nature and structure of viruses

Question 1

Tobacco mosaic virus

Answer 1

• first filterable virus

- discovered by Dmitri Iwanoski

Question 2

Foot-and mouth-disease

Answer 2

• first filterable animal virus

- discovered by F. Loeffler and P. Frosch

Question 3

Yellow fever virus

Answer 3

• first human virus

- discovered by Walter Reed

Question 4

A. Negri

Answer 4

discovered inclusion bodies of rabies virus in 1903

Question 5

P. Rous

Answer 5

first demonstration of a solid tumor virus, Rous sarcoma virus (chicken cancer)

Question 6

Bacteriophages

Answer 6

-discovered by Twort and d’herelle

Question 7

A. Woodruff and E. Goodpasture

Answer 7

reported on the use of embryonated hen’s eggs as a host for viruses in 1931

Question 8

J. Enders

Answer 8

reported that nonneural tissue supports poliovirus replication in culture

Question 9

Knoll and Ruska

Answer 9

invented the electron microscope

Question 10

Virus

Answer 10

submicroscopic particles whose genomes are elements of nucleic acid that replicate inside living cells using the cellular synthetic machinery for the production of progeny virons.

Question 11

Host range

Answer 11

range of animal species and tissue cells that the virus can infect

Question 12

structural unit (sand)

Answer 12

protein subunit which may be assembled into capsomeres

Question 13

capsomeres (blocks)

Answer 13

Morphological subunits from which the virus capsid is built

Question 14

capsid

Answer 14

protein shell, or coat that encloses the nucleic acid genome

Question 15

envelops

Answer 15

a lipid-containing membrane that surrounds some viruses

Question 16

nucleocapsid

Answer 16

the capsid together with the enclosed nucleic acid

Question 17

virion

Answer 17

the complete infective virus particle

Question 18

incomplete virion

Answer 18

virion without nucleic acid (empty capsid)

Question 19

defective virus

Answer 19

a virus that cannot replicate because it lacks a full complement of viral genes

Question 20

pseudotype

Answer 20

during replication in co-infected cells, the genome of one virus may become encapsidated in the heterologous protein coat encoded by the second virus

Question 21

pseudovirion

Answer 21

during viral replication,the capsid sometimes encloses host nucleic acid rather than viral nucleic acid.

Question 22

episome

Answer 22

• autonomous extra-chromosomal genetic element (which may later become integrated into chromosomal DNA or remain separate)
• viral chromosome separate from host chromosome

Question 23

viral attachment proteins

Answer 23

capsid and envelope proteins that mediate that attachment of viruses to specific host cell receptors

Question 24

provirus

Answer 24

viral DNA that is integrated into a host cell chromosome in a latent state and must be activated before it is transcribed, leading to production of progeny virions

Question 25

Cubic symmetry (icosahedron)

Answer 25

• the most efficient arrangement for subunits in a closed shell
• solid with 12 corners (vertices), 20 equilateral triangular faces, and 30 edges

Question 26

penton

Answer 26

capsomeres located at the vertices of icosahedral virions; each is surrounded by five neighbors

Question 27

Helical symmetry

Answer 27

• the capsomeres and nucleic acid molecules self-assemble as a helix
• it is not possible for “empty” helical particles (incomplete virions) to form

Question 28

complex viruses

Answer 28

• some virus particles do not exhibit simple cubic or helical symmetry but are more complicated in structure
• poxvirus