Question

Exposure to various chemicals can cause DNA mutations. Sort the Phrases below as transition, Transversion, or insertion/deletion mutations

Transition Transversion Insertion/ Deletion

1) Replacement of A:T with C:G

2) Treatment with 5 bromouracil causes the replacement of A:T with G:C

3) Oxidative deamination via nitrous acid causes this type of mutation

4) Treatment with dimethyl sulfate causes this type of mutation

5) Replacement of G:C with A:T

6) the removal of one or more base pairs

7) treatment with proflavin causes this type of mutation

Answer 1

1. Base substitution mutation. (Transversion)

2. This is a point mutation.

Explaination: 5-bromouracil (5-BU) is an analogue of thymine that has bromine at the C-5 positon in tne place of CH3 group found in thymine. 5-BU has the same base pairing properties as thymine, and nucleotides containing the base can be added to the daughter polynucleotide at positions opposite as in the template. The common keto form of 5-BU pairs with adenine. But 5-BU confrequently change to the enol form. The mutagenic effect arises because the equilibrium between the two tautomers of 5-BU is shifted more towards the rare enol form that is the case with thymine. It means that during the next round of replication, there is a relatively high chances of polymerases encountering enol-5BU, which (like enol thymine) pairs withG rather than A. This results in a point mutation.

3. Deaminating agents cause point mutations by removal of amino group from bases. Such chemicals are nitrous acid, which deaminates adenine, cytosine and guanine( thymine has no amino group and so cannot be deaminated).

4. Frame shift mutation.

5. Alkylating agents Ex: EMS

6. Substitution mutation. it may be transition or transversion mutation.

7.Proflavin is an interchelating agent. They are usually assosciated with single nucleotide- pair insertions and deletions( frameshift mutation).

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