By placing the molecules in wells in the gel and applying an electric field, the molecules will move through the matrix at different rates, determined largely by their mass but also their charge and shape which varies widely for proteins.
Electrophoretic mobility of small molecules is greater than the mobility of large molecules with the same charge density thus allowing separation. However, because size, charge and shape all play a role in how a molecule will behave in a native gel most scientists use a SDS-PAGE gel which is predictable. The presence of standards of known size always a calibration curve to be created that can be used to identify the approximate MW of an unknown protein band.
Isoelectric focusing IEF is a technique for separating different molecules by differences in their isoelectric point pI. It is a type of electrophoresis, usually performed on proteins in a gel, that takes advantage of the fact that overall charge on the molecule of interest is a function of the pH of its surroundings. When an IEF gel is poured a pH gradient is established. A protein that is in a pH region above its isoelectric point pI will be negatively charged and will migrate towards the anode positive.
As it migrates through a gradient of decreasing pH, however, the protein's overall charge will increase until the protein reaches the pH region that corresponds to its pI. Louis, MO Subject optional. Email address: Your name:. Example Question 1 : Electrophoresis. Possible Answers: anode.
Correct answer: anode. Explanation : Gel electrophoresis is a technique used to separate molecules based on size or charge. Report an Error. Example Question 2 : Electrophoresis. Which of the following is true regarding the isoelectric point pI? It is a property of both the species and the environment II. It represents the size of the species. Possible Answers: II only. Correct answer: II only.
Explanation : The isoelectric point is the pH at which a charged particle loses its charge and becomes neutral; therefore, the pI is only a property of the species not its environment. Example Question 3 : Electrophoresis. Possible Answers: Proteins that are uncharged at physiological pH can migrate through the gel. Other macromolecules cannot be separated via this method. Proteins are separated based on size in this gel. A protein stops migrating through the gel when its pH equals the pI of the gel.
Correct answer: Proteins that are uncharged at physiological pH can migrate through the gel. And this is why they get separated by size. The other day we looked at how we can use reducing agents like beta-mercaptoethanol BME which, instead of splitting water, donate electrons to split up disulfide bridges that help hold some proteins together.
Notify me of followup comments via e-mail. Skip to content. July 4, July 4, Related Terms:. Edith Widder. The two electrodes of a battery or accumulator have different potentials. The electrode with the higher potential is referred to as positive, the electrode with the lower potential is referred to as negative. The electromotive force, emf in V, of the battery is the difference between the potentials of the positive and the negative electrodes when the battery is not working.
During the battery discharge, the cell voltage U , I. Figure 2: Discharge and charge of a battery: left, potential change of the positive and negative electrodes; right, battery voltage change.
During a battery charge, the cell voltage U , the difference between positive and negative, increases Figs. During normal use of a rechargeable battery, the potential of the positive electrode, in both discharge and recharge, remains greater than the potential of the negative electrode. Texts describing battery anodes or cathodes certainly implicitly consider the case of the discharge.
0コメント