11.14.1 Viruses and Prions: Living or Nonliving?

Question 1

Viruses and Prions: Living or Nonliving?

Answer 1

• Viruses are noncellular infectious particles composed of a protein capsid and genetic material, either DNA or RNA. Viruses have no metabolic processes and are therefore not considered living. They rely on the components of a host cell in order to replicate themselves.
• Viruses reproduce themselves using either the lytic or lysogenic cycles.
• Prions are infectious protein particles that can cause other proteins to become harmful. Mad cow disease is thought to be caused by prion particles.

Question 2

note

Answer 2

• While structure varies among different viruses, they are all composed of an outer protein coat that encloses the genetic material. Some bacteria, such as the herpes simplex virus, have an outer membrane that encloses the protein coat.

Question 3

lytic cycle

Answer 3

• The lytic cycle of viral reproduction, seen to the left, begins when the virus infects the host cell and injects its genetic material.
• Host cell enzymes are used to make copies of of viral nucleic acids and direct the synthesis of viral proteins. New viruses are assembled. The cell lyses, releasing the viruses

Question 4

lysogenic cycle

Answer 4

• During the lysogenic cycle the viral DNA is incorporated into the host cell’s chromosome. Every time that the host cell replicates, the viral material is also replicated.
• The virus may eventually leave the host cell when a lytic cycle is triggered. Triggers include environmental influences such as chemicals or radiation.

Question 5

Viruses consist of a protein ____________ and genetic material composed of ____________.

Answer 5

• capsid / DNA or RNA

Question 6

True or false?

Antibiotics kill bacteria and viruses.

Answer 6

• false

Question 7

Which statement regarding prions is true?

Answer 7

• Prions are thought to cause other proteins to change their shape.

Question 8

Viruses are not considered living because

Answer 8

• they have no metabolism

Question 9

The lysogenic cycle differs from the lytic cycle in which of the following ways?

Answer 9

• In the lytic cycle the cell lyses and releases copies of the virus.

Question 10

True or false?

Some viruses have an outer membrane composed of lipids, which encloses the protein coat.

Answer 10

• true