(LE4) Virology

Question 1

What are general characteristics of a virus?

Answer 1

• Acellular (can’t live alone)
• Obligate intracellular parasites

Question 2

What is the general structure of a virus?

Answer 2

Nucleic acid core
- single-stranded or double-stranded
- whole or segmented

Capsid
- protein coat

Some viruses have an envelope
- plasma membrane derived from host
- viral spikes

Question 3

What are the types of capsid shapes a virus can have?

Answer 3

1. polyhedron
2. Helical (tube)
3. complex
   - both
   - e.g. bacteriophage

All can have envelope

Question 4

What is the smallest known virus? Largest?

Answer 4

Polio: 30 nm

Ebola: 1 µm

Question 5

What are the two leading hypotheses for the origins of viruses?

Answer 5

1. Devolved cells adapting to parasitic lifestyle while losing the ability to replicate on their own
2. Self-replicating nucleic acids that evolved with cells

Question 6

How is viral taxonomy determined?

Answer 6

Based on type and arrangement of nucleic acids
- can be based on capsids, morphology, envelope, and size
- family names
- hard to differentiate genera and species

Question 7

What is a common characteristic of all Herpes viruses?

Answer 7

they all show latency

Question 8

How do you cultivate a virus in the lab?

Answer 8

Requires cell culture
- embryonated eggs
- live animal or plant hosts
- bacteria lawn

Question 9

What are plaques on a bacterial lawn?

Answer 9

Areas where virus has killed bacteria and spread

Question 10

What is a primary culture?

Answer 10

tissue/cells removed from the host organism
- Cons: kills host and is temporary

Question 11

What is an immortalized culture?

Answer 11

Derived from cancer cells -> indefinite growth
- e.g. HeLa cells

Question 12

What is a bacteriophage? Briefly describe its morphology

Answer 12

A virus that infects bacteria

Question 13

What type of lifecycle is performed by T-even phages? What are the steps?

Answer 13

Lytic lifecycle

Question 14

What distinct phase in Phage lambda’s lifecycle allows it to lay “dormant”? What happens in that phase?

Answer 14

Lysogenic phase

Question 15

What is a prophage?

Answer 15

Viral DNA incorporated into the bacterial chromosome

Question 16

What triggers prophage to enter the lytic cycle?

Answer 16

Induction event
- starvation, chemicals, UV light, etc.

Question 17

What is transduction?

Answer 17

horizontal gene transfer via a bacteriophage

Question 18

What is specialized transduction?

Answer 18

Viral DNA goes into a specific part of bacterial DNA and takes specific genes with it

Question 19

What is generalized transduction?

Answer 19

Viral DNA is randomly put into the chromosome and random bacterial DNA gets taken with it
- entire chromosome is broken apart when the phage is lytic
- recombination of bacterial DNA with the new genes

Question 20

What virulence factors can generalized transduction cause?

Answer 20

• Shiga toxin plasmid in E. coli
• antibiotic resistance

Question 21

What is the first step of the animal virus lifecycle?

Answer 21

Adsorption (attachment)
- specific cell type (receptor specificity)
- host specificity

Question 22

What is the second step of the animal virus lifecycle?

Answer 22

Penetration

Question 23

What is the third step of the animal virus lifecycle?

Answer 23

Uncoating
- release genome into cell
- destroy capsid and vesicle

Question 24

What is the fourth step of animal virus lifecycle?

Answer 24

Biosynthesis
- Replication -> make genome (host machinery)
- protein synthesis TXN, TSN
i. capsid proteins
ii. viral spikes

Question 25

What is the fifth step of animal virus lifecycle?

Answer 25

Assembly (maturation)

Question 26

What is the sixth step of animal virus lifecycle?

Answer 26

release: Lysis of host cell: non-enveloped viruses Budding: enveloped viruses - exocytosis -> taking host PM -> envelope

Question 27

What is one instance phage therapy is used for?

Answer 27

Diabetic ulcers - antibiotic resistance

Question 28

During adsorption, how do non-enveloped viruses attach compared to enveloped viruses?

Answer 28

Non-enveloped: capsid binds receptor Enveloped: viral spike binds receptor

Question 29

How do non-enveloped viruses penetrate compared to enveloped viruses?

Answer 29

Non-enveloped: adsorb then trigger endocytosis to enter host cell Enveloped: fuse the envelope to cell membrane to enter host cell. Viral envelope left on plasma membrane (recognized by T-cells)

Question 30

What virus can remain latent in neurons after uncoating?

Answer 30

herpesvirus family: HSV-1, HSV-2, VZV

Question 31

How do DNA viruses replicate?

Answer 31

Uses host cell machinery

Question 32

What are the 2 types of ssRNA viruses?

Answer 32

(+) sense strand - RNA can act like mRNA and be translated directly by host ribosome - has AUG codon 3'-AUG.....-5' (-) sense strand - template for mRNA, cannot be translated directly - Has UAC codon-> translated into AUG on mRNA 5'-UAC....-3'

Question 33

What enzymes are used by viruses for replication?

Answer 33

RNA-dependent RNA polymerase - Template: RNA - Product: RNA Reverse Transcriptase - Template: RNA - Product: DNA - Only known to be used by retroviruses e.g. HIV

Question 34

Describe viral replication for +ssRNA

Answer 34

Question 35

Describe viral replication for -ssRNA

Answer 35

Question 36

What virus causes Burkitt's lymphoma?

Answer 36

Epstein-Barr virus (EBV)

Question 37

What virus causes cervical cancer?

Answer 37

HPV-8 and HPV-16

Question 38

What virus causes liver cancer?

Answer 38

Hep B and Hep C

Question 39

What virus causes Kaposi's Sarcoma?

Answer 39

Human Herpes Virus (HHV-8) (with assistance from HIV)

Question 40

What virus causes T-cell leukemia/lymphoma?

Answer 40

Human T-cell Leukemia virus (HTLV-1)

Question 41

What factors allow viruses to cause cancer in the host?

Answer 41

Contains oncogenes (genes that have capacity to cause cancer) which are involved in cell growth cycle Provirus (HIV and HPV) incorporate viral genome into host cell chromosome disrupting tumor suppressing genes. e.g. contact inhibition genes

Question 42

What are prions?

Answer 42

proteinaceous infectious particles - misfolded proteins with ability to transmit misfolded shape onto normal variants of same protein - usually found in brain proteins - needs to be able to replicate itself to be infectious - can cause same misfolding in normal proteins

Question 43

Briefly describe Pruisner's research on Kuru

Answer 43

Filtered out all microbes and destroyed DNA/RNA viruses. Then, denatured proteins with urea and phenol and concluded it was a new protein-based pathogen