Lecture 7

Question 1

Structural Features

Answer 1

EM use only

A) Nucleic Acid Core

• DNA or RNA/ Single or double stranded
• One type of NA (DNA or RNA, never both)

B) Protein coat (capsid) = protein shell (capsomeres) surround core

C)Envelope surround the capsid in some cases

Question 2

Naked Virus

Answer 2

• NA core + capsid coat

- Protein spikes attached to capsid

Question 3

Enveloped Virus

Answer 3

• NA core + Capsid Coat + Lipid envelope around capsid

- Protein “spikes” attached to envelope

Question 4

Life Cycle of a virus

Answer 4

1. Adsorption -Attaches to host via spikes
2. Penetration / Uncoating - NA released from capsid
3. Gene Expression - Genes expressed to produce more NA and Proteins
4. Assembly - New Viruses
5. Release - Exit cell

Question 5

Host Range

Answer 5

Specific to each virus

Determined by Receptors on host
Machinery of host

Viruses classified by host

Question 6

1. Absorption

Answer 6

Virus spike attach to host

Step can be blocked

Question 7

2. Penetration / Uncoating

Answer 7

1. Receptor -mediated Endocytosis -> naked
   Vesicle / swallowed
2. Receptor Mediated fusion -> Enveloped viruses
   Lipid membrane merge

Host enzyme degrade capsid

Question 8

3. Gene Expression

Answer 8

NA is transcribed, translated, replicated

Dependent on host

Question 9

4. Assembly

Answer 9

Create new viruses

Either in cell nucleus or cytoplasm

Question 10

5. Release

Answer 10

Naked = Cell death lysis

envelope = cell membrane fusion, slow buds

Question 11

Viral Life cycle

Answer 11

1. Lytic acute infection (cell death)
2. Persistent (Chronic) infection = symptoms less severe, virus particles present, slow release
3. Latent infection = NA inserted into host cell Chromosome, replicates with host, not expressed

Can later on activate and call lysis

4. Oncogenic Infection = Cause cell to grow in an uncontrolled way

Question 12

Drugs that block Viral absorption or penetration

Answer 12

Selzentry = Bind to receptor protein

Docosanol (Abreva) = Fatty acid fuses with membrane

Question 13

Drugs that block uncoating of viral NA

Answer 13

Bind to capsid and prevent breakdown

Virus specific

Question 14

Drugs that block viral gene expression and replication (MOST COMMON ANTIVIRAL)

Answer 14

Viral Polymerase inhibitors = bind to DNA polymerase = no new DNA

Nucleic Acid Analogues = Block virus replication

Inactive form less toxic= Acyclovir = converted during infection

Question 15

Drugs that block viral assembly or release

Answer 15

Protease inhibitors = Protein creator

Neuraminidase inhibitors =Needed for release

Question 16

Interferon

Answer 16

Naturally produced anti-viral chemical

Question 17

Problems with Anti Viral Agents

Answer 17

1. Toxicity
2. Latent viruses
3. In effective if given after cycle has started
4. Resistance develops quickly
5. New agents difficult (animal models)