Sharper Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Sharper and links to relevant pages within the course.
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|Rate of Migration|
The net charge of a molecule is the most important factor affecting the mobility of that molecule. The greater the net charge, the greater the mobility or the more quickly the molecule migrates. The net charge of a particular compound depends upon the buffer and the resultant pH set by that buffer. The size and shape of a molecule also influence the rate of migration in that the larger the size, the slower the molecule will move in electrophoresis.The viscosity and the pore size in the support media or gels used for electrophoresis influence the rate of migration. Increased viscosity slows the migration and increasing pore size speeds up the migration.Increased heat increases the rate of migration. Increasing the strength of the electrical field by increasing voltage and increasing the temperature used for the electrophoresis both increase the mobility and rate of migration. When increasing these factors that affect mobility, caution is necessary. Each will lead to an increase in temperature that can possibly denature the sample and alter the characteristics of the support medium. The ionic strength of the buffer and its effect on mobility are more complicated. The ionic strength of the buffer affects the thickness of the ionic cloud, the rate of migration, and the sharpness of the separated solutes. In electrophoresis, a cloud of ions forms over the medium and is composed of buffer ions, sample ions and other nonbuffer ions. Increasing the buffer ionic strength increases the buffer ions in the cloud and slows the movement of solutes and creates sharper bands. However, this also increases heat production.
|Buffers and pH|
The isoelectric point of most proteins is between pH 4.0 and 7.5. In pH 8-9, proteins will take on a negative charge and migrate to the anode. Most protein electrophoresis is performed at pH 8.6.Buffers most commonly used are barbital or tris-boric acid-EDTA buffers. They fix the pH at 8.6, leading to sharper bands and good separations.
|IEF Advantages and Applications|
IEF's greatest advantage is its high resolution, resulting in greater separation of solutes. IEF of serum proteins results in many more bands; these bands are sharper because each pH region is very narrow. Performing IEF is easier because the placement of sample application is not important. The sample and ampholytes can be mixed before application; the ampholytes will migrate, create the gradient, and then the proteins separate and migrate.Some isoenzymes and variant hemoglobins in prenatal screening are separated with IEF. Detection of oligoclonal bands in gamma-globulin is a newer use of IEF. IEF is commonly used as one of the separations in two-dimensional electrophoresis.