Question

Which of the following enzymes produces "sticky ends" in DNA?

• A. DNA ligase
• B. Exonuclease
• C. Restriction endonuclease EcoRI
• D. DNA polymerase

Hint:

Remember:
• Restriction Endonuclease $\rightarrow$ Cuts DNA.
• EcoRI, HindIII, BamHI $\rightarrow$ Produce sticky ends.
• DNA Ligase $\rightarrow$ Joins DNA fragments. Sticky ends greatly increase the efficiency of recombinant DNA formation.

Answer 1

The Correct Option is C

Concept: Restriction endonucleases are molecular scissors that recognize specific palindromic DNA sequences and cut DNA at or near these recognition sites. Some restriction enzymes make staggered cuts, producing short single-stranded overhangs called sticky ends. These sticky ends can easily pair with complementary DNA fragments, making them extremely useful in recombinant DNA technology.
• Restriction enzymes are isolated mainly from bacteria.
• They protect bacteria by cutting foreign DNA such as bacteriophage DNA.
• EcoRI is one of the most commonly used restriction enzymes.
• EcoRI recognizes the sequence: \[ 5'-GAATTC-3' \] and produces sticky ends after cleavage.

Step 1: Understand sticky ends.
Sticky ends are short single-stranded DNA overhangs produced when restriction enzymes cut DNA in a staggered manner. For EcoRI: \[ \begin{aligned} 5'-G\downarrow AATTC-3' \\ 3'-CTTAA\uparrow G-5' \end{aligned} \] After cleavage, complementary overhangs are formed that can easily base pair with matching DNA fragments.

Step 2: Eliminate the incorrect options.

• DNA ligase joins DNA fragments together but does not cut DNA.
• Exonuclease removes nucleotides one by one from DNA ends.
• DNA polymerase synthesizes new DNA strands during replication.
• Only EcoRI produces sticky ends by making staggered cuts.

Step 3: Choose the correct option.
Therefore, \[ \boxed{Option (C) is the correct answer. \]