Last Thursday in class, we did a lab in which we placed DNA segments in a type of gel, sent an electric current through a chamber containing the gel, and watched the segments move across the gel. On either end of the chamber sat two electrodes, positively and negatively charged, respectively. The DNA segments started off at the negatively charged end, and when given an electric current, moved toward the positive end. Why did they move? The phosphate groups in the DNA are negatively charged, meaning they have a greater number of electrons than protons. Since opposites attract, the electrons want to move from the negatively charged end of the chamber to the positive charged end. This interested me as we are also dealing with electrons in my AP Physics class.
This semester in AP Physics, we have learned about charges and how they interact with each other; the most fundamental of charges we have worked with are protons and electrons. One example of how these charges interact is through a process called conduction, in which a charged rod touches a neutrally charged (equal number of protons and electrons) rod, and depending on if the charged rod is positive or negative, the electrons in either rod will move from one to the other in order to make the neutral rod the same charge as that of the charged rod.
Can I apply the knowledge I have of electrons from AP Physics to the AP Biology lab? Well, some might want to know why “opposites attract” in this gel chamber. What is the reasoning for such behavior between the electrons and protons? Between the protons of the chamber end and the electrons of the DNA phosphate groups exists a force of attraction called electric force. If this force did not exist, the electrons would not want to move toward the positively charged end, and the statement “opposites attract” would have no credibility. In fact, electric force bears similarities to the force of gravity. As charges need this electric force in order to attract, we need gravity in order to “attract” to the ground. Without gravity, we could go flying off into space; it is the “electric force” between the ground and us.* A formula exists to calculate the strength of the electric force between two charges, and it is (KxQ1xQ2)/(R^2). In this lab, K is a constant value (9 x 10^9), Q1 is the charge of the electrons in the DNA fragments, Q2 is the charge of the protons on the chamber end, and R is the distance, or radius, between the two charges. Notice that you DIVIDE by the radius, so the smaller the radius, the stronger the force of attraction. This means that as the DNA segments get closer to the chamber end, the force existing between the two charges gets stronger. Unfortunately, the thickness of the gel keeps the DNA fragments from actually reaching the positive end of the chamber.
This is just one example of how electrons function in more than one scientific field of study. Another basic example lies in chemistry, where electrons are found on the orbitals of elements (however, I will leave the explanation of THAT to someone who knows a little more about chemistry than me). Science, although split into different branches of study, always leads toward the same goal: to explain the natural world. In the path toward this similar finishing point, all branches of science overlap and depend on one another at some point or another.
* = Electric force does not ALWAYS make two charges attract. I am talking specifically about opposite charges because those are what we faced in the biology lab. If two charges are both positive or both negative, electric force will repel them.