Question

Which of the following restriction enzymes produces blunt ends?

• A. EcoRI
• B. HindIII
• C. SmaI
• D. BamHI

Hint:

A commonly asked comparison is: \[ \boxed{ \begin{aligned} \text{EcoRI} &\rightarrow \text{Sticky Ends} \\ \text{HindIII} &\rightarrow \text{Sticky Ends} \\ \text{BamHI} &\rightarrow \text{Sticky Ends} \\ \text{SmaI} &\rightarrow \textbf{Blunt Ends} \end{aligned} } \] Remember: SmaI = Straight Cut = Blunt End.

Answer 1

The Correct Option is C

Concept: Restriction endonucleases are enzymes that recognize specific DNA sequences and cleave DNA at or near these recognition sites. Depending on the cutting pattern, they produce either sticky (cohesive) ends or blunt ends. Sticky ends possess short single-stranded overhangs, whereas blunt ends have no overhang because both DNA strands are cut at the same position.

Step 1: Understand blunt-end restriction enzymes.
Blunt-end enzymes cut both strands of DNA exactly opposite each other. \[ \boxed{ \text{No Overhang} \Longrightarrow \text{Blunt End} } \] SmaI recognizes the sequence \[ 5'-CCCGGG-3' \] and cuts directly through the center, producing blunt ends.

Step 2: Examples of restriction enzymes.

• EcoRI → Sticky ends
• HindIII → Sticky ends
• BamHI → Sticky ends
• SmaI → Blunt ends Thus, among the given options, only SmaI generates blunt-ended DNA fragments.

Step 3: Applications of blunt ends.
Blunt-ended DNA fragments are useful in:
• DNA cloning
• Construction of recombinant DNA
• Molecular genetics experiments
• Genome mapping Although blunt-end ligation is less efficient than sticky-end ligation, it allows joining of DNA fragments without complementary overhangs. Final Answer: \[ \boxed{Option (C) is correct \]