Introduction to viruses

Question 1

People used to believe what small bacteria were viruses?

Answer 1

Mycoplasma and ricketssia

Question 2

What are the hallmarks of viruses (5 things).

Answer 2

1. Strictly intracellular and potentially pathogenic entities with an infectious phase
2. Possess only one type of nucleic acid
3. Multiply in the form of their genetic material
4. Unable to grow and undergo binary fission
5. Devoid of Lipmann system

Question 3

What is the Lipmann system?

Answer 3

series of enzymes for energy production

Question 4

Which virus has both RNA and DNA?

Answer 4

Hepatitis B - has a very short RNA primer and DNA genome

Question 5

are viruses alive?

Answer 5

no

Question 6

Before viruses were discovered, what was the term for the etiologic agents?

Answer 6

Filterable agents

Question 7

What is peculiar of the nomenclature of viruses?

Answer 7

don’t have genus or species

Question 8

What names do viruses have?

Answer 8

vernacular names

Question 9

What is limiting to taxonomy of viruses?

Answer 9

Not much genetic information so there is a limit to phenotypic characteristics to base taxonomy

Question 10

What are some characteristics used to classify viruses?

Answer 10

Type and structure of nucleic acid (DNA/RNA, ds/ss)
Replication strategy (RNA viruses)
Symmetry of capsid
Presence or absence of lipid envelope

Question 11

What are the symmetry types of the viral capsid?

Answer 11

helical or icosahedral

Question 12

What type of viruses acquire a lipid envelope?

Answer 12

those that bud out of host cells - get coated with lipid membrane

Question 13

How are enveloped viruses vulnerable?

Answer 13

Very vulnerable to drying, physical agents like soap, alcohols

Question 14

Which virus type is tougher? Naked or enveloped?

Answer 14

Naked - protein capsids are hard to eradicate

Question 15

Why should you run for soap and water if bitten by a rabbid animal?

Answer 15

Rabbes virus is an enveloped virus

Run for soap, walk for the rabbes shot

Question 16

What is the adsoprtion function of the virion?

Answer 16

1. Adsorb to specific host cell receptors and interact with cell membranes to faciliate entry of the genome into the host cell

Question 17

What is the protective role of the virion?

Answer 17

Protect the genome from environmental threats such as nucleases and UV radiation

Question 18

What is a metabolic role of the virion?

Answer 18

in some virus groups, provides building blocks for the early stages of virus synthesis in host cells

Question 19

what is the general structure of a virion?

Answer 19

One or more nucleic acid molecules surrounded by protein subunits

Question 20

What may surround the protein capsid in viruses? What does it consist of?

Answer 20

Envelope made of host lipids and glycosylated viral proteins

Question 21

How much smaller are viruses than the cells they infect?

Answer 21

100-1000x smaller

Question 22

What are the smallest viruses? What size are they?

What are the largest viruses? What size are they?

Answer 22

Parvoviruses - 20 nm

Poxviruses - 300 nm

Question 23

What are the growth periods of viruses?

Answer 23

Eclipse period

Exponential growth

Question 24

What is the eclispe period?

Time frame?

Answer 24

Virus enters host cell, get disassembly and synthesis of viral components
1-20 hours

Question 25

How long is the exponential growth phase?

How many virions are produced per host cells?

Answer 25

8-72 hours

100-10 000 virions/host cell

Question 26

What are the steps in the replication cycle of viruses?

Answer 26

1. Adsorption
2. Penetration
3. Uncoating
4. Genome replication
5. Assembly and release of progeny viruses

Question 27

What is one of the reasons why respiratory infections are more common during the winter?

Answer 27

Home cannot be humidified to optimum conditions - airways get dry, especially at night - allowing the viruses to stick to the mucosa better and cause infection

Question 28

What is adsorption mediated by?

Answer 28

Mediated by folding of capsid proteins or via glycoprotein spikes which attach to host cell receptors

Question 29

What can block adsoprtion by viruses?

Answer 29

Antibody to virus receptor-binding protein

Question 30

What are the two methods of viral penetration?

Answer 30

1. Receptor mediated endocytosis

2. Fusion of enveloped viruses

Question 31

Stepwise disassembly of the virion that frees the genome.

Answer 31

uncoating

Question 32

What stage of replication cycle of viruses accounts for much of the eclipse period?

Answer 32

uncoating

Question 33

Once manufactured under the guidance of the viral genome, how is a virus produced?

Answer 33

Autoassembles

Question 34

Where do RNA viruses asssemble?

Where do DNA viruses assemble?

Answer 34

RNA virus - cytoplasm (think ribosomes)

DNA virus - nucleus

Question 35

How can viruses exit the host cell?

Answer 35

either produce so many viral particles that the host cell bursts; or released through budding

Question 36

How does viral escape cause inflammation?

Answer 36

Viral-mediated bursting of host cells causes inflammation

Question 37

What are the four outcomes of virus infection of host cells?

Answer 37

1 - Abortive
2 - Permissive
3 - Lysogeny
4 - Lysis of host cell

Question 38

What is abortive infection of host cell?

Answer 38

defective virus - cannot complete cycle

Question 39

What is permissive infection of host cells?

Answer 39

host cell is not killed - replicates alongside host

Question 40

What is lysogeny?

Answer 40

Viral genome is incorporated into the host genome, forming a provirus

Question 41

Patients with viral infections are usually contagious when?

Answer 41

Before they show symptoms

Question 42

How are respiratory viruses transmitted?

Answer 42

Not through air, but through touch from someone infected, then touching your face (e.g. nasolacrimal duct)