Question

what is different about the ends of restriction fragments produced by the following restriction enzymes?

Answer 1

• restriction enzymes are DNA-cutting enzyme that recognizes specific sites in DNA. They cut DNA at a specific palindromic base sequences, normally 4, 6 or 8 bases long, and are used selectively to cut DNA into defined fragments at sites known as 'restriction sites'. They may make staggered cuts at or near their recognition sites, producing ends with a single-stranded overhang. If two DNA molecules have matching ends, they can be joined by the enzyme DNA ligase. DNA ligase enzyme seals the gap between the molecules, forming a single piece of DNA.

• restriction enzymes that leave single-stranded overhangs are said to produce sticky ends. Sticky ends are helpful in cloning because they hold two pieces of DNA together so they can be linked by DNA ligase.

• example- EcoRI - recognises the sequence 5'GAATTC'3 and produce sticky ends

• Some R.E are “blunt cutters,” which cut straight down the middle of a target sequence and leave no overhang. EXAMPLE- SmaI . Blunt-ended fragments can be joined to each other by DNA ligase but these are harder to ligate together because there are no single-stranded overhangs to hold the DNA molecules in position. HaeIII - recognises the sequence 5'GGCC'3 and produce blunt ends.