Chapter 4 - Microbiology

Question 1

A give type of virus can have only one type of nucleic acid as its genome, and mature virus does not contain nucleic acid other than its ___1.___

A true cell contains not only its genome, but also ___2.___ , ___3.___ , and ___4.___

Answer 1

1. genome
2. mRNA
3. rRNA
4. tRNA

Question 2

Why might a bacteriophage inject its DNA, while animal viruses do not?

Answer 2

Phage must puncture the bacterial cell wall, while animal viruses can be internalized whole into animal cells (NO CELL WALL)

Question 3

Why are all phages and plant viruses naked?

Answer 3

• Viruses acquire envelopes by budding through host membranes
• Phages and plant viruses infect hosts that possess cell walls
  
  • When viruses begin to exit the cell, the cell wall is destroyed, and host membranes rupture
• There is no membrane in which the remaining viruses must bud; they simply escape in a lytic explosion

Question 4

When phage are first added to a bacterial culture, the number of infective viruses initially decreases before it later increases. Why does this occur?

Answer 4

The initial decrease is due to the simple fact that many phage have injected their genomes into hosts and are no longer infectous

Question 5

Proteins contain no __1.__

Nucleic acids contain no __2.__

Answer 5

1. P (phosphorous)
2. S (sulfur)

Question 6

When two viruses infect the same cell, it is called ___1.___

Answer 6

1. co-infection

Question 7

Mutation of the cell-surface receptor that viruses attach to would be a means for an organism to become resistant to viral infection. Why is this mechanism not common? (2 reasons)

Answer 7

1. The receptor has a specific role in the normal physiology of the host, which a mutation might compromise
2. Viruses generally evolve so rapidly that they can keep up with any changes in the host, but this is not an absolute rule (cells of our immune system keep us alive by keeping up with most microorganisms’ tricks)