8: Summary


Plasmids are pieces of DNA that contain recognition sites where restriction enzymes cut the plasmid.

To separate and find out the length of fragments cut by restriction enzymes, scientists use a technique called gel electrophoresis. During gel electrophoresis, fragments of smaller size move faster while those of bigger size move slower.

A connected circle with ‘x’ recognition sites gets broken into ‘x’ pieces while a linear strand with ‘x’ recognition sites gets broken into ‘x+1’ pieces.

With different combinations of restriction enzymes in different lanes, and assuming that everything runs smoothly, there are no overlapping bands, and so on:

  1. The length totals for each lane must…
  2. The number of bands in a multi-enzyme lane (such as A+B) must …
  3. The longest fragment in a multi-enzyme lane cannot be …

Learning Outcomes

After completing this module you should be able to:

  • Describe the use of restriction enzymes to cut plasmid DNA in smaller pieces (fragments)
  • Explain how separation of DNA fragments in gel electrophoresis is based on their size
  • Analyse and interpret experimental data obtained from gel electrophoresis of plasmids
