viral infections

Question 1

types of DNA viruses

Answer 1

ds
gapped
ss
linear, circular

Question 2

types of RNA viruses

Answer 2

○ Ss
		○ Ds
		○ +ve sense and -ve sense
		○ Single piece (non-segmented)
Multiple pieces (segmented)

Question 3

virion

Answer 3

• Infectious particle
  
  • Carriers of nucleic acid payload
  • Extracellular phase o life cycle (spore)
    No replication/metabolism

Question 4

Infected cell

Answer 4

• ‘Living’ virus must be inside host cell

Dependent on cellular elements

Question 5

viruses use

Answer 5

- Phage therapy
		○ Lysis of bacteria
	- Reverse transcriptase
		○ Can generate cDNA from RNA
	- Oncolytic virotherapy
		○ Virus target/replicate in tumour cells
	- Viral gene therapy
		○ Research
	- Teachers
		○ Every solution tells us about the host
Understanding molecular biology

Question 6

Virus cycle

Answer 6

• Eclipse period
  ○ No new virus present in cells
  
  • Burst
    ○ Large number of new viruses produced per infected cell
  • Extracellular inert particle
    ○ Enter cell components dissociate
    ○ Protein components made, genome replicated
    Virions self-assemble from newly synthesised components

Question 7

spherical form

Answer 7

• Icosahedral ordered symmetry
  
  • Repeating units of protein
  • Polyhedron

Question 8

helical form

Answer 8

• Rod shaped coat
  
  • Repeating copies of protein coated on genome
    Hollow tube

Question 9

complex form

Answer 9

• Large viruses, non consistent symmetry

Question 10

5 basic steps of viral infection

Answer 10

1. Attachment
		○ Enter host organism
		○ Recognise specific target cell/tissue
	2. Penetration
		○ Releasing of genomic payload
	3. Gene expression/replication
		○ Synthesis of virion components
	4. Assembly of virions
		○ Self-assembly of structural subunits; packaging of nucleic acid
	5. Release of virions
Budding, lysis

Question 11

Transcription

Answer 11

nucleic acid genome –> mRNA
a. Must be able to make mRNA from genome
b. mRNA seen by cell - translation
Protein used for genome replication

Question 12

Replication

Answer 12

genome –> genome

New genome using viral genome as template

Question 13

Baltimore scheme based on:

Answer 13

1. Nature of genome nucleic acid

Mechanisms to generate mRNA

Question 14

Class 1 dsDNA virus

Answer 14

1. Binds to surface receptor
   
   2. DNA enters cell
      a. Replicate in nucleus
   3. Viral protein delivered to nucleus stimulate cellular DNA-dependent RNA polymerase to transcribe mRNA
   4. Protein stimulate Early genes
      a. Viral DNA-dependent DNA polymerase
      Late genes –> structural proteins

Question 15

Replication involves step-wise gene expression

Answer 15

• Immediate early (IE) –>
  
  • Early ( E) –>
    Late –> assembly and egress

Question 16

RNA class IV, class 5

Answer 16

• RNA –> mRNA –> protein (transcription)
  
  • gRNA –> anti-gRNA template –> gRNA (replication)
  • RNA-dependent RNA polymerase (RdRP)
  • +ve ssRNA = mRNA
    ○ Translated directly by the cell (ribosomes)
  • -ve ssRNA = antisense mRNA - cannot be translated
    ○ Needs to be converted to mRNA
    ○ Must carry RdRP with genome
  • -ve ssRNA, but not +ve ssRNA must carry RdRP
    Both must encode RdRP

Question 17

RNA class 6

Answer 17

• • ss RNA = mRNA
    
    • Converted to dsDNA (RNA –> DNA, Reverse transcriptase (RT))
      Inserted into genome

Question 18

Egress

Answer 18

• Enveloped
  ○ Budding - keep host cell intact
  
  • Naked
    Lysis

Question 19

Lytic cycle (lytic and temp phage)

Answer 19

• Phage injects dna
  
  • Replicates, lyses host cell
    Releases progeny

Question 20

Lysogenic (temp phage) latent

Answer 20

• Phage injects dna
  
  • Integrates into host cell chromosome (no replication)
  • Phage DNA (prophage) is then with the host chromosome
  • Genotoxic stress
    Reactivates, re-enters lytic cycle

Question 21

Transcriptional switches - repressors

Answer 21

• Left operon - lysogenic genes
  
  • Right operon - lytic genes
    To undergo cycle they repress the opposite promoter