$$\text{Specific Activity} = \frac{\text{Total Activity (units)}}{\text{Total Protein (mg)}}$$

Question 1

Which of the following best describes the principle behind 'salting out' during protein purification?

Accepted Answer

Protein solubility decreases at high salt concentrations, causing them to precipitate.

Question 2

In size-exclusion chromatography, which protein will elute first from the column?

Accepted Answer

The largest protein by molecular weight.

Question 3

A protein mixture is loaded onto a cation-exchange column at pH 7. Which protein will elute first?

Accepted Answer

The protein with the most negative net charge.

Question 4

Which of the following statements about SDS-PAGE is correct?

Accepted Answer

Proteins are separated almost exclusively based on their molecular weight.

Question 5

A researcher wants to purify a protein that binds specifically to ATP. Which chromatography method should be used?

Accepted Answer

Affinity chromatography

Question 6

During isoelectric focusing, a protein will migrate until:

Accepted Answer

It reaches a region where the pH equals its isoelectric point ($$pI).$$

Question 7

Which of the following best describes the difference between Sanger’s method and Edman degradation for protein sequencing?

Accepted Answer

Sanger’s method identifies only the N-terminal residue, while Edman degradation sequentially removes and identifies each N-terminal residue.

Question 8

A protein sample is subjected to two-dimensional electrophoresis. What two properties are being separated in this technique?

Accepted Answer

Isoelectric point ($$pI) $$and molecular weight

Question 9

Which of the following equations correctly defines specific activity of an enzyme preparation?

Accepted Answer

$$	ext{Specific Activity} = \frac{	ext{Total Activity (units)}}{	ext{Total Protein (mg)}}$$

Question 10

Which of the following is a key advantage of High-Performance Liquid Chromatography (HPLC) over traditional column chromatography?

Accepted Answer

It allows for faster separation and higher resolution due to high-pressure pumps.

Question 11

A protein has a $$pI of 4.6. In $$which buffer would it have the greatest net negative charge?

Accepted Answer

pH 7.0

Question 12

Which of the following reagents would you use to cleave a polypeptide specifically at methionine residues?

Accepted Answer

Cyanogen bromide

Question 13

Which step is essential before sequencing a large protein with multiple disulfide bonds?

Accepted Answer

Breaking the disulfide bonds using a reducing agent such as dithiothreitol (DTT).

Question 14

Which of the following best explains why affinity chromatography can achieve high specificity in protein purification?

Accepted Answer

It separates proteins based on highly specific interactions with a ligand attached to the stationary phase.

Question 15

A protein sample is analyzed by SDS-PAGE and shows two bands. What does this indicate about the protein?

Accepted Answer

The protein contains two subunits of different molecular weights.

Question 16

Which of the following best describes the relationship between DNA and protein sequences?

Accepted Answer

Each amino acid in a protein is encoded by a specific triplet of nucleotides in the DNA sequence.

Question 17

Which of the following statements about protein purification is correct?

Accepted Answer

A protein is considered pure when further purification steps do not increase its specific activity and only a single protein species is detected.

Question 18

Which of the following best describes the function of dialysis in protein purification?

Accepted Answer

It separates proteins from small molecules by exploiting differences in size across a semipermeable membrane.

Question 19

Which property of proteins is primarily exploited in isoelectric focusing?

Accepted Answer

Isoelectric point ($$pI)$$

Protein Analysis Techniques and Protein Structure: Study Notes for Biochemistry

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