Proteins: Structure and Types · Zoology

The 'isoelectric point' (pI) of an amino acid is the pH at which:

  1. The amino acid carries a net positive charge
  2. The amino acid carries a net negative charge
  3. The amino acid carries no net electrical charge
  4. The amino acid undergoes structural denaturation
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Correct answer: The amino acid carries no net electrical charge

The isoelectric point (pI) is the pH at which an amino acid exists as a zwitterion — the positive charge on the protonated amino group exactly balances the negative charge on the deprotonated carboxyl group, yielding zero net charge. At this pH the molecule will not migrate in an electric field.

Difficulty: Medium Question 7 of 20

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