Monday, September 13, 2010

The Potential of Neutrality

Thanks to the existance of surface charges (namely, overall surface charges) existing on proteins, we can make sure of it to seperate proteins using a method known as electrophoresis. Electrophoresis, the migration of macroions as goverened by pH and electric fields, drifts proteins across a surface or differing pH levels, to the point where the pH of the surface allows for the protein to achieve its Isoelectric point (the point where its overall net charge is zero, thereby preventing any more movement caused by applied potentials). Noted is that the protein doesn't just instantly stop at this point, it has to oscillate a bit first as it slows down.

One of the great discoveries from electrophoresis is the differing of sickle cells from normal red blood cells. Despite not knowing the sequence of hemoglobin, Pauling et al found that there had been a change in the sequence as the titration curve of sickle cells was 1/5 of a pH unit different to normal hemoglobin. As it has since been found, a valine is replaced with glutamic acid, which is more acidic, causing the lowering of the titration curve.


  1. Electrophoresis is brilliant. It can also be used for DNA as this polymer has an overall negative charge. The molecules are separated out according to their size. The longer the molecule the slower it migrates through the gel. It's used in most scientific analyses.

  2. Those older scientists always impress me. With such simple techniques they discover so much.

  3. not to mention as well heather, another form of gel running involves the use of putting a sample instead in the gel, and applying a charge, using size seperation instead of charge seperation, since as you mentioned, larger molecules move slower, which comes as a result of restricted movement through the spaces in the gel