Electrophoresis: which way does a protein move?
A protein with an isoelectric point of 6.5 is placed in a native gel at pH 8.5. Which way does it migrate?
Answer B: explanation for every choice
A
A protein is positive only at a pH below its pI.
B
Correct. At a pH above its pI, a protein is deprotonated and negatively charged, so it moves toward the positive electrode (anode).
C
A protein has no net charge only at a pH equal to its pI.
D
Negative species move toward the positive anode, not the negative cathode.
TakeawaypH > pI → negative → moves to the anode. pH < pI → positive → moves to the cathode.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb103.