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Shortcut used: Identify the tested biochemical principle, track charge/carbon/electrons or pathway direction, use the passage data, and reject choices that contradict cellular location or chemical behavior.
Solve in 3 steps:
- Mark the given values and the exact target.
- Apply the relevant formula, rule, or concept.
- Check the final value against the options.
Common mistake: Do not choose an option before confirming the exact demand of the question.
Question 4
Multiple Choice Question
Question
PASSAGE 2 — PROTEIN PURIFICATION
A soluble cytosolic enzyme has an isoelectric point (pI) of 5.2 and forms a disulfide-linked dimer. Scientists purify it at pH 7.5 using anion-exchange chromatography, then size-exclusion chromatography. They analyze samples by SDS-PAGE with and without a reducing agent. The native dimer has a molecular mass of 80 kDa, and its two subunits have equal mass.
QUESTION 4: Why can this protein bind to an anion-exchange column at pH 7.5?
Explanation
Correct Answer: D
ANSWER
Correct Answer: D
Method / Topic: Biochemistry
The correct answer is D: It is negatively charged because pH is above pI. At a pH above its pI, a protein has a net negative charge. An anion exchanger has positively charged groups that retain negatively charged molecules. The column name refers to the ion being bound, not the charge of the stationary phase.
Why this answer is correct
The correct option matches the required rule and the given information.
Short Explanation
The correct answer is D: It is negatively charged because pH is above pI. At a pH above its pI, a protein has a net negative charge. An anion exchanger has positively charged groups that retain negatively charged molecules. The column name refers to the ion being bound, not the charge of the stationary phase.
Detailed Explanation
Question
PASSAGE 2 — PROTEIN PURIFICATION
A soluble cytosolic enzyme has an isoelectric point (pI) of 5.2 and forms a disulfide-linked dimer. Scientists purify it at pH 7.5 using anion-exchange chromatography, then size-exclusion chromatography. They analyze samples by SDS-PAGE with and without a reducing agent. The native dimer has a molecular mass of 80 kDa, and its two subunits have equal mass.
QUESTION 4: Why can this protein bind to an anion-exchange column at pH 7.5?
ANSWER
Correct Answer: D
Method / Topic: Biochemistry
At a pH above its pI, a protein has a net negative charge. An anion exchanger has positively charged groups that retain negatively charged molecules. The column name refers to the ion being bound, not the charge of the stationary phase. To solve this kind of MCAT biochemistry
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Question 4
Learn + Solve: Shortcut, Trap & Fast Route Click to view shortcut, steps, and common mistake
Learn + solve
Shortcut used, common trap, and the fastest solving route
Shortcut used: Identify the tested biochemical principle, track charge/carbon/electrons or pathway direction, use the passage data, and reject choices that contradict cellular location or chemical behavior.
Solve in 3 steps:
- Mark the given values and the exact target.
- Apply the relevant formula, rule, or concept.
- Check the final value against the options.
Common mistake: Do not choose an option before confirming the exact demand of the question.
Question
PASSAGE 2 — PROTEIN PURIFICATION A soluble cytosolic enzyme has an isoelectric point (pI) of 5.2 and forms a disulfide-linked dimer. Scientists purify it at pH 7.5 using anion-exchange chromatography, then size-exclusion chromatography. They analyze samples by SDS-PAGE with and without a reducing agent. The native dimer has a molecular mass of 80 kDa, and its two subunits have equal mass. QUESTION 4: Why can this protein bind to an anion-exchange column at pH 7.5?
Explanation
Correct Answer: D
ANSWER
Correct Answer: D
Method / Topic: Biochemistry
The correct answer is D: It is negatively charged because pH is above pI. At a pH above its pI, a protein has a net negative charge. An anion exchanger has positively charged groups that retain negatively charged molecules. The column name refers to the ion being bound, not the charge of the stationary phase.
Why this answer is correct
The correct option matches the required rule and the given information.
Short Explanation
The correct answer is D: It is negatively charged because pH is above pI. At a pH above its pI, a protein has a net negative charge. An anion exchanger has positively charged groups that retain negatively charged molecules. The column name refers to the ion being bound, not the charge of the stationary phase.
Detailed Explanation
Question
PASSAGE 2 — PROTEIN PURIFICATION
A soluble cytosolic enzyme has an isoelectric point (pI) of 5.2 and forms a disulfide-linked dimer. Scientists purify it at pH 7.5 using anion-exchange chromatography, then size-exclusion chromatography. They analyze samples by SDS-PAGE with and without a reducing agent. The native dimer has a molecular mass of 80 kDa, and its two subunits have equal mass.
QUESTION 4: Why can this protein bind to an anion-exchange column at pH 7.5?
ANSWER
Correct Answer: D
Method / Topic: Biochemistry
At a pH above its pI, a protein has a net negative charge. An anion exchanger has positively charged groups that retain negatively charged molecules. The column name refers to the ion being bound, not the charge of the stationary phase. To solve this kind of MCAT biochemistry
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