Read How DNA Fragments Join
Restriction enzymes create compatible DNA ends; ligase seals those ends into a recombinant molecule.
Restriction Enzymes and Ligation is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Cut and join
Cut insert and vector with the same restriction enzyme to create compatible ends. Base pairing aligns the ends, and DNA ligase forms phosphodiester bonds to seal the sugar-phosphate backbone. Joining is performed in vitro.
Count fragments and compare enzyme types
A circular plasmid cut at n distinct sites gives n fragments. Type-I restriction enzymes recognise specific sequences but cut at variable distances rather than at one fixed point within the recognition site.
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- ✓Same enzyme → compatible ends.
- ✓Ligase makes phosphodiester bonds.
- ✓Circular plasmid with four cuts → four pieces.
- ✓Type I cuts away from its recognition site.
Hydrogen bonding pairs the sticky ends; ligase makes the covalent backbone bonds.
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