MediumNEET TEST
+4 / -1
Provided below are recognition sequences for restriction enzymes 1 (RE1), 2 (RE2) and 3 (RE3). Arrows indicate the positions where the enzymes digest on the two strands. Which of the following can the RE1 digested DNA ligate to?
A
All three RE1, RE2 and RE3 digested DNA.
B
Only to RE1 digested DNA.
C
Only to RE1 and RE3 digested DNA.
D
Only to RE1 and RE2 digested DNA.
Explanation
For two pieces of DNA to ligate (stick together), their overhanging single-stranded ends—often called sticky ends—must be perfectly complementary (base-pair matching). Let's look at the sticky ends each enzyme creates by cutting at the arrows: RE1: Cuts between A and A. This leaves an overhang of AGCT. RE2: Cuts between C and A. This also leaves an overhang of AGCT. RE3: Cuts between G and A. This also leaves an overhang of AGCT. Even though the recognition sequences are different for each enzyme, the specific sequence of the overhang is identical for all three: RE1 overhang: 5'-AGCT... RE2 overhang: 5'-AGCT... RE3 overhang: 5'-AGCT... Because the overhangs are identical, they are compatible. RE1-digested DNA will find a perfect base-pairing match with DNA cut by RE2 or RE3. Since all three results in the same AGCT sticky end, they can all ligate to one another.
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