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Understanding Isoelectric Point

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Questions and Answers

What is the Isoelectric Point (IEP)?

The point at which the zeta potential is at its maximum value

The point at which the zeta potential is zero, making the molecule electrically neutral (correct)

The point at which the zeta potential is at its minimum value

The point at which the zeta potential changes direction

Which functional group in amino acids acts as a proton acceptor?

Carboxylic acid group

Hydroxyl group

Amino group (correct)

Sulfhydryl group

How can the Isoelectric Point (pI) of molecules with two ionizable groups be calculated?

$pI = pKa1 - pKa2$

$pI = \frac{pKa1 + pKa2}{2}$ (correct)

$pI = pKa1^2 + pKa2^2$

$pI = pKa1 \times pKa2$

For molecules with more than two ionizable groups, how is the Isoelectric Point (pI) calculated?

<p>$pI = \frac{pKa2 + pKa3}{2}$ (A)</p> Signup and view all the answers

Why is the Isoelectric Point (IEP) important for particle stability?

<p>It describes the region at which particle charge is low, indicating conditions for flocculation (C)</p> Signup and view all the answers

Study Notes

Isoelectric Point (IEP)

The Isoelectric Point (IEP) is the pH at which a molecule has no net electric charge.
In amino acids, the amino group (-NH2) acts as a proton acceptor, while the carboxyl group (-COOH) acts as a proton donor.

Calculating Isoelectric Point (pI)

For molecules with two ionizable groups, the pI can be calculated using the Henderson-Hasselbalch equation: pI = (pKa1 + pKa2) / 2.
For molecules with more than two ionizable groups, the pI is calculated by considering the pKa values of each ionizable group and the pH-dependent charges of the molecule.

Importance of Isoelectric Point (IEP)

The Isoelectric Point (IEP) is important for particle stability because it determines the pH range at which a molecule is most stable and least likely to aggregate or precipitate.
At the pI, the molecule has a neutral net charge, which minimizes electrostatic interactions and promotes stability.

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Description

Learn about the concept of isoelectric point, where the zeta potential becomes electrically neutral. Explore how different functional groups on molecules donate or accept protons, focusing on well-known examples like amino acids.