Question

The restriction cut by enzyme BamH1 that recognizes a palindromic sequence and leaves one strand longer than the other would produce a DNA that looks like?
A) …GATCC-3’
…C-5’
B) …C -3
…GATCC -5’
C) …G-3’
…C-5’
D) …G -3’
…CCTAG -5’

Answer 1

Restriction enzymes is a specific sequence of nucleotides and it produces a double-stranded DNA. Many of them are palindromic, meaning the base sequence reads the same backwards and forwards

Complete answer:
• Palindromic sequence is a nucleic acid sequence of DNA or RNA molecule in a certain direction (5’to 3’) on one strand and matches the sequence reading in the same direction (5’ to 3’) on the complementary strand.
• In the first, the complementary sequence is different from the coding section, hence different types of cleavage will not occur in the same direction. Blunt ends will be formed as no sticky ends will be formed.
• BamH1 has a recognition site of 5’-GGATCC-3’and cleaves these sequences just after the 5’-guanine on each strand. But in the second case the recognition sites of both the sequences are different for bamh1, leading to blunt ends.
• In the third case, cytosine is present in the place of 5’guanine.
• In the last case, there is the presence of guanine on the 5th end of the sequence. Hence Bamh1 will recognize the restriction site and cleaves on the end forming sticky ends.

Hence, the correct answer is option (D).

Additional information:
Recognition sequences in DNA differ for each restriction enzyme producing differences in the length, sequence and strand orientation (5' end or the 3' end) of a sticky-end of an enzyme restriction.

Note: Always remember the restriction site for BamH1 will be 5’-G/GATCC-3’ and after cleavage it will form sticky overhang structures having G-3' and -CCTAG-5' guanine on both ends.