Lecture 19

Question 1

Be able to label a diagram showing the parts of a typical virus

Answer 1

Genome: nucleic acid
Capsid: protects genome
Nucleocapsid: genome + capsid
Spikes: proteins mediate attachment

Question 2

Know what a plaque assay is and how the assay is conducted

Answer 2

Grow cells in a culture and add virus, look for lysed cells

Question 3

Describe groups of the Baltimore classification system for viruses

Answer 3

I. uses RNA or DNA
2. ss or ds
3. segmented or one molecule (nucleic acids)
4. nucleic acid replication intermediates

Question 4

Describe shapes of virus particles

Answer 4

Helical (spring)
Isosahedral (spherical)
Complex (funny)

Question 5

Describe viruses based on lipid envelope

Answer 5

Naked: no lipid envelope
Enveloped: phospholipid bilayer

Question 6

What is the effect of a viral envelope on survival during decontamination procedures

Answer 6

can get rid of with soap

Question 7

What are the steps involved in the viral replication cycle

Answer 7

1. Adsorption (attachement)
2. Internalization (penetration)
3. Nucleic acid liberation (nucleocapsid uncoating)
4. Synthesis (genome and protein)
5. Assembly (maturation)
6. Release

Question 8

What is the difference between viral entry by membrane fusion and by endocytosis?

Answer 8

Membrane fusion - envelope (membrane) fuses with cell membrane
Endocytosis- naked virus triggers receptors on host to make a vesicle

Question 9

What is the difference between viral exit by budding or exocytosis?

Answer 9

Budding - spike proteins push against membrane
Exocytosis - naked virus in vesicle

Question 10

What is the unusual nature of retroviral infections by cycles, such as HIV

Answer 10

they have an enzyme called reverse transcriptase which makes DNA from RNA, later becomes integrated into host chromosome

Question 11

What are the courses of viral disease?

Answer 11

Acute - brief
Latent - comes back briefly
Chronic - never goes away
Slow - almost goes away (HIV)

Question 12

How do viruses transform host cells?

Answer 12

1. disrupts tumor suprresor gene
2. activates oncogene

Question 13

What are three mechanisms by which viral infection can eventually kill the host cell?

Answer 13

1. cells are transformed into tumor cells
2. cells are lysed
   3.

Question 14

What is the process of genetic reassortment in segmented viruses?

Answer 14

segmented nucleic acids of different viruses will mix together in a host cell

Question 15

What is the advantage of the virus carrying out genetic reassortment

Answer 15

can have genetic reassortment in any host they infect, become more pathogenic

Question 16

What are three characteristics of plant viruses

Answer 16

1. enter through wounds
2. spread to adjacent cells via plasmodesmata
3. plants do not recover

Question 17

What are common symptoms of plant viral infections?

Answer 17

1. variegation
2. stunting of growth
3. tumor formation

Question 18

How do prions cause encephalopathic diseases?

Answer 18

misfolded proteins that cause others to misfold