Isoelectric point

We know that Amino acids have different charges (+/-/ neutral) and they join together through peptide bond to form peptides and proteins. These Proteins are amphoteric in nature as amino acids are amphoteric. As a chameleon can change its colour based on the surrounding, an amphoteric molecule can either act as an acid or base based on the medium.
In simple words, according to the pH of the medium the charge on the protein will differ.
The pH at which there is no Net charge on the protein is known as its Isoelectric point.
At a pH below their pI, proteins carry a net positive charge; above their pI they carry a net negative charge.
Since proteins have different combinations of amino acids they will have different net charge.
This overall net charge determines the pI of the protein. Thus, proteins have different pI values. Which means that different proteins will have different pH value at which their net charge will be zero. And this concept is exploited in isoelectric focusing.

Видео Isoelectric point канала BioMagica