Question 1

Which buffer is most commonly used to maintain pH in biochemical experiments involving proteins, as referenced in the study materials?

Accepted Answer

Tris buffer

Question 2

During protein extraction, why is it important to keep the sample on ice, as noted in the protocol?

Accepted Answer

To prevent protein denaturation and degradation by proteases

Question 3

If you are instructed to vortex a sample for 5 seconds and then incubate it for 5 minutes, what is the primary purpose of this step in a protein extraction protocol?

Accepted Answer

To ensure thorough mixing and allow buffer components to interact with cellular contents

Question 4

A protocol instructs you to centrifuge a sample at 14,000 rpm for 5 minutes. What is the main reason for this step?

Accepted Answer

To pellet cellular debris and clarify the supernatant containing soluble proteins

Question 5

After centrifugation, you are told to transfer the supernatant to a new tube. What does the supernatant typically contain in a protein extraction protocol?

Accepted Answer

Soluble proteins and other biomolecules

Question 6

Why is it important to avoid disturbing the pellet when transferring the supernatant after centrifugation?

Accepted Answer

To prevent contamination of the protein sample with cellular debris

Question 7

If a protocol requires you to use 50 µL of buffer and vortex, what is the likely reason for using this specific volume?

Accepted Answer

To ensure sufficient buffer for protein solubilization without excessive dilution

Question 8

Suppose you accidentally use 200 µL of buffer instead of 50 µL in a protein extraction. What is the most likely consequence?

Accepted Answer

Dilution of the protein sample, potentially reducing detection sensitivity in downstream assays

Question 9

In a protein extraction protocol, why is it important to use a buffer with a pH close to physiological pH (around 7.4)?

Accepted Answer

To maintain protein structure and function during extraction

Question 10

A protocol instructs you to incubate a sample for 5 minutes after vortexing. If the buffer contains a protease inhibitor, what is the main function of this incubation?

Accepted Answer

To allow the protease inhibitor to interact with and inactivate endogenous proteases

Question 11

If you are preparing a protein sample for SDS-PAGE, why is it important to remove insoluble debris by centrifugation before loading the sample?

Accepted Answer

To prevent clogging of the gel wells and ensure accurate protein separation

Question 12

Which equation best describes the calculation of relative centrifugal force (RCF) in a centrifuge, given the speed in revolutions per minute (rpm) and the radius in centimeters?

Accepted Answer

$$RCF = 1.118 	imes 10$$^{-5}$$ 	imes r 	imes ($$rpm)^2$$

Question 13

A student forgets to vortex the sample after adding buffer. What is the most likely effect on the protein extraction process?

Accepted Answer

Incomplete mixing, leading to inefficient protein solubilization

Question 14

If the protocol requires incubation at room temperature for 5 minutes, but the sample is instead incubated at 4°C, what is the most likely outcome?

Accepted Answer

Slower reaction rates, potentially reducing extraction efficiency

Question 15

Why is it important to use a microcentrifuge tube for protein extraction protocols involving small volumes?

Accepted Answer

To minimize sample loss and facilitate efficient pelleting during centrifugation

Question 16

If a protocol specifies to 'vortex 5 sec, incubate 5 min, centrifuge 5 min,' what is the total elapsed time before collecting the supernatant?

Accepted Answer

10 minutes

Question 17

Which of the following best explains the role of a protease inhibitor in a protein extraction buffer?

Accepted Answer

It prevents degradation of proteins by endogenous proteases during extraction

Question 18

A protocol instructs you to 'vortex, incubate, centrifuge, collect supernatant.' Which step is most critical for ensuring the purity of the protein sample?

Accepted Answer

Centrifugation and careful collection of the supernatant

Question 19

If you are extracting proteins from a tissue sample and the protocol requires you to 'vortex, incubate, centrifuge,' what is the main purpose of these sequential steps?

Accepted Answer

To disrupt cells, solubilize proteins, and separate soluble proteins from debris

Question 20

Which of the following is the best reason for using a buffer during protein extraction from biological samples?

Accepted Answer

To maintain a stable pH and protect proteins from denaturation

Enzyme Kinetics: Michaelis-Menten in Unknown Buffer

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