Q3 of 71 Page 40

The enzyme DNA polymerase in E. coli is a DNA dependent polymerase and also has the ability to proof-read the DNA strand being synthesised. Explain. Discuss the dual polymerase.

1) In bacteria there are three types of DNA polymerases.

2)All the three DNA polymerases can add nucleotides in 5’-3’ direction.


3) DNA III polymerases can proofread the newly formed strand and can sense the wrong base insertions.


4) It deletes wrong base and correct the mistakes by putting the right base in.


5) It cannot correct the substitution of uracil in place of thymine.


6) It can repair the damage done to DNA by UV rays exposure.


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Distinguish between heterochromatin and euchromatin. Which of the two is transcriptionally active?

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Given below is the sequence of coding strand of DNA in a transcription unit 3 'A A T G C A G C T A T T A G G – 5’ write the sequence of a) its complementary strand b) the mRNA