Question

Questions 14 and 15 are based on the following Question 14 (1 mark for each blank) Base analogs are a class of chemical mutagens that have a similar chemical structure to a normal nucleotide such that DNA polymerase cannot differentiate them The base analog, 5-bromouracil, competes with the normal base thymine during DNA replication and results in point mutations (i.e. base substitutions). Normal nucleotide base Analog Br O 5'-bromouracil Normally, 5-bromouracil can pair with adenine just like thymine, but it possible for it to mispair with guanine. Br -H .H-N Sugar Sugar 5-bromouracl Adenine 5-bromcuraci enol form) (keto form) Normal pairing Mispairing

Answer 1

Answer 14-

Thymine has changed to (C) and the Adenine changed to (G)

b)This is an example of input transition where Adenine changes to Guanine and Cytosine changes to Thymine.

Answer 15- Incorporation error has been takes place when any mismatch base has been incorporated into any nucleotide chain and this mismatch base cause replication error which causes permanent mutation.When any misincorporated nucleotide or basesuccessfully escape from exonuclease activity then it causes Replication error. Replication error takes place during replication

b)Yes both type of errors can be corrected by repair mechanism. Like in nucleotide excision repair,incorrect or mismatch bases with few side bases are removed by enzymes and DNA polymerase replaced them with correct bases but sometimes it causes mutation. There are many more ways like BER(Base Excision Repair) SSB(Single Strand Breaks), etc.