Q: Which of the following equations best represents the yield of protein extraction, where $$C_f is $$the final protein concentration, $$V_f is $$the final volume, $$C_i is $$the initial protein concentration, and $$V_i is $$the initial volume?

$$\text{Yield} = \frac{C_f \times V_f}{C_i \times V_i}$$

Question 1

Which of the following best describes the main goal of protein extraction in biochemistry?

Accepted Answer

To purify a protein by removing it from its source and solubilizing it in solution.

Question 2

During cell homogenization, which of the following is most likely to be released into the crude extract?

Accepted Answer

Organelles, lipids, carbohydrates, nucleic acids, and proteins.

Question 3

A researcher is attempting to purify a novel enzyme from E. coli. Which of the following steps should be performed first?

Accepted Answer

Homogenize the cells to release the enzyme into solution.

Question 4

Which of the following best explains why buffers are commonly used during cell homogenization for protein extraction?

Accepted Answer

Buffers maintain pH to preserve protein structure and function.

Question 5

A student is extracting beta-galactosidase (lacZ) from E. coli. After cell homogenization, the crude extract contains many biomolecules. Which technique would best help to confirm the presence of lacZ in the extract?

Accepted Answer

Performing an enzyme activity assay specific for beta-galactosidase.

Question 6

Which of the following is NOT typically a component of the crude extract after cell homogenization?

Accepted Answer

Intact cells.

Question 7

Why is it important to keep protein extraction solutions cold during the homogenization process?

Accepted Answer

Cold temperatures slow down protease activity, reducing protein degradation.

Question 8

A scientist is using a detergent during cell homogenization. What is the primary role of the detergent in this context?

Accepted Answer

To disrupt cell membranes and solubilize membrane proteins.

Question 9

After homogenization, a researcher wants to purify a specific protein from the crude extract. Which of the following is the most logical next step?

Accepted Answer

Centrifuge the extract to remove cell debris.

Question 10

Which of the following equations best represents the yield of protein extraction, where $$C_f is $$the final protein concentration, $$V_f is $$the final volume, $$C_i is $$the initial protein concentration, and $$V_i is $$the initial volume?

Accepted Answer

$$	ext{Yield} = \frac{C_f 	imes V_f}{C_i 	imes V_i}$$

Question 11

A researcher finds that after homogenization, the protein of interest is not active. Which of the following is the most likely explanation?

Accepted Answer

The protein was denatured during extraction due to improper buffer conditions.

Question 12

Which of the following best describes the difference between cell homogenization and protein extraction?

Accepted Answer

Cell homogenization disrupts cells to release contents, while protein extraction refers to the overall process of isolating proteins.

Question 13

In a protein extraction experiment, why might a researcher add protease inhibitors to the buffer?

Accepted Answer

To prevent degradation of proteins by endogenous proteases.

Question 14

A student is preparing to extract a protein from a tissue sample. Which of the following would be the best initial step?

Accepted Answer

Add a buffer to the tissue and mechanically disrupt the cells.

Question 15

Which of the following is a potential consequence of using a buffer with the wrong pH during protein extraction?

Accepted Answer

Protein denaturation and loss of function.

Protein Extraction: Principles and Methods

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