Question 1

Which of the following best explains why SDS is used in SDS-PAGE for protein analysis?

Accepted Answer

SDS binds to proteins, giving them a constant charge-to-mass ratio and denaturing their tertiary structure.

Question 2

During SDS-PAGE, which protein will migrate fastest through the gel?

Accepted Answer

The protein with the lowest molecular weight.

Question 3

What is the primary function of the stacking gel in SDS-PAGE?

Accepted Answer

To concentrate sample ions into a sharp band before entering the separation gel.

Question 4

Which chemical is commonly used as a reducing agent to break disulfide bonds in protein sample preparation for SDS-PAGE?

Accepted Answer

β-mercaptoethanol

Question 5

A student prepares a polyacrylamide gel with a high %T and constant %C. What effect will this have on the separation of proteins?

Accepted Answer

Smaller pores will form, allowing better separation of low molecular weight proteins.

Question 6

Which equation correctly describes the relationship between voltage, current, and resistance in an electrophoresis system?

Accepted Answer

$$U = I 	imes R$$

Question 7

Why is it important to use gloves when handling acrylamide during gel preparation?

Accepted Answer

Acrylamide is neurotoxic and can be absorbed through the skin.

Question 8

Which staining method is more sensitive for detecting low amounts of protein in SDS-PAGE?

Accepted Answer

Silver stain

Question 9

In SDS-PAGE, what is the effect of increasing the buffer viscosity on electrophoretic mobility?

Accepted Answer

Electrophoretic mobility decreases as viscosity increases.

Question 10

A protein sample is treated with SDS and dithiothreitol (DTT) before SDS-PAGE. What is the role of DTT?

Accepted Answer

DTT reduces disulfide bonds, converting them to thiol groups.

Question 11

Which of the following best describes the molecular sieve effect in gel electrophoresis?

Accepted Answer

Smaller molecules migrate faster through the gel matrix than larger molecules.

Question 12

What is the main reason for using calibration standards in SDS-PAGE?

Accepted Answer

To determine the molecular weight of unknown proteins by comparison.

Question 13

Which of the following statements about isotachophoresis in the stacking gel is correct?

Accepted Answer

Sample ions are sandwiched between leading and trailing ions, resulting in a sharp band.

Question 14

A researcher wants to separate proteins with molecular weights between 14 kDa and 60 kDa. Which %T range should they select for the polyacrylamide gel?

Accepted Answer

A %T that produces small pores, typically higher %T values.

Question 15

Which property of Coomassie Brilliant Blue allows it to be used for protein quantification after SDS-PAGE?

Accepted Answer

Its absorbance at 595 nm increases upon binding to proteins.

Question 16

What is the effect of running SDS-PAGE at a voltage higher than recommended?

Accepted Answer

It can cause overheating, leading to distorted bands and poor resolution.

Question 17

Which of the following is true regarding the charge of proteins after SDS treatment?

Accepted Answer

Proteins acquire a uniform negative charge proportional to their mass.

Question 18

Why is it necessary to denature proteins before running SDS-PAGE?

Accepted Answer

To eliminate the effects of protein shape and intrinsic charge on migration.

Question 19

Which of the following best describes the role of TEMED in polyacrylamide gel preparation?

Accepted Answer

TEMED acts as a catalyst for the radical polymerization of acrylamide.

Question 20

A protein sample is run on SDS-PAGE and visualized with silver stain. The bands appear black. What is the chemical basis for this observation?

Accepted Answer

Silver ions are reduced to metallic silver at protein sites, forming black deposits.

SDS-PAGE and Gel Electrophoresis: Principles and Applications

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