Virus

Question 1

What do viruses need to replicate?

Answer 1

Host cell

Question 2

Viral genome

Answer 2

Complete set of genetic material.
DNA or RNA, never both.
Single stranded OR double stranded.

Question 3

Viral capsid

Answer 3

Protein shell/coat surrounding and protecting genome (DNA/RNA).

Composed of smaller protein subunits called capsomeres.

Question 4

Viral envelope

Answer 4

Bilayer of lipids and glycoproteins surrounding some viruses.

Protects genetic material and facilitates entry into host cells.

Question 5

What determines symmetry of a virus?

Answer 5

Arrangement of capsomeres

Question 6

Naked virus

Answer 6

Virus without envelope

Question 7

Size of viruses

Answer 7

10-100nm

Question 8

Obligate intracellular parasites

Answer 8

Can only multiply inside living host cell

Question 9

Viral nucleic acid

Answer 9

Contains genetic material DNA or RNA, never both.

Question 10

Nucleocapsid

Answer 10

Entire unit of nucleic acid surrounded by a capsid.

Question 11

Viral proteins

Answer 11

Building blocks and functional components of viruses.

Essential for replication and interaction with host cells.

Question 12

RNA virus

Answer 12

RNA genomes.

Much higher mutation rates than DNA viruses.

Question 13

DNA viruses

Answer 13

DNA genomes.

Generally more stable than RNA viruses.

Question 14

Icosahedral virus

Answer 14

Viruses with 20 equilateral triangle faces.

Surrounded by capsid.

Most stable.

Question 15

Filamentous virus

Answer 15

Linear, thin thread like appearance, rod-shaped viruses.

Surrounded by capsid.

Question 16

Head-tail virus

Answer 16

Hybrid.

Icosahedral head containing viral genome.

Flexible filamentous tail used to attach and infect host cells.

Surrounded by capsid.

Question 17

Lytic replication

Answer 17

Virus causes host cell death when released.

Question 18

Lysogenic replication

Answer 18

Virus integrates its genetic material into host cell and remains dormant.

Host cell continues to live and function normally.

Question 19

Viral persistence

Answer 19

Virus remains in specific cells of infected individual without clearance.

(HIV, Epstein-Barr, Hep B)

Question 20

Viral latency

Answer 20

Ability of pathogenic virus to lie dormant within a cell.

Type of persistent viral infection.

Lysogenic part of viral life cycle.

Question 21

Viral tropism

Answer 21

The ability of a virus to productively infect a particular cell, tissue or host species.

Question 22

Factors influencing viral tropism

Answer 22

Viral proteins - mediate virus entry by binding to specific receptors on cell and facilitating fusion.

Host receptors - viruses use to attach and enter cells.

Host-cell machinery - viruses utilises for replication, transcription and translation.

Immune response and cytokines.

Question 23

Virus eclipse phase

Answer 23

Period between infection/viral entry into host cell AND the production of new virions.

As short as 3 hours or as long as several months.

Question 24

Virus replication stages:

Answer 24

1. Adsorption/attachment
2. Penetration
3. Uncoating
4. Transcription
5. Synthesis of viral components
6. Assembly
7. Release

Question 25

1. Adsorption/attachment

Answer 25

Virus particle attaches to specific receptors on host cell.

Question 26

2. Penetration

Answer 26

Process by which the virus or its genome enter host cell. Can happen by: - Endocytosis - Fusion - Translocation

Question 27

3. Uncoating

Answer 27

After penetration there is a period when the virus cannot be detected. This eclipse phase begins uncoating lipid membrane and capsid. Releases viral nucleic acid and acts as template for mRNA.

Question 28

4. Transcription

Answer 28

mRNA code for synthesis of enzymes. Virus takes advantage of existing cell structures to replicate itself.

Question 29

5. Synthesis of viral components

Answer 29

Viral proteins (structural and non-structural enzymes) are synthesised and built on ribosomes.

Question 30

6. Assembly

Answer 30

Incorporates nucleic acid into capsomeres. Can occur in; host nucleus, cytoplasm or plasma membrane.

Question 31

7. Release

Answer 31

Release of new virions from host cell. Lytic - host cell dies once virus released. Lysogenic - host cell continues to live and function normally after viral genome is incorporated into host cell.

Question 32

HIV

Answer 32

Human immunodeficiency virus. Leads to compromised immune system and opportunistic infection. Targets specific T-lymphocytes (CD4) Icosahedral RNA

Question 33

Hepatitis B

Answer 33

Viral infection that attacks the liver. Spread through; blood, semen, and other bodily fluids. Acute or chronic. Icosahedral DNA

Question 34

Varicella Zoster

Answer 34

Chickenpox/shingles. Targets T-lymphocytes and epithelial cells. Remains latent within nervous system. Icosahedral DNA

Question 35

Herpes

Answer 35

HSV1 - Herpes Labialis. HSV2 - genital herpes. Remains dormant in body after initial infection. Spreads through; direct skin-to-skin contact, mucous membranes or breaks in skin. Icosahedral DNA

Question 36

Influenza

Answer 36

Acute respiratory disease. Spreads through; air in droplets. Head-tail or filamentous. RNA.