Question

Which of the following palindromic bases sequences in DNA, can be easily cut at about the middle by some particular restriction enzyme?
A. 5’CACGTA3’ and 3’CTCAGT5’
B. 5’CGTTCG3’ and 3’ATGGTA5’
C. 5’GATATC3’ and 3’CTACTA5’
D. 5’GAATTC3’ and 3’CTTAG5’

Answer 1

Palindromic sequences in DNA are the bases that read the same on both strands either 5 to 3 or 3 to 5 directions. Different types of palindromic sequences are recognized by a restriction endonuclease.

Complete answer:
The restriction enzymes are called molecular scissors and are responsible for cutting DNA. restriction enzymes serve as chemical knives to cut genes into defined fragments. Restriction enzymes are obtained only from prokaryotes. It is their natural defense mechanism against bacteriophage infection. Some restriction enzymes such as EcoRI cut the strand of DNA a little away from the center of the palindrome sites, but between the same two bases on the opposite stands. This leaves single-stranded portions at the ends. There are overhanging stretches called sticky ends or cohesive ends on each strand.
5’GAATTC3’ and 3’CTTAG5’ is an example of palindrome DNA. Escherichia coli cut 5’GAATTC3’ and 3’CTTAG5 at the middle’.
So, the correct option (D).

Additional Information:
In the year 1963, the two enzymes responsible for restricting the growth of bacteriophages in E.coli were isolated. One of these added methyl groups to DNA (methylase), while the other cut DNA. Restriction enzymes are obtained only from prokaryotes. It is their defense mechanism against bacteriophage infection. There are three types of restriction enzymes though most restriction enzymes employed in genetic engineering are TypeII because they can be used in-vitro to recognize and cut within the specific DNA sequence typically consisting of four to eight nucleotides.

Note: The Nobel Assembly at Karolinska Institute decided to award the Nobel prize in Physiology or Medicine for 1978 jointly to Werner Arber, Dan Nanthans, and Hamilton Smith for the discovery of “restriction enzymes and their application to problems of molecular genetics”