Biotechnology- Principles and Processes Question 8
8. An enzyme catalysing the removal of nucleotides from ends of DNA is :
[2019, Odisa]
(a) Protease
(b) DNA ligase
(c) Endonuclease
(d) Exonuclease
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Answer : d
Hints & Solutions
(d) Restriction enzymes belong to a larger class of enzymes called nucleases. Nucleases are of two different kinds: exonucleases (which remove nucleotides from the end of a DNA molecule) and endonucleases (which break internal phosphodiester bonds at palindromic sites that are highly specific). DNA ligase helps in ligating/joining DNA fragments. Proteases is an enzyme which breaks down proteins and peptides. DNA Polymerase I possesses a $3^{\prime} \to 5^{\prime}$ exonuclease activity or “proofreading” function, which lowers the error rate during DNA replication, and also contains a $5^{\prime} \to 3$ exonuclease activity, which enables the enzyme to replace nucleotides in the growing strand of DNA by nick translation.
