Microbiology: Viruses

Question 1

What is the structure of a virus?

Answer 1

Capsid, nucleic acid, and protein rich envelope.

- others may include tail base plate, and tail fiber (bateriophages)

Question 2

a mature virus out side the host cell is called a ?

Answer 2

virion

Question 3

How do viruses differentiate from living organisms?

Answer 3

• require host cells reproductive machinery to reproduce
• do not metabolize organic nutrients
• (in active form) are not separated from external environment by a barrier such as a cell wall or membrane
• posses ether DNA or RNA not both
• can be cyrstallized with out losing ability to infect.

Question 4

bacteriophage

Answer 4

virus that infects bacteria

- has tail and fibers

Question 5

Describe a Lytic infectoin

Answer 5

• virus commmandeers the cells reproductive machinery and begins reproducing new virus.
  the cell may fill w/ viruses until it bursts, or it may release viruses one at a time
• A virus folling the lytic cycle is called a ‘Virulent virus’

Question 6

What is Latent Period?

Answer 6

• period from infection to lysis

- this includes the eclips period(brief period after infection before first fully formed virion appears)

Question 7

Describe a Lysogenic Infection

Answer 7

• when the viral DNA is incorporated into the host genome, so when the host replicates its DNA the viral DNA is replicated as well.
• A virus in the lysogenic cycle is called a ‘temperate virus’

Question 8

During a lysogenic infection, while the viral DNA remains incorporated in the host DNAthe virus is said to be _______.
And this type of virus is called a _______.

Answer 8

1. dormant or latent
2. prophage

• a dormant virus can be come active if under some type of stress(UV, carcinogens)

Question 9

vaccine

Answer 9

• either an injection of antibodies or of non-pathogenic virus with the same capsid or envelope.

Question 10

Describe a retrovirus

Answer 10

• a retrovirus carries reverse transcriptase to create DNA from its RNA. The DNA is then incorporated into the host cell.
  ex: AIDS

Question 11

Describe plus-stranded RNA

Answer 11

• indicates that proteins can be directly translates from RNA

Question 12

Describe Minus-stranded RNA

Answer 12

• is the complement to mRNA and must be transcribed to plus-RNA before being translated