Question

Which one of the following palindromic base sequences in DNA can be easily cut at about the middle by some particular restriction enzyme?

• A. 5’ ........GATATG........ 3’
  3’ ........CTACTA........ 5’
• B. 5’ ........CACGTA........ 3’
  3’ ........CTCAGT........ 5’
• C. 5’ ........GAATTC........ 3’
  3’ ........CTTAAG........ 5’
• D. 5’ ........CGTTCG........3’
  3’ ........ATGGTA........5’

Answer 1

The correct option is C 5’ ........GAATTC........ 3’

3’ ........CTTAAG........ 5’
Restriction endonucleases are the enzymes which cleave the DNA by digesting phosphodiester bonds at the specific sequences (recognition sequence) within the DNA. Examples include EcoR I.

Restriction site or the recognition sequence is the site where the DNA is cut by a restriction endonuclease. They are palindromic sequences. For example, EcoR I recognises the palindromic sequence 5' - GAATTC - 3'.

Palindromic sequences are nucleotide sequences that read the same on the two strands when orientation of the reading is kept the same, that is, 5'→3' direction.

For example, option B, GAATTC from 5’ to 3’ on one DNA strand and CTTAAG from 3’ to 5’ in the complementary DNA strand is a palindromic sequence

Hence the correct option is
b. 5’ ........GAATTC........ 3’
3’ ........CTTAAG........ 5’