Viruses and subviral particles

Question 1

Basic components of viruses

Answer 1

Genetic material, a protein coat, and sometimes an envelope containing lipids. Genetic info may be circular or linear, single- or double-stranded, and composed of either DNA or RNA.

Question 2

Capsid

Answer 2

Protein coat of viruses –> may be surrounded by an envelope composed of phospholipids and virus-specific proteins. Envelope is very sensitive to heat, detergents and desiccation –> enveloped viruses are easier to kill

Question 3

Viruses are considered what type of parasites?

Answer 3

Obligate intracellular parasites

Question 4

Virions

Answer 4

After hijacking a cell’s machinery, a virus will replicate and produce viral progeny, called virions, which can then be release to infect additional cells.

Question 5

How do bacteriophages work

Answer 5

They specifically target bacteria
They do not actually enter bacteria; instead, they inject their genetic material, leaving remaining structures outside the infected cell
Contain tail sheath: can act like a syringe, injecting genetic material into a bacterium
Contain tail fibers: help the bacteriophage recognize and connect to correct host cell

Question 6

What are the two types of single-stranded RNA viruses

Answer 6

positive or negative sense

Question 7

Positive sense

Answer 7

Implies that the genome may be directly translated to functional proteins by the ribosomes of the host cell, just like mRNA.

Question 8

Negative-sense

Answer 8

Negative-sense RNA strand acts as a template for synthesis of a complementary strand, which can then be used as a template for protein synthesis. negative-sense RNA viruses must carry an RNA replicase in the virion for this to occur

Question 9

Retroviruses

Answer 9

Enveloped, single-stranded RNA viruses; usually, the virion contains 2 identical RNA molecules., and an enzyme called reverse transcriptase, which synthesizes DNA from single-stranded RNA. This DNA then integrates into the host cell genome, where it is replicated and transcribed as if it were the host cell’s own DNA.`

Question 10

HIV is an example of what type of virus

Answer 10

Retrovirus

Question 11

What are the different methods of progeny release in virions

Answer 11

Viral invasion may initiate cell death, spilling viral progeny. Host cell may lyse as a result of being filled with extremely large numbers of virions. Or virus can leave the cell by extrusion

Question 12

Extrusion

Answer 12

When a virus leaves the cell by fusing with its plasma membrane; process keeps the host cell alive, and allows for continued use of host cell by virus –> virus in this state is in a productive cycle

Question 13

Lytic cycle

Answer 13

Bacteriophage maximizes the use of the cell’s machinery with little regard for the survival of the host cell. Once host is swollen with new virions, the cell lyses, and other bacteria can be infected. Viruses in the lytic phase are termed virulent.

Question 14

Lysogenic cycle

Answer 14

The virus does not lyse the bacterium, but it may integrate into the host genome as a provirus or prophage. The virus will be replicated as the bacterium reproduces because it is now a part of the host’s genome

Question 15

What may cause a provirus to revert to a lytic cycle?

Answer 15

Environmental factors (radiation, light, or chemicals) may cause the provirus to leave the genome and revert to a lytic cycle. The provirus may extract bacterial genes as it leaves the genome, which allows transduction of genes from one bacterium to another.

Question 16

Evolutionary advantage of some viral infections

Answer 16

Infection with one strain of phage generally makes the bacterium less susceptible to superinfection (simultaneous infection) with other phages. Because the provirus is relatively innocuous, this arrangement may provide an evolutionary advantage.

Question 17

What are prions and viroids

Answer 17

Very small (subviral) particles that can cause disease under certain circumstances.

Question 18

Prions

Answer 18

Infections proteins and are, therefore nonliving things. They cause disease by triggering misfolding of other proteins, usually through the conversion of a protein from an alpha-helical structure to a Beta-pleated sheet. Eventually, protein aggregates form, intefering with cell function

Question 19

Viroids

Answer 19

Small pathogens consisting of a very short circular single-stranded RNA that infect plants. Viroids can bind to a large number of RNA sequences and can silence genes in the plant genome. A few examples of human viroids do exist (e.g. hepatitis D virus).