Gel Electrophoresis Essay

Thanks to TV shows like CSI, many people are familiar with the use of gel electrophoresis to separate macromolecules like DNA. However, gel electrophoresis can also be used to separate out proteins.

Different proteins have different sizes, mainly due to the number of amino acid building blocks in their structure. Chemical modifications attached to the protein also affect its size. Different proteins also have different charges. This can result from both the types of amino acid used to construct them, as well as the types of modifications attached to them.

Different types of electrophoresis gels are used to provide different types of information. The type of gel you choose therefore depends on the type of question you are asking.

Size Separation Gel electrophoresis
Protein Electrophoresis

Usually, the proteins are first treated with heat and a chemical called SDS in order to unravel the protein. SDS is a detergent that gives all the proteins the same overall negative charge so that when an electric current is applied to the gel, separation is only due to the size of the protein. This technique is called SDS-PAGE (SDS-Polyacrylamide gel electrophoresis).

Small protein molecules move more quickly through the gel than larger proteins, resulting in a series of ‘bands’. Each band contains a protein of a particular size. These can be compared with standards of known sizes.

An SDS-PAGE gel has been used to separate proteins on the basis of size. The samples are the blood of various shark species. The first lane contains markers of known sizes. Large proteins are at the top of the gel and small proteins are at the bottom.

This technique might be used for many purposes, including purifying a particular protein, for example to isolate an enzyme for the food industry.

Charge and pH