Virology

Question 1

What can viruses infect?

Answer 1

• plants
• animals
• bacteria
• fungi
• other viruses

A virus that infects bacteria won’t infect any other thing

Question 2

What are the differences between deasd and alive viruses?

Answer 2

Dead
1. inert
2. no cell compounds
3. no metabolism
4. no autonomy

Alive
1. Nucleic aicd
2. proteins
3. mutate
4. grow and multiple
5. react

Inert= onactive when not in a host
No autonomy= cannot survive on their own

Question 3

True or false

All viruses have a nucleic acid and a protein coat

Answer 3

True

Question 4

What is the structure of a virus?

Answer 4

1. Nucleic acid
   
   • encodes virus genes
2. protein coat
   * protective
   * enzymatic
3. envelope (lipid bilayer)
   * matrix protein

Spikes attach to receptor sites on host cells. Phages attach by tail fibers.
Enveloped viruses have a lipid bilayer obtained from a host cell.
Enveloped viruses are more susceptible to disinfectant because damage to the envelope does not allow them to infect

Question 5

What are the 3 shapes of viruses?

Answer 5

1. Icosahedral
2. helical
3. complex

Question 6

What is the description of a icosahedral shape?

Answer 6

20 flat triangles

Question 7

What is the description of a helical shape?

Answer 7

capsomeres arranged in helix

Question 8

What is the description of a complex shape?

Answer 8

• phage
• icosahedral nucleocapsid (head)
• helical protein (tail)

Question 9

What are bacteriophages?

Answer 9

1. infect bacteria
   * lytic
   * temperate
   * filamentous

bacteriophages enter and leave the bacteria via the F pilus
exit the host by lysing the cell

Question 10

What is lytic?

Answer 10

lyse the host cells and then end of infection

Question 11

What is temperate?

Answer 11

lytic or lysogenic

Question 12

What is filamentous?

Answer 12

• rod shaped
• requries an F-pilus

Question 13

What is horizontal gene transfer in bacteriophages?

Answer 13

Transduction
* generalized
* specialized

Question 14

What is generalized horizontal gene transfer?

Answer 14

• Bacterial DNA that has been degraded can accidently packaged with new phage heads
• Some viruses contain only fragmented bacterial DNA, these viruses cannot drive replication, but can incorporate into newly infected cell

Question 15

What is specialized horizontal gene transfer?

Answer 15

• Bacterial DNA is excised with virus DNA when going from lysogenic to lytic
• When incorporated into Phage it is defective, can also be incorporated into targets DNA

Question 16

What is a bacteriophage?

Answer 16

a virus that infects bacteria

Question 17

What is a capsomere?

Answer 17

proteinaceous subunit of a capsid

some capsomeres are composed of only a single type of protein, whereas others are composed of several different kinds of proteins.

Question 18

What is present in a viruses extracellular state?

Answer 18

virions have capsids-protein coats that provide both protection for viral nucleic acid and a means by which many viruses attach to their hosts’ cells.

Question 19

What is a capsid made of?

Answer 19

capsomeres

Question 20

What is a nucleocapsid?

Answer 20

nucleic acid surrounded by a capsid

Question 21

What are the three basic shapes of virions?

Answer 21

Helical, polyhedral, and complex

Question 22

True or False?

All viruses lack cell membranes

Answer 22

True

Question 23

True or False

Animal viruses have an envelope similar in composition to a cell membrane surrounding their capsids

Answer 23

True

Question 24

What is a virion called when it lacks an envelope?

Answer 24

non-enveloped or naked

Question 25

What are the 5 steps of the animal virus infection cycle?

Answer 25

1. attachment (absorption) 2. genome entry 3. synthesis 4. assembly 5. release

Question 26

What happens in a lytic replication cycle?

Answer 26

1. **Attachment** of the virion to the host cell 2. **Entry** of the virion or its genome into the host cell 2. **Synthesis** of new nucleic acids and viral proteins by the host cell’s enzymes and ribosomes 3. **Assembly** of new virions within the host cell 4. **Release** of the new virions from the host cell

Question 27

Where are most DNA viruses located?

Answer 27

Nucleus

Question 28

Where do most RNA viruses develop?

Answer 28

solely in cytoplasm

Question 29

During viral replication, how are enveloped viruses released?

Answer 29

by budding ## Footnote can result in persistent infections

Question 30

How are naked viruses released?

Answer 30

exocytosis or lysis

Question 31

What are acute infections?

Answer 31

* Rapid onset; short duration * Burst of virions released from infected host cell * Immune system gradually eliminates virus

Question 32

What are persistent infections?

Answer 32

* continue for years or lifetime * may or may not have symptoms ## Footnote Can be chronic or latent

Question 33

What is a chronic infection?

Answer 33

continuous production of low levels of virus particles ## Footnote carriers may lack symptoms, but still transmit the virus

Question 34

What is a latent infection?

Answer 34

viral genome remains silent in host cell; can reactivate to cause productive infection

Question 35

What is a prion?

Answer 35

are proteinaceous infectious agents * Linked to slow, fatal human diseases; animal diseases * Usually transmitted only within a species * Composed solely of protein; no nucleic acids

Question 36

What are the characteristics of prions?

Answer 36

Cellular PrP * made by all mammals * normal, functional structure has α-helices Prion PrP * Disease-causing form has β-pleated sheets * Prion P r P causes cellular P r P to refold into prion P r P

Question 37

# True or False Normal sterilization procedures do not deactivate prions

Answer 37

True

Question 38

How are prions destroyed?

Answer 38

Prions destroyed by incineration or autoclaving in concentrated sodium hydroxide