Question 1

During the first step of a Western blot, cells are lysed and the lysate is centrifuged. What is the main purpose of this centrifugation step?

Accepted Answer

To remove insoluble cell debris from the protein solution

Question 2

SDS-PAGE is a critical step in Western blotting. What is the primary function of SDS in this process?

Accepted Answer

To give all proteins a uniform negative charge

Question 3

After SDS-PAGE, proteins are transferred to a membrane. Which of the following best explains why this transfer is necessary?

Accepted Answer

It enables the detection of specific proteins using antibodies

Question 4

In a Western blot, what is the main purpose of the blocking step after protein transfer?

Accepted Answer

To prevent non-specific binding of antibodies to the membrane

Question 5

Which of the following best describes the role of the primary antibody in a Western blot?

Accepted Answer

It binds specifically to the protein of interest on the membrane

Question 6

What is the function of the secondary antibody in a Western blot?

Accepted Answer

It binds to the primary antibody and is usually conjugated to an enzyme for detection

Question 7

A researcher runs an SDS-PAGE gel and observes that all proteins migrate toward the positive electrode. What property of SDS-treated proteins causes this migration?

Accepted Answer

Uniform negative charge imparted by SDS

Question 8

Why is it important that the secondary antibody in a Western blot is conjugated to an enzyme such as horseradish peroxidase (HRP)?

Accepted Answer

The enzyme catalyzes a reaction that produces a detectable signal

Question 9

During the boiling step in sample preparation for SDS-PAGE, what is the main effect on the proteins?

Accepted Answer

Disruption of secondary and tertiary structures, resulting in denatured proteins

Question 10

A Western blot shows three bands at 25 kDa, 50 kDa, and 75 kDa after probing with a specific antibody. What does this indicate about the protein sample?

Accepted Answer

There are three different proteins recognized by the antibody, possibly isoforms or degradation products

Question 11

Which of the following best explains why proteins must be denatured before running an SDS-PAGE gel?

Accepted Answer

To ensure that migration through the gel is based solely on molecular weight

Question 12

In the context of Western blotting, what is the main reason for using both a primary and a secondary antibody rather than just a labeled primary antibody?

Accepted Answer

Amplification of the detection signal due to multiple secondary antibodies binding to each primary antibody

Question 13

A student forgets to add the blocking buffer after transferring proteins to the membrane in a Western blot. What is the most likely result?

Accepted Answer

High background signal due to non-specific antibody binding

Question 14

Which of the following equations best describes the relationship between the migration distance ($d$) of a protein in SDS-PAGE and its molecular weight ($M$)?

Accepted Answer

$d \propto -\log_{10}(M)$

Question 15

In a Western blot, which of the following best describes the specificity of the secondary antibody?

Accepted Answer

It binds to the constant region (Fc) of the primary antibody

Question 16

A researcher is using a Western blot to detect a protein that is present at very low abundance. Which modification would most likely increase the sensitivity of detection?

Accepted Answer

Using a secondary antibody conjugated to a chemiluminescent enzyme

Question 17

If a protein sample is not fully denatured before SDS-PAGE, what is the most likely consequence for the migration pattern on the gel?

Accepted Answer

Proteins may migrate based on both size and shape, leading to inaccurate molecular weight estimation

Question 18

Which of the following best describes the role of the reducing agent (such as β-mercaptoethanol) in sample preparation for SDS-PAGE?

Accepted Answer

It breaks disulfide bonds, allowing proteins to fully denature

Question 19

A Western blot experiment uses a mouse primary antibody and a goat anti-mouse secondary antibody. What would happen if a goat primary antibody was used instead?

Accepted Answer

The secondary antibody would not bind, resulting in no signal

Question 20

In a Western blot, why is it important to use a molecular weight marker (ladder) alongside your samples?

Accepted Answer

To estimate the molecular weight of detected proteins by comparing their migration distance to known standards

Western Blotting: Principles, Steps, and Applications

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