Chapter 6

Question 1

Describe the general characteristics of viruses.

Answer 1

Viruses have several common characteristics: they are small, have DNA or RNA genomes, and are obligate intracellular parasites

Question 2

Describe viral genomes

Answer 2

A viral genome is composed of DNA or RNA and enclosed in a capsid, which is a protein coat covering the nucleic acid or genome. The viral genome can be single-stranded or double-stranded and linear or circular.

Question 3

What is a host range?

Answer 3

Host range describes the breadth of organisms a parasite is capable of infecting

Question 4

What are vectors? Differentiate between biological and mechanical vectors.

Answer 4

Biological vectors, such as mosquitoes and ticks may carry pathogens that can multiply within their bodies and be delivered to new hosts, usually by biting. Mechanical vectors, such as flies can pick up infectious agents on the outside of their bodies and transmit them through physical contact.

Question 5

What is phage therapy?

Answer 5

Phage therapy, viral phage therapy, or phago-therapy is the therapeutic use of bacteriophages for the treatment of pathogenic bacterial infections.

Question 6

Describe the general characteristics of viral life cycles

Answer 6

The virus life cycle could be divided into six steps: attachment, penetration, uncoating, gene expression and replication, assembly, and release

Question 7

Describe the lytic and lysogenic life cycles

Answer 7

The lytic cycle involves the reproduction of viruses using a host cell to manufacture more viruses; the viruses then burst out of the cell. The lysogenic cycle involves the incorporation of the viral genome into the host cell genome, infecting it from within.

Question 8

Describe the replication process of animal viruses

Answer 8

Their replication process begins when the virion delivers its genome to a cell. The viral genome encodes proteins required for the synthesis of new viral genomes. New viral proteins plus new viral genomes assemble to form new particles or virions, and so the cycle continues.

Question 9

Transduction

Answer 9

Occurs when a bacteriophage transfers bacterial DNA from one bacterium to another
during sequential infections

Question 10

Persistent infection

Answer 10

Occurs when a virus is not completely cleared from the system of the host but stays in certain tissues or organs of the infected person.

Question 11

Eclipse phase

Answer 11

Viruses bind and penetrate the cells with no virions detected in the medium

Question 12

Burst

Answer 12

The chief difference in the viral growth curve compared to a bacterial growth curve occurs when
virions are released from the lysed host cell at the same time

Question 13

Burst size

Answer 13

The number of virions per bacterium released

Question 14

Viral titer

Answer 14

The number of virions per unit volume

Question 15

What size filter pore is needed to collect a virus?

Answer 15

200 nanometers

Question 16

How are bacteriophages grown?

Answer 16

For bacteriophages, cultures are grown by infecting bacterial cells. The phage can then be isolated from the resulting plaques in a lawn of bacteria on a plate.

Question 17

What is a plaque?

Answer 17

A clear area on an otherwise opaque field of bacteria that indicates the inhibition or dissolution of the bacterial cells by some agent, either a virus or an antibiotic.

Question 18

How are animal viruses grown?

Answer 18

Unlike bacteria, many of which can be grown on an artificial nutrient medium, viruses require a living host cell for replication. Infected host cells (eukaryotic or prokaryotic) can be cultured and grown, and then the growth medium can be harvested as a source of virus.

Question 19

What are cytopathic effects (CPEs)?

Answer 19

The changes in cell morphology caused by infecting virus

Question 20

Describe prions and how they increase in number.

Answer 20

A prion is a type of protein that can trigger normal proteins in the brain to fold abnormally. They self-propagate through recruitment of their normally folded counterparts.

Question 21

What are viroids?

Answer 21

Viroids are small single-stranded, circular RNAs that are infectious pathogens. Unlike viruses, they have no protein coating