A cloning experiment uses the restriction endonuclease EcoRI. Which property of EcoRI makes it useful for joining foreign DNA into a plasmid vector?

• A It cuts DNA at random sites to generate blunt fragments
• B It ligates two DNA fragments after cutting them at the same site
• C It degrades methylated bacterial DNA to protect the vector
• D It recognises a palindromic sequence and cuts asymmetrically to leave single-stranded cohesive ends ✓

Explanation

EcoRI recognises the palindromic hexamer GAATTC and cleaves between G and A on each strand in a staggered fashion, producing complementary 5' overhangs called sticky ends. Fragments cut with the same enzyme have compatible overhangs that anneal and are sealed by DNA ligase. Option A is wrong because Type II enzymes cut at defined recognition sites, not randomly. Option B confuses the nuclease with ligase, which is a separate enzyme added by the experimenter.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.