MCAT Biochemistry Question 42: Answer and Explanation

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Question: 42

12. How does the gel for isoelectric focusing differ from the gel for traditional electrophoresis?

  • A. Isoelectric focusing uses a gel with much larger pore sizes to allow for complete migration.
  • B. Isoelectric focusing uses a gel with SDS added to encourage a uniform negative charge.
  • C. Isoelectric focusing uses a gel with a pH gradient that encourages a variable charge.
  • D. The gel is unchanged in isoelectric focusing; the protein mixture is treated before loading.

Correct Answer: C

Explanation:

The gel in isoelectric focusing uses a pH gradient. When a protein is in a region with a pH above its pI, it is negatively charged and moves toward the anode. When it is in a pH region below its pI, it is positively charged and moves toward the cathode. When the pH equals the pI, the migration of the protein is halted.

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