A few sentences of answer are enough. (2 marks) (4 marks) 4 marks) 1. (a) What i

Question

A few sentences of answer are enough.

(2 marks) (4 marks) 4 marks) 1. (a) What is the structural difference between uracil and thymine? (b) What are the key components in RNA synthesis? (c) What is in a mature mRNA? 2. (a) What is the function of DNA methyltransferases? Suggest two possible roles of (6 marks) these enzymes (b) What reaction does terminal deoxynucleotidyl transferase catalyse? (2 marks) (c) What is the major functional difference between DNA polymerase I and Klenow fragment? (2 marks)

Explanation / Answer

1. a. The structural difference between uracil and thymine is that, thymine has an additional methyl group at 5-carbon which is not present in uracil. So thymine is also known as 5-methyl uracil.

b. The key components of RNA synthesis are

i. Pentose sugar which is ribose

ii. Nitrogen bases- Adenine and guanine (purines) and cytosine and uracil (pyrimidines)

iii. Phosphate group.

With the help of RNA polymerase the RNA sunthesis takes place.

c. A mature mRNA is the processed mRNA whaich is a transcription unit. It consists of a promoter, a structure gene and a termoinator.

2. a. Function of DNA methyl transferase is to

i. Catalyse the transfer of methyl group to DNA

ii. helps in genetic regulation.

b. Terminal deoxynucleotidyl transferase also known as DNA nucleotidyl transferase (DNTT) is a special DNA polymerase expressed in immature pre-B and pre-T lymphoid cells. It catalyses the addition of nucleotides to the 3' terminus of DNA molecule. It does not require a template.

c. DNA polymerase -I helps on filling the nucleotides between okazaki fragments on the lagging strand (after the removal of RNA primer) in 5'-3' direction.

Kleunow fragment is the large protein fragment produced when DNA polymerase-I from E. coli is enzymatically cleaved by the protesase subtilism. It helps in proof reading and removal of pre-coding nucleotides.

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