Introduction to Virology (Schein) - 5/16/16

Question 1

Virus properties?

Answer 1

Small

Obligate intracellular parasites

Nucleic Acid + Protein

• More complex: +/- envelope
• All viruses have only one type of Nucleic Acid

Question 2

Basic structure of a virus?

Answer 2

Core
- Nucleic acid covered by a protein capsid (coat)

Envelope

• Lipid bilayer
• Host derived
• Glycoprotein spikes

Question 3

Properties of viruses used for classification? (8)

Answer 3

1. Nature of nucleic acid in genome
2. Genome size & organization: strategy of replication
3. Symmetry and structure of the nucleocapsid
4. Presence or absence of an envelope
5. Size and morphology of virus
6. (Sequence similarities of nucleic acids and proteins)
7. (Antigenic relationships)
8. (Biological properties, e.g. latency)

Question 4

1. Nature of DNA or RNA
2. Symmetry and structure of nucleocapsid?
3. Presence or absence of an envelope?

Answer 4

1.
- Single-stranded or double-stranded?
- ss RNA –> (+) or (-) stranded?
(+) strand = message sense (ribosomes can go right on it and start making protein)
(-) strand = need to be changed over to positive strand first

2.
Nucleocapsid icosohedral, helical, or complex?
Icosohedral capsid:
- Protomer - protein subunits
- Capsomere - made up of protomers
Helical capsid:
Complex symmetry:

Virion - naked or enveloped?
Glycoprotein spikes on outside of envelope attach onto receptors in host cell… similarly, vertices for naked viruses

Question 5

Steps in Virus Replication

Answer 5

1. Adsorption (glycoprotein spikes)
2. Entry
   a. Endocytic route: clathrin-mediated endocytosis and penetration
   b. Non-endocytic route: fusion at the cell surface
3. Synthesis of proteins which make the viral RNA or DNA (non-structural enzymatic proteins)
4. Replication of the genome (b/c millions of viruses are made per cell)
5. Synthesis of the structural proteins (so that virus can make new progeny that can go out and infect the world)
6. Packaging of the genome i.e. assembly of the nucleocapsid (so that new virus particles are assembled inside the cell…
7. In some cases, acquisition of an envelope (if there is an envelope, the envelope is added on…)
8. Release of virus from cell (…and the virus particles leave the cell)

Question 6

Effect of viruses on cells (4)

Answer 6

No apparent effect (infect cell and hang out latently)

Kill host cells (lysis)

Fuse infected cells (to form multinucleated giant cells - happens very often… usually in RNA viruses)

Transform cells

Question 7

Virus Detection?

Answer 7

Viral antigens (fluorescent antibodies against samples)

Serology (see if patient has antibodies against it) - want to check for 4x increase

PCR (doesn’t always work b/c you need a decent amount of sample for it to work)

Plaque assay (Circle - virus particle landed and killed… death multiplying)

Question 8

Hemagglutination?

Answer 8

Some virus particles can agglutinate RBC (attach to certain receptors on outside of RBC - form lattice and RBC pellets will not fall to bottom of test tube)

Question 9

Hemagglutination inhibition?

Answer 9

RBC + antiviral antibodies from serum + viruses –> viruses neutralized and hemagglutination inhibited