Ch.13

Question 1

Viruses that infect bacteria are referred to as?

Answer 1

bacteriophages or phages

Question 2

Viruses are NOT made of cells. What are they made of?

Answer 2

viruses are made of genetic information such as DNA or RNA (nucleic acids) within protective protein coat

Question 3

What shapes can viruses be?

Answer 3

Three shapes:
1. Icosahedral: 20 flat triangles
2. Helical: Capsomeres arranged in helix
3. Complex viruses: Phage/ Icosahedral nucleocapsid (head) and helical protein (tail)

Question 4

What is a filamentous phage and what Is the name of the filamentous phage discussed in class?

Answer 4

• Single-stranded DNA phages that look like long fibers
  – Cause productive infections
  – Infected cells do not die but more slowly than uninfected cells
• M13 is a filamentous phage that initiates infection by attaching to a protein on the F pilus of E. coli

Question 5

Which type of phage can enter both the lytic and lysogenic cycles?

Answer 5

Temperate (lysogenic) Phage

Question 6

What is an enveloped virus?

Answer 6

• surrounded by lipid bilayer obtained from host cell
• their matrix protein is between nucleocapsid and envelope

Question 7

When classifying viruses, they are commonly referred to by their

Answer 7

species name or by another name
- Neither of which is capitalized or italicized

Question 8

When looking at a plaque assay, what causes the holes (plaques) in the plague assay?

Answer 8

bacterial lysis

Question 9

How does entry into the host cell differ between bacteriophages and animal viruses?

Answer 9

Bacteriophage attachment:
1. Phage attaches to receptors
2. Genome entry
- T4 lysozyme degrades cell wall
- Tail contracts, injects genome through cell wall and membrane –> capsid outside cell
Animal Virus attachment:
- Enveloped viruses enter by fusion or endocytosis
- Non-enveloped viruses cannot fuse, enter by endocytosis
- Entire virion enters cell; nucleic acid separates from protein coat in process of uncoating

Question 10

How do animal viruses exit the host cell?

Answer 10

• enveloped viruses leave via budding
• Non-enveloped viruses released when host cell dies by apoptosis initiated by virus or host

Question 11

What is antigenic shift?

Answer 11

• When two different viruses or strains infect a host, new viral particles contain segments from each virus
• New subtype results from this reassortment – process called antigenic shift

Question 12

What are the different methods used to cultivate viruses?

Answer 12

• Viruses must be grown in appropriate host
  – inoculating live animals
  – preparing embryonated (fertilized) chicken eggs
• Process animal tissues to obtain primary cultures (Cell culture or tissue culture)
• Cells divide slowly and only a limited number of times
• Tumor cells used, multiply indefinitely

Question 13

How do plant viruses enter host cells?

Answer 13

• Do not attach to cell receptors
• Enter via wounds in cell wall, spread through cell openings (plasmodesmata)

Question 14

What are prions?

Answer 14

• Prions are proteinaceous infectious agents
  – Composed solely of protein; no nucleic acids
  – Linked to slow, fatal diseases in humans and animals

Question 15

What kinds of organisms can experience spongiform encephalopathy?

Answer 15

animals like cattle from prions

Question 16

What are viroids and what kind of organisms do they infect?

Answer 16

• Viroids are small single-stranded RNA molecules that form a closed ring
• only found in plants; cause serious disease
• Enter through wound sites