Viruses

Question 1

virus

Answer 1

• obligate intracellular parasite
• cannot replicate outside of host
• Structure
  
  • Nucleic acid core
  • Capsid
  • envelope
  • Pre-formed enzymes

Question 2

Nucleic acid core

Answer 2

RNA or DNA (double stranded or single stranded)

Function: carries genes necessary for virus to take over host

Question 3

Capsid

Answer 3

Protein coat made up of capsomers subunits

function: protection and attachment

Question 4

Envelope

Answer 4

Membrane surrounding capsid of some animal viruses

function: protection and attachment via spikes

Question 5

Pre-formed enzymes

Answer 5

May be present to assist take-over

examples:

• DNA or RNA polymerase
• replicases: copy RNA
• Reverse transcriptase: synthesis of DNA from RNA

Question 6

Virus Shapes:

Answer 6

Helical: rod or thread like
Ex: rabies virus, ebola virus

Polyhedral: spherically shaped
ex: polio virus

Complex: structurally complex
ex: T-even bacteriophage

Question 7

Cultivation of viruses

Answer 7

Require living cells

Methods:

1. living animals
   - virus injects into susceptible animal
2. embryonate eggs
   - virus injected into fertilized egg
3. cell cultures

Question 8

Cell culture

Answer 8

Types:

1. primary cell lines: a few generations in vitro
2. embryonic diploid cell lines: ~100 generations in vitro
3. immortal cell lines: can be maintained indefinitely
   ex. HeLa cells (henrietta lacks-1951)

Question 9

Bacteriophage/phage

Answer 9

virus that infects bacteria

Question 10

Cultivation of bacteriophage

Answer 10

1. plate lawn of bacterial culture
2. add bacteriophage
3. plaques form

Question 11

Bacteriophage replication

Answer 11

Lytic: host cell dies
lysogenic: host cell remains alive

Question 12

lytic cycle

Answer 12

1. attachment:
   - tail fibers attach to receptors on bacteria
2. Penetration
   - Lysozymes released to degrade cell wall
   - cell wall punctured
   - DNA transferred into host
3. Biosynthesis
   - host machinery produce new viral structures
4. Maturation
   - new viral structures are assembled
5. release
   - Lysozyme lyses cekk –> release new viruses

Question 13

Lysogenic cycle

Answer 13

1. attachment
2. penetration
3. dna forms a circle
4. circle recombines with circular DNA of bacteria
   - -> prophage
5. every time host replicates, virus genome is replicated as well
6. can remain like this for a long period of time (latency)
7. virus can break out of prophage and switch to lytic (induction/excision)

Question 14

Results of Lysogeny

Answer 14

1. immunity to reinfection by same phage
2. phage conversion: host exhibits new properties
3. specialized transduction: when induced out of cycle may take part of host genome

Question 15

Animal Virus Multiplication

Answer 15

1. Attachment: virus attaches to host using spikes or capsid
2. Penetration: enters by receptor mediated endocytosis or fusion
3. uncoating: enzymatic removal of capsid
4. Biosynthesis: host machinery produce new viral structures
5. maturation: new viral structures are assembled
6. release: budding (enveloped), host lysis (naked)

Question 16

Latent Viral infections

Answer 16

virus remains in asymptomatic in host cell
Reactivated by:
-fever, UV light, stress, trauma, hormonal changes, etc

Question 17

viruses and cancer

Answer 17

Protooncogenes:

• usually encode proteins involved in cell cycle regulation
• can be mutated to become oncogenes

Oncogenes:
-genes that can cause a normal cell to be transformed into a malignant cell

Viruses:

• mutate protooncogenes
• introduce oncogenes to different hosts