Question

The recognition sequences of four Type-II restriction enzymes (RE) are given below. The symbol (|) indicates the cleavage site. Identify the RE that generates sticky ends.

• A. RE1 - \( 5' \, \text{G} \, \text{ATCC} \, 3' \)
• B. RE2 - \( 5' \, \text{CTG} \, \text{CAG} \, 3' \)
• C. RE3 - \( 5' \, \text{CCC} \, \text{GGG} \, 3' \)
• D. RE4 - \( 5' \, \text{AG} \, \text{CT} \, 3' \)

Hint:

Sticky ends are generated when a restriction enzyme cuts DNA in such a way that leaves overhanging single-stranded DNA, which can form base pairs with complementary sequences.

Answer 1

The Correct Option is A

In the context of restriction enzymes (RE), sticky ends refer to the overhanging bases created after the enzyme cleaves the DNA molecule. These ends are essential for ligating DNA fragments together, as they provide complementary sequences for base pairing. - RE1: The recognition sequence is \( 5' \, \text{G} \, \text{ATCC} \, 3' \). When this restriction enzyme cuts between the G and A, it generates sticky ends with overhangs of single-stranded DNA that can pair with complementary sequences. Thus, RE1 generates sticky ends.
- RE2: The sequence \( 5' \, \text{CTG} \, \text{CAG} \, 3' \) cuts between the G and C bases, but this results in blunt ends, not sticky ends.
- RE3: The sequence \( 5' \, \text{CCC} \, \text{GGG} \, 3' \) also results in blunt ends, as it cuts directly in the middle of the recognition sequence.
- RE4: The sequence \( 5' \, \text{AG} \, \text{CT} \, 3' \) similarly results in blunt ends as the cleavage occurs between the A and G bases.
Thus, the only enzyme that generates sticky ends is RE1, so the correct answer is (A).