Question

I'm a moleculary biology student and have to do a detailed presentation about SDS-PAGE for my next lab.

So I was currently trying to understand the physics of electrophoresis and electrolysis. Since I was never very good at physics I wanted to make sure I understand it correctly:

Am I right in saying, that if I have two electrodes in a non-conducting fluid, that no current will flow and that thus the electrodes are not actually charged but neutral? Since if you have a normal current with a metal wire, current also does not flow, if you have a gap in the wire. The electrones are not waiting and the ends of the wire, if you know what I mean.

So the electrodes are uncharged, right? But if I would take salt water as the fluid, the charge can be balanced by ions, and the electrodes themselves will get charged, if we assume that no Redox reaction occurs. So that there is e.g. the cathode with an excess of electrons, and sodium ions moving towards it and then surrounding it. And the more electrons flow over time, the more sodium ions gather there. Am I picturing this correct? But since water is present, electrolysis could occur and the electrons in the cathode would get less (and more in the anode). But why can it still attract proteins and nucleic acids in electrophoresis, if the electrodes are constantly held neutral? Is it because there are constantly electrones flowing and thus the electrodes are never actually neutral? I must say, trying to understand things in detail is very confusing, especially in physics. I hope someone can help and/or maybe recommend a book or other source where this is explained. Most books and videos only explain it superficially and jump right to equations. Thanks :))

Answer 1

Yes, you are correct. In a non-conducting fluid, such as a typical gel used in SDS-PAGE, the electrodes remain uncharged. However, when using a conducting fluid like saltwater, the charge can be balanced by ions, resulting in charged electrodes. Despite this, in electrophoresis, the electrodes themselves are effectively neutralized over time due to the continuous flow of electrons, allowing them to attract proteins and nucleic acids.

Step-by-step explanation:

In a non-conducting fluid, electrons do not flow between the electrodes, and they remain uncharged. However, when using a conducting fluid like saltwater, the charge can be balanced by ions. For instance, at the cathode, an excess of electrons results in the attraction of positively charged ions like sodium ions. This creates a charged environment around the cathode.

Yet, in the context of electrophoresis, the continuous flow of electrons ensures that the electrodes are never permanently charged. Electrophoresis involves applying an electric field to move charged biomolecules through a gel. While the electrodes may accumulate charges temporarily, the ongoing flow of electrons neutralizes them over time. Therefore, the electrodes are effectively neutral, allowing them to attract proteins and nucleic acids during electrophoresis.

Understanding these electrochemical processes in detail can indeed be complex, especially for those not well-versed in physics. It's crucial to grasp the interplay of ions and electrons in different scenarios, and practical applications like electrophoresis offer a tangible context for comprehending these principles. If you're seeking in-depth explanations, textbooks on electrophoresis or introductory physical chemistry may provide more comprehensive insights.