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:
- The length totals for each lane must…
- The number of bands in a multi-enzyme lane (such as A+B) must …
- The longest fragment in a multi-enzyme lane cannot be …
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
If you want a printer-friendly version of this module, you can find it here in a PDF document. This printer-friendly version should be used only to review, as it does not contain any of the interactive material, and only a skeletal version of problems solved in the module.