

• airborne dsDNA virus indigenous to Europe
• colonisation gave Amerindian population smallpox, >90% died as they were less resistant
• downfall of Inca and Aztec empires
• biological warfare including General Amhurst giving infected blankets (1763)

Question 5

smallpox, variolation

Answer 5

• Edward Jenner 1796, cowpox vaccination
• variolation in Turkey recorded in early 1700s, insertion of smallpox scab on back
• also seen in other areas e.g. Pembrokeshire

Question 6

yellow fever

Answer 6

• related to Dengue and Zika
• originated in Africa, Europeans more susceptible
• spread by slave trade
• mosquito vector, Aedes spp.
• 15% mortality in Africa, little vaccine access

Question 7

HIV

Answer 7

• 1983
• no vaccine
• antiretroviral drugs reduce transmission and halt progression to AIDs

Question 8

advantage of single stranded genetic material

Answer 8

• no strand to use as a template to damage breaks and mutations
• ssRNA viruses such as influenza mutates more rapidly

Question 9

structure of viruses

Answer 9

• nucleocapsid = capsid and nucleic acid
• capsid made up of capsomers, a small number of structural proteins
• some viruses have a nuclear envelope, usually derived from cell membrane of host

Question 10

helical capsids

Answer 10

• simplest form of capsid
• capsomers self assemble around RNA to make a spiral tube

Question 11

virus penetration in bacteria

Answer 11

1. attachment
2. penetration and uncoating (genome injected directly into host)
3. expression and replication (genes get transcribed, structural and non-structural proteins formed)
4. assembly
   5, maturation
5. release/lysis of ~300 phage particles

Question 12

lysis vs lysogeny

Answer 12

• lytic phages kill host cell
• temperate/lysogenic phages can enter dormancy in host DNA (prophage), most genes are repressed

Question 13

bacteria and bacteriophages in nature

Answer 13

• viruses control bacterial numbers in aquatic systems
• infections change population dynamics of oligotrophic bacteria important in carbon cycle

Question 14

CRISPR-Cas9

Answer 14

• bacterial defence against phages
• Clustered Regularly Interspaced Short Palindromic repeats (LTRS either end like transposons)
• array of DNA sequences that are characteristic of particular viruses that have infected cell or ancestors before
• used in molecular biology for gene editing

Question 15

CRISPR-Cas9 defence

Answer 15

1. phage enters cell and is detected
2. cell consults CRISPR array
3. if part of nucleic acid of virus matched with library the cell can generate a defence response and the bacteria is protected against the phage

Question 16

phage therapy

Answer 16

• phages are very specific to bacteria unlike antibiotics
• effective way of treating bacterial infections if an exact strain is determined and a phage can be matched

Question 17

prions

Answer 17

• proteinaceous infectious particle
• transfers information through protein sequences
• scrapie (sheep)
• BSE (cows)
• LJP, FFI (humans)