Open Question
Mark the approximate final position of the following tripeptide on the isoelectric focusing gel: Glu-Met-Asp.
Hint: calculate the isoelectric point of the peptide.
5. Protein Techniques
Isoelectric Focusing
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At some point during isoelectric focusing, proteins stop moving through the gel because:
A
The proteins do not have ionized groups at that pH.
B
The proteins have a net charge of zero at that pH.
C
The proteins have a net positive or net negative charge at that pH.
D
Their mass is too large to be moved at that position in the gel.
Verified step by step guidance1
Understand the concept of isoelectric focusing: It is a technique used to separate proteins based on their isoelectric point (pI), which is the pH at which a protein has no net charge.
Recognize that proteins are amphoteric molecules, meaning they can carry both positive and negative charges depending on the pH of their environment.
During isoelectric focusing, proteins are placed in a pH gradient and subjected to an electric field. They will migrate to the region of the gel where the pH is equal to their isoelectric point.
At the isoelectric point, the protein has a net charge of zero, meaning the positive and negative charges on the protein are balanced. This results in the protein no longer moving in the electric field because there is no net charge to drive its movement.
Conclude that the reason proteins stop moving during isoelectric focusing is that they reach a pH where they have a net charge of zero, not because of their mass or lack of ionized groups.
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