Chapter 13

Question 1

What is the most basic structural definition of a virus?

Answer 1

A virus is a tiny infectious particle composed of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid.

Question 2

What are the general characteristics of viruses?

Answer 2

• Viruses can only replicate inside host cells.
• They contain genetic material (DNA or RNA) but lack cellular structures.
• Viruses lack metabolic machinery and depend on host cell machinery for replication.
• They have a protein coat (capsid) that surrounds their genetic material.
• Some viruses have an additional lipid envelope derived from the host cell membrane

Question 3

What is a virion?

Answer 3

A virion is a complete, fully developed viral particle that is capable of infecting a host cell.

Question 4

What does it mean to be in the eclipse phase?

Answer 4

The eclipse phase is a stage in the viral life cycle which complete infective virions are not yet present. It’s a phase where viral components are actively being synthesized.

Question 5

What is the size of a virion compared to full cells?

Answer 5

• Virions are significantly smaller than full cells.
• They typically range in size from 20 nanometers to 1000 nanometers, while full cells can be much larger.

Question 6

What are the basic parts of a virus (capsid, etc.)?

Answer 6

The basic parts of a virus include:
Genetic material (DNA or RNA)
Capsid (protein coat)
Some viruses may have an envelope (lipid membrane)
Spikes on the viral surface

Question 7

What is the source of a viral envelope?

Answer 7

• The viral envelope is derived from the host cell’s membrane.
• When certain viruses exit the host cell, they acquire a portion of the host cell membrane, which becomes their envelope.

Question 8

What is a spike composed of? What is the role of viral spikes?

Answer 8

• Spikes are composed of protein-carbohydrate complexes on the viral surface.
• The role of viral spikes is to attach to specific receptor sites on the host cell, facilitating the attachment and entry of the virus into the host cell.

Question 9

What types of nucleic acid can be used for the viral genome?

Answer 9

• Viral genomes can be composed of either DNA or RNA.
• They can be single-stranded or double-stranded, linear or circular, depending on the virus.

Question 10

What is the relative size of the viral genome?

Answer 10

The size of the viral genome can vary widely among different viruses. It can range from a few thousand base pairs to hundreds of thousands of base pairs.

Question 11

What are the two possible viral life cycles?

Answer 11

The two possible viral life cycles are the lytic life cycle and the lysogenic life cycle.

Question 12

There are 5 steps to the lytic life cycle, what are they?

Lytic cycle will result in lysis/death of host cell.

Answer 12

1. Attachment
2. Penetration
3. Biosynthesis
4. Maturation
5. Release

Question 13

What components of the host cell are required (hijacked) by the virus to complete the viral life cycle (think of a few examples)?

Answer 13

Viruses require various components of the host cell, including:
* Host cell’s DNA or RNA polymerases
* Ribosomes and tRNA for protein synthesis
* Energy production machinery of the host cell
* Enzymes and precursors for nucleic acid synthesis

Question 14

What is a provirus vs. a prophage?

Answer 14

A provirus is a viral genome that has been integrated into the host cell’s DNA and remains dormant until activated.
A prophage is a viral genome that has been integrated into the DNA of a bacterial host during lysogeny.

Question 15

Which can leave from the host’s genome?

Answer 15

A prophage (integrated viral genome) can excise from the host’s genome during activation and enter the lytic cycle.

Question 16

Can provirus genes be used by the host cell? Can prophage genes be used by the host cell?

Answer 16

• Provirus genes can potentially be used by the host cell. However, it depends on whether the provirus is actively transcribed and expressed.
• Prophage genes typically remain repressed within the host cell’s genome and are not actively used.

Question 17

When does a prophage become active again?

Answer 17

A prophage becomes active again and excises from the host cell’s genome when triggered by certain environmental factors, such as UV radiation or chemicals.

Question 18

Can a cell infected with a provirus be attacked by virions of the same type?

Answer 18

Yes, a cell infected with a provirus can still be attacked by virions of the same type. The provirus’s presence does not necessarily protect the cell from further viral infections.

Question 19

How does specialized transduction differ from generalized transduction?

Answer 19

• Specialized transduction involves the transfer of specific bacterial genes to another bacterium by a temperate phage during the lysogenic cycle. These genes are adjacent to the prophage integration site and are carried along when the prophage excises.
• Generalized transduction involves the random packaging of bacterial DNA fragments into phage capsids during the lytic cycle. It can transfer any bacterial genes, not necessarily specific ones.

Question 20

The life cycle of viruses that infect animal cells is very similar to that of phages. What are some of the key differences between the two?

Answer 20

One key difference is that animal viruses often enter host cells through receptor-mediated endocytosis or fusion with the host cell membrane, whereas phages typically inject their genetic material into bacterial cells.
Animal viruses may have envelopes derived from the host cell membrane, while phages lack envelopes.
The biosynthesis of animal viruses often occurs in the host cell nucleus, while phage biosynthesis can occur in both the nucleus and cytoplasm.

Question 21

What is special about Retroviruses? What is the name of the important enzyme?

Answer 21

Retroviruses are unique RNA viruses that carry their genetic information in the form of RNA but use a special enzyme called reverse transcriptase to convert their RNA genome into DNA once inside the host cell. This DNA is then integrated into the host cell’s genome as a provirus.

Question 22

What special ability does a provirus have?

Think of activation and replication

Answer 22

A provirus of a retrovirus can become activated and replicate on its own, leading to the production of new virions, even while it remains integrated into the host cell’s genome.

Question 23

What is a prion?

Answer 23

A prion is a proteinaceous infectious particle composed of misfolded proteins. Prions are associated with certain neurodegenerative diseases.

Question 24

What is the mechanism for prion-based diseases?

Answer 24

The mechanism of prion-based diseases involves the conversion of normal cellular proteins into abnormal, misfolded forms. These misfolded proteins can then induce other normal proteins to adopt the abnormal conformation, leading to a chain reaction of misfolding. This results in the accumulation of misfolded proteins in the brain, causing neurodegeneration.

Question 25

What are the general characteristics of a prion-caused disease?

Answer 25

Prion-caused diseases are characterized by the accumulation of misfolded proteins in the nervous system, leading to progressive neurological dysfunction, including dementia, muscle stiffness, and eventually death.

Question 26

What does the abbreviation CJD stand for?

Answer 26

CJD stands for Creutzfeldt-Jakob disease, which is a rare and fatal prion-caused neurodegenerative disorder.

Question 27

What is a viroid composed of? What do viroids infect?

Answer 27

A viroid is composed of short pieces of naked RNA. Viroids infect plants and are responsible for various plant diseases.