BACE - Biotechnician Assistant Credentialing Protein Isolation and Quantification Questions and Answers

Question 1

A biotechnician needs to purify a large batch of a recombinant protein that has been engineered to include a polyhistidine tag (His-tag).
Which type of chromatography would be the MOST effective and specific method for this initial capture step?

Accepted Answer

Immobilized Metal Affinity Chromatography (IMAC)

Answer

Size-Exclusion Chromatography

Answer

Anion Exchange Chromatography

Answer

Hydrophobic Interaction Chromatography

Question 2

When performing a Bradford assay to create a standard curve, a technician observes that the color of the solution changes from brown to blue upon addition of the protein standards. What is the spectrophotometer measuring at 595 nm?

Accepted Answer

The absorbance of the protein-dye complex, where the dye has shifted to its blue form.

Answer

The absorbance of the unbound, reddish-brown form of the Coomassie dye.

Answer

The rate of reduction of copper ions by the protein.

Answer

The intrinsic fluorescence of the protein's tryptophan residues.

Question 3

In SDS-PAGE, what is the primary function of the sodium dodecyl sulfate (SDS) component in the sample loading buffer and the gel running buffer?

Accepted Answer

To denature proteins and impart a uniform negative charge-to-mass ratio.

Answer

To maintain the protein's native three-dimensional structure for activity analysis.

Answer

To cleave proteins into smaller peptide fragments for better resolution.

Answer

To act as a tracking dye to monitor the progress of the electrophoresis.

Question 4

A technician is performing size-exclusion chromatography (SEC) to separate a mixture of three proteins with different molecular weights: Protein A (150 kDa), Protein B (75 kDa), and Protein C (25 kDa). In what order will these proteins elute from the column?

Accepted Answer

Protein A, then B, then C

Answer

Protein C, then B, then A

Answer

All three proteins will elute at the same time

Answer

The order depends on the charge of the proteins

Question 5

A lab needs to accurately quantify the total protein concentration in crude cell lysates that contain a high concentration of detergents, such as Triton X-100. Which of the following quantification methods is generally more suitable and less prone to interference from these detergents?

Accepted Answer

Bicinchoninic acid (BCA) assay

Answer

Direct A280 absorbance

Answer

Bradford assay

Answer

SDS-PAGE with densitometry

Question 6

A biotechnician uses a spectrophotometer to measure the concentration of a purified protein by reading the absorbance at 280 nm (A280). This direct measurement method relies on the presence of which specific components within the protein?

Accepted Answer

Aromatic amino acids like tryptophan and tyrosine

Answer

Peptide bonds

Answer

Proline and glycine residues

Answer

Basic amino acids like lysine and arginine

A biotechnician needs to purify a large batch of a recombinant protein that has been engineered to include a polyhistidine tag (His-tag).Which type of chromatography would be the MOST effective and specific method for this initial capture step?

A biotechnician needs to purify a large batch of a recombinant protein that has been engineered to include a polyhistidine tag (His-tag).
Which type of chromatography would be the MOST effective and specific method for this initial capture step?