Question 1

In ion-exchange chromatography, which type of column would you use to purify a protein with a net charge of $+3$ at pH 7.0?

Accepted Answer

Cation-exchange column

Question 2

A cation-exchange chromatography column is packed with negatively charged resin. Which of the following proteins will elute last?

Accepted Answer

A protein with net charge $+4$

Question 3

During cation-exchange chromatography, what is the effect of increasing the salt concentration in the elution buffer?

Accepted Answer

It competes with bound proteins, causing them to elute from the column.

Question 4

Which of the following peptides would elute first from a cation-exchange column at neutral pH?

Accepted Answer

A peptide rich in Asp and Glu residues

Question 5

If a mixture contains four proteins with net charges at pH 7.0 as follows: Protein A: $+2$, Protein B: $0$, Protein C: $-2$, Protein D: $+4$, what is the correct order of elution from a cation-exchange column?

Accepted Answer

C, B, A, D

Question 6

A researcher is purifying a protein using cation-exchange chromatography. The protein elutes only after a high concentration of NaCl is added. What does this indicate about the protein's net charge?

Accepted Answer

The protein has a strong positive charge.

Question 7

Which equation best describes the competitive displacement of proteins from a cation-exchange resin by salt ions?

Accepted Answer

$\mathrm{Protein^{+}-Resin^{-} + Na^{+} \rightarrow Protein^{+} + Na^{+}-Resin^{-}}$

Question 8

A mixture of amino acids is separated by cation-exchange chromatography at pH 2.0. Which amino acid will elute last?

Accepted Answer

Lysine ($\mathrm{Lys}$)

Question 9

Which of the following statements about ion-exchange chromatography is correct?

Accepted Answer

Cation-exchange chromatography is used to purify proteins with net positive charge.

Question 10

A peptide with the sequence 'KRGD' (Lys-Arg-Gly-Asp) is loaded onto a cation-exchange column at pH 7.0. Which residue contributes most to its retention on the column?

Accepted Answer

Lysine (Lys)

Question 11

During a cation-exchange chromatography experiment, a student observes that a protein elutes earlier than expected. Which of the following could explain this observation?

Accepted Answer

The buffer pH is below the protein's isoelectric point ($pI$).

Question 12

Which of the following best describes the principle behind the separation of proteins in ion-exchange chromatography?

Accepted Answer

Proteins are separated based on their net charge at a given pH.

Question 13

A mixture of four peptides is loaded onto a cation-exchange column at pH 7.2. Their net charges are: Peptide #1: $+3$, Peptide #2: $+1$, Peptide #3: $-2$, Peptide #4: $0$. What is the correct order of elution?

Accepted Answer

Peptide #3, Peptide #4, Peptide #2, Peptide #1

Question 14

Which of the following changes would increase the retention time of a positively charged protein on a cation-exchange column?

Accepted Answer

Decrease the salt concentration in the buffer

Question 15

A protein with a $pI$ of 5.0 is loaded onto a cation-exchange column at pH 7.0. What is the expected net charge of the protein, and will it bind to the column?

Accepted Answer

Net negative charge; will not bind

Question 16

Which buffer condition would cause a protein with a $pI$ of 9.0 to elute first from a cation-exchange column?

Accepted Answer

Buffer pH 11.0

Question 17

A student is separating a mixture of amino acids using cation-exchange chromatography at pH 3.0. Which amino acid will bind most strongly to the resin?

Accepted Answer

Arginine ($\mathrm{Arg}$)

Question 18

Which of the following is a common misconception about ion-exchange chromatography?

Accepted Answer

Proteins with net negative charge bind strongly to cation-exchange resin.

Question 19

A protein sample is loaded onto a cation-exchange column. The elution profile shows two peaks: one at low salt concentration and one at high salt concentration. What does this indicate about the protein mixture?

Accepted Answer

The mixture contains proteins with different net positive charges.

Ion Exchange Chromatography: Principles and Applications in Protein Purification

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