1. Mutations, other than those caused by transposable genetic elements, fall int

Question

1. Mutations, other than those caused by transposable genetic elements, fall into which two

categories?

A. Missense and Nonsense

B. Chromosomal and Somatic

C. Phenotypic and Genotypic

D. Missense and Frameshift

2. What is the basis for mutagenesis by ultraviolet light?

A. Photoreactivation repair

B. Excision (or dark) repair

C. Increased frequency of tautomers

D. Induction of a protein that decreases the fidelity of DNA polymerase

E. Recombination (or gap) repair

F. Answers (A) and (B)

G. Answers (B) and (E)

H. Answers (A), (B), and (E)

3. Which of the following are molecular mechanisms of spontaneous mutation?

A. Deamination of bases in DNA

B. Depurination of DNA

C. Mistakes by DNA polymerase (slippage and mis-incorporation)

D. All the above

E. Answers (A) and (B)

F. Answers (B) and (C)

4. Can nitrous acid revert a mutation caused by the intercalating agent ethidium bromide?

A. Yes

B. No

5. Under which of the following conditions would you expect to have a higher mutation rate caused by

use of the mutagen 5-bromouracil?

A. Absence of growth

B. Slow growth under nutrient-limiting conditions

C. Rapid growth, no nutrient limitation

D. None of the above, all would be expected to have the same rates of mutagen-induced

mutation

Explanation / Answer

1.

Mutations caused by transposons occur in the categories of insertion, and frameshift, due to the addition or of transposable DNA elements at any locus. Other mutations result in a substitution of single DNA base, resulting in either missense or Frameshift. Chromosomal, somatic, genotypic and phenotypic mutations are general terms to describe mutations in the gene, type of chromosome, or protein. It does not describe the type of mutation.

So, the answer is (D) Missense and Frameshift.

2.

Exposure to UV results in DNA lesions. These lesions could be repaired by two mechanisms in the cell, namely light (or photoreactivation) repair and dark (or nucleotide excision) repair. Other repair mechanisms, base excision repair, recombination repair are involved in DNA damage caused by exposure to ionizing radiation, reactive species, etc. The basis for mutagenesis by ultraviolet light is Induction of a protein that decreases the fidelity of DNA polymerase.

So, the answer is (D) Induction of a protein that decreases the fidelity of DNA polymerase.

3.

Spontaneous mutations arise due to errors in DNA repair or replication, or interaction of cell metabolites with DNA bases altering the bases. It can include deamination of DNA bases, depurination of DNA and other chemical modifications of the DNA bases. Ultimately, when the cellular DNA repair fails to rectify the damage, it results in the mutation.

Thus, the answer is D All the above.

4.

Nitrous acid causes deamination of DNA bases resulting in transition of AT base pairs to GC base pairs, and vice versa. Ethidium bromide is a DNA intercalating dye that can cause frameshift mutations. Both compounds are mutagenic and have different mechanisms to cause DNA damage.

So, the answer is B: No.

5.

5-bromouracil causes mutation by its insertion in the daughter strand during replication. Its keto form can pair with adenine, and its enol form is complementary to guanine. And the two forms can interchange at any time.

So, in the subsequent round of replication, either adenine or guanine is incorporated opposite 5-bromouracil, and so on. So, in a cell with rapid growth, which occurs under the conditions of ample nutrient availability, the rate of DNA replication is higher, and thus higher chances of mutation due to 5-bromouracil incorporation in DNA.

So, the answer is C: Rapid growth, no nutrient limitation.

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