Viruses (Lec. 14)

Question 1

Define virion

Answer 1

A single infectious virus particle comprised of a capsid, a genome, and sometimes an envelope

Question 2

Define capsid

Answer 2

A capsid is composed of capsomeres and is a protein coat that provides shape and protection

Question 3

Define envelope

Answer 3

A lipoprotein layer derived from the host cell membrane that surrounds the capsid

Question 4

Define CPE

Answer 4

The cytopathic effect is the visible structural changes in a host cell’s morphology when it’s infected by a virus.

Question 5

Define TSE

Answer 5

Transmissible spongiform encephalopathies are prion diseases which are fatal and neurodegenerative (e.g. scrapie, mad cow disease, chronic wasting disease, kuru, and Creutzfeldt-Jakob disease).

Question 6

Explain why viruses are classified as nonliving microbes

Answer 6

They depend on a host for survival (obligate intracellular pathogens)

Question 7

Describe features and functions of spikes

Answer 7

Spikes are viral proteins that extend from the capsid and through the envelope. They provide host cell specificity (help with host cell attachment/entry).

Question 8

Described the generalized steps for bacteriophage replication

Answer 8

1. Attachment: the virion attaches to the host cell
2. Penetration: the viral DNA enters the host cell (the viroid’s protein coat remains outside)
3. Synthesis of viral nucleic acids and protein
4. Assembly and packaging of new viruses
5. Cell lysis and release of new virions

Question 9

Describe the steps for animal virus replication

Answer 9

1. Attachment: viral surface proteins interact with host plasma membrane proteins
2. Penetration occurs by fusion or endocytosis
3. Uncoating: genome is released from capsid
4. Replication: genome is replicated and viral proteins are made
5. Assembly: new virions are assembled
6. Release: virions are released by budding or lysis

Question 10

Compare and contrast structure and replication of enveloped and naked animal viruses

Answer 10

Enveloped viruses have an envelope and can enter a host cell through membrane fusion OR receptor-mediated endocytosis (naked viruses can only do the second one)

Question 11

Describe the 4 possible outcomes of animal virus infection

Answer 11

Virulent infection: lysis of host cell (most common)
Latent infection: viral genome exists in the host genome as a provirus and virions are not produced; host cell is unharmed until/unless virulent pathway is triggered.
Persistent infections: slow release of virions from host cell by budding does not result in cell lysis.
Transformation: conversion of normal cell into tumor cell

Question 12

Distinguish between + stranded and - stranded RNA viruses

Answer 12

Positive-stranded RNA viruses serve as both the mRNA and genomic material, and is translated into proteins by the host cell’s ribosomes. Negative-stranded RNA is used as a template to produce positive-stranded viral genomes, which can then be translated, replicated, or packaged.

Question 13

Identify 2 viral families that utilize reverse transcriptase

Answer 13

Retroviruses and hepadnaviruses

Question 14

Identify 2 viral families that cause tumors

Answer 14

Polyoma virus S V40 and Herpesviruses

Question 15

Describe lab methods for culturing and identifying viruses

Answer 15

Viruses cannot be seen with a light microscope, so plaque assays are used as well as observations of cytopathic effect. Immunologic methods (serology) and molecular methods (DNA sequencing or PCR or other stuff) are also used.

Question 16

Describe viroids and prions as infectious agents

Answer 16

Viroids are infectious RNA molecules that lack a protein component (naked RNA with no protein capsid) and are the smallest known pathogens. Prions are infectious proteins whose extracellular form contains only protein, no nucleic acid. They are known to cause disease in animals (no plant prion diseases discovered yet). The disease itself is caused when normal proteins in the body become abnormal and clump in the brain, which leads to brain damage and death.