Introduction To Virology

Question 1

What is virus

Answer 1

A virus is a non-cellular particle made up of genetic material and protein that can invade living cells

• genetic element that cannot replicate independently of a living ( host) cell

Question 2

What is virology

Answer 2

The study of viruses

Question 3

What is virus particle?

Answer 3

Extracellular form of a virus; allows virus to exist outside host and facilitates transmission from one host cell to another

Question 4

What is virion?

Answer 4

The infectious virus particle; the nucleic acid genome surrounded by a protein coat and, in some cases, other layers of material

Question 5

General properties of viruses

Answer 5

1. Viruses are obligate intracellular parasites of bacteria, fungi, protozoa, algae, plants n animals
2. Ultramicroscopic size : 20nm up to 450 nm (diameter)
3. Viral genomes may be RNA or DNA but not both
4. Viruses cannot make energy or proteins independently of a host cell
5. Viruses have a naked capsid or an envelope morphology
6. Viral components are assembled and do not replicate by division
7. Multiple by taking control of host cell’s genetic material and regulating the synthesis and assembly of new viruses.
8. Viral genomes are divided into two
   - DNA viruses - ssDNA / dsDNA
   - RNA viruses - ssRNA / dsDNA

Question 6

Taxonomy of viruses
How virus classified?
Examples

Answer 6

Classified on the basis of the hosts they infect

Ex:
Bacterial viruses (bacteriophages)
Animal viruses
Plant viruses

Question 7

What r the viral structures

Answer 7

Capsid

Capsomer

Question 8

What is capsid and its description?

Answer 8

Capsid = the protein shell that surrounds the genome of a virus particle
Description: composed of a number of protein molecules arranged in a precise and highly repetitive pattern around the nucleic acid

Question 9

What is capsomer and its description

Answer 9

Capsomer = subunit of the capsid

Description: smallest morphological unit visible with an electron microscope

Question 10

What is nucleocapsid

Answer 10

Complete complex of nucleic acid and protein packaged in the virion

Question 11

What is enveloped virus

Answer 11

Virus that contains additional layers around the nucleocapsid

Question 12

How does naked capsid virus formed

Answer 12

DNA or RNA + capsid protein + nucleocapsid = naked capsid virus

Nucleocapsid + lipid membrane, glycoproteins = enveloped virus

Question 13

Naked capsid virus vs envelope virus

Answer 13

Naked capsid virus:

• composed of nucleic acid
• stable to acid, temperature, drying
• retain infectivity even dry
• survive in adverse condition of gut
• antibody may be efficient for immunoprotection

Envelope protein:

• composed of lipids, proteins and glycoproteins
• easily disrupted by drying, acid, detergent
• must stay wet
• not survive in GIT
• need antibody and cell mediated immune response for protection

Question 14

Function and types of capsid

Answer 14

Function is to enclose and protect the nucleic acid

2 types

• helical
• icosahedral

Question 15

6 steps in phage replication

Answer 15

1. Absorption- binding of virus to specific molecule on host cell
2. Penetration - genome enters host cell
3. Replication- viral components produced
4. Assembly- viral components assembled
5. Maturation - completion of viral formation
6. Release - viruses leave cell to infect other cells

Question 16

What are the two methods of replication? N its description

Answer 16

Lytic cycle - the virus enters the cell, replicates itself hundreds of times, and then bursts out of the cell, destroying

Lysogenic cycle - the virus DNA integrates with the host DNA and the host’s cell helps create more virus DNA. An environmental change may cause the virus to enter the Lytic Cycle