Microbiology Lab Review: Chapter 12

Lab Review

Chapter 12: Effect of UV Radiation on Bacterial Growth

1.    [CH-12-01] Define terms mutation, wild-type, mutant –

Mutation: Any change in chromosomal structure or a nucleotide sequence of DNA.

Wild-type: Organism that has phenotype and genotype that is predominant in population.

Mutant: Organism that carries the genetic mutation that has affected phenotype.

2.    [CH-12-02] What is the difference between spontaneous mutation and induced mutation? –

Spontaneous mutation: Caused by a natural process in the cell.

Induced mutation: Caused by exposure to factors increasing mutation rate.

3.    [CH-12-03] What kind of damage UV causes to DNA? What effect this damage has on cell growth? –

Destabilizes double bond of a nitrogenous base and causes the formation of thymine dimers, which distort DNA and can lead to breaks in DNA strands.

4.    [CH-12-04] Define the term mutagen. Give examples of mutagens –

Mutagen: An agent that causes genetic mutation. Ex: UV, nitrous acid, ethidium bromide, ethylene oxide.

5.    [CH-12-05] What is the mechanism of mutagenic action of nitrous acid on DNA? –

HNO2 modifies adenine into hypoxanthine OR cytosine into uracil. Results in DNA replication with AT pair changed to CG pair.

6.    [CH-12-06] Both nitrous acid and ethidium bromide cause mutations in DNA. Which compound is more dangerous? Explain your answer –
Ethidium bromide is more dangerous as an intercalating agent it adds additional bases to DNA and causes a frameshift mutation. The frameshift mutation is more likely to disrupt regular DNA functions than pair changes.

7.    [CH-12-07] In your experiment with exposure of bacterial cultures to UV light, how could you tell apart the colony formed by a wild-type bacterium from the colony formed by a mutated bacterium? –

Changes to colony morphology such as a transition from smooth, circular colonies to rough, lobate colonies.

8.    [CH-12-08] Explain the molecular basis for sickle-cell disease –
A point mutation in the ß-globin gene that changes glutamic acid into valine. Responsible for changing the shape of RBC into a sickle shape.

9.    [CH-12-09] Describe bacterial morphology, oxygen and temperature requirements for Deinococcus radiodurans –

Coccus, tetrad grouping, obligate aerobe, optimal growth at 25-30ºC

10. [CH-12-10] After exposure of a bacterial strain to UV light and growing it on nutrient agar, you have noticed that in addition to original type of white and shiny (reflecting the light) colonies a new type of colony appeared in bacterial culture that were white and matte (not reflecting the light).  What structure in bacterial cell was most likely affected by mutation in bacterial DNA (chromosome)? –
Capsule.