Question

Gene manipulation is a fast emerging science. It started with the development of recombinant DNA molecules. This technology which mostly involves cutting and pasting of desired DNA fragments is based on two most important discoveries in bacteria - presence of plasmid and restriction endonucleases. The science of r-DNA technology took birth when Cohen and Boyer (1973) were able to produce a piece of gene containing foreign DNA introduced into plasmid of E.coli.

(c) How is the action of exonuclease different from that of endonuclease ?

Hint:

Exonuclease removes nucleotides from the ends of DNA. Endonuclease cuts inside the DNA at specific sites.

Answer 1

Step 1: Recall the two groups:
Both are nucleases, enzymes that cut the phosphodiester bonds of DNA. They differ in where they cut.

Step 2: Exonuclease:
Exonuclease removes nucleotides one by one from the ends of a DNA strand.

Step 3: Endonuclease:
Endonuclease cuts DNA at a specific site inside the strand, away from the ends. Restriction endonucleases cut at palindromic recognition sequences.

Final Answer:
Exonuclease cuts nucleotides from the ends of DNA; endonuclease cuts at specific positions within the DNA.