Question

A restriction enzyme has a 4 bp recognition sequence. Assuming equal frequency of all four bases in a 5,000 bp linear section of DNA, how many fragments (rounded answer) would you expect to see on an electrophoresis gel?

Answer 1

Answer: 20 fragments

Explanation:

This particular restriction enzyme has a 4 bp (base pair) recognition sequence therefore it will cleave once every 4ⁿ bases where n indicates the number pf bases in the recognition sequence.

• The recognition sequence is 4 bp therefore this restriction enzyme cleaves once every 4⁴ = 256 bases. This is the length of the restriction fragment.
• Calculate the number of fragments by dividing the total number of bases ( where you assume equal frequency of bases ie. A+T = C+G) by the length of the restriction base.
• therefore 5000bp/256bp = 19,53 now this number ca n be rounded up to 20.
• The expected number of fragments on the electrophoresis gel will be 20 fragments.