Thus, the molecule is electrically neutral, but the charge will cancel each other. Isoelectric pH is defined as the pH which a molecule exists as a Zwitter ion (or) dipolar ion and carries no net charge. What is an Isoelectric Point (pI)?Īt which pH, amino acids don’t migrate towards cathode (or) anode under the influence of electric field, is simply called “ Isoelectric point”. Each amino acid has a characteristic pH at which it carries both positive and negative charges and exists as a Zwitter ion. In strongly acidic pH (low pH), the amino acid is positively charged (Cation). CALCULATE PI ISOELECTRIC POINT FREEThe amino acids rarely exist in a neutral form with free carboxyl (-COOH) and free amino (-NH2) groups. Basically the proton shifts from carboxyl group to amino group of the self-molecule at normal pH cellular levels. Zwitterion (or) dipolar ion is a hybrid molecule containing positive & negatively ionic groups. The name zwitter is derived from the German word which means “hybrid”. Thus, dicarboxylic acid like glutamic acid can have three pK values (two for carboxyl groups and one for the amino group) and four types of charged molecules as shown below. Similarly, when the pH is further raised to around 9.8 the amino group is dissociated – this pH is called the pK of an amino group. This is called the pK of the acid group and at this pH, dissociated and undissociated species are found in equal concentrations. However when the pH is raised and reaches around pH 3.0, the proton from the carboxyl group is leaving a -COO- group. In Strong acid conditions (around pH 1.1) the alpha-COOH group remains undissociated.
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