Question 1

Which property is commonly exploited during protein purification to separate proteins from a mixture?

Accepted Answer

Differences in protein properties such as size, charge, and polarity

Question 2

In the context of protein purification, what does the term 'purification' most accurately refer to?

Accepted Answer

Isolating a protein of interest so that it is the only batch of protein molecule in solution

Question 3

Which of the following is NOT a typical step in a protein purification strategy?

Accepted Answer

DNA replication

Question 4

A scientist wants to purify a nuclear transcription factor from a cell extract. Which sequence of purification steps is most appropriate?

Accepted Answer

Extraction → Differential Centrifugation → Salting Out → Dialysis → Chromatography

Question 5

Which purification technique would be most effective for separating proteins based on their net charge?

Accepted Answer

Ion exchange chromatography

Question 6

During protein purification, which method is primarily used to separate proteins based on their size?

Accepted Answer

Gel filtration chromatography

Question 7

If a protein is highly hydrophobic, which purification technique would best exploit this property?

Accepted Answer

Hydrophobic interaction chromatography

Question 8

Which equation best describes the relationship between the rate of sedimentation ($s$) and the mass ($m$) of a protein during differential centrifugation?

Accepted Answer

$s = \frac{m}{f}$

Question 9

A researcher uses salting out to precipitate a protein. Which salt is most commonly used for this process?

Accepted Answer

Ammonium sulfate ($(NH_4)_2SO_4$)

Question 10

Which of the following best explains why dialysis is used during protein purification?

Accepted Answer

To remove small molecules and salts from a protein solution

Question 11

A protein sample is subjected to affinity chromatography. What is the main principle behind this technique?

Accepted Answer

Separation based on specific binding interactions

Question 12

Which step in protein purification is most likely to remove cellular debris and organelles?

Accepted Answer

Differential centrifugation

Question 13

A scientist is purifying a protein and notices that after salting out, the protein is still contaminated with nucleic acids. Which additional step would best remove these contaminants?

Accepted Answer

Ion exchange chromatography

Question 14

Which of the following is a major advantage of using affinity chromatography in protein purification?

Accepted Answer

It can achieve high specificity for the target protein

Question 15

During protein purification, which step is most likely to be affected by the pH of the buffer solution?

Accepted Answer

Ion exchange chromatography

Question 16

A protein has a pI (isoelectric point) of 5.0. During ion exchange chromatography at pH 7.0, what is the net charge of the protein?

Accepted Answer

Negative

Question 17

Which purification technique would be most suitable for isolating a protein that binds specifically to DNA?

Accepted Answer

Affinity chromatography using a DNA column

Question 18

A researcher is purifying a protein and wants to monitor its purity after each step. Which method is most commonly used for this purpose?

Accepted Answer

SDS-PAGE

Question 19

Which of the following best describes the role of 'salting out' in protein purification?

Accepted Answer

It precipitates proteins by reducing their solubility

Question 20

A protein sample is purified using gel filtration chromatography. Which equation best describes the elution volume ($V_e$) of a protein in relation to the column volume ($V_c$) and the fraction of the column accessible to the protein ($K_{av}$)?

Accepted Answer

$V_e = V_0 + K_{av}(V_c - V_0)$

Protein Purification: Concepts and Strategies

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