Question 1

Which factor primarily determines the speed of migration of proteins in SDS-PAGE?

Accepted Answer

The protein's molecular weight

Question 2

What is the main function of SDS (sodium dodecyl sulfate) in SDS-PAGE analysis?

Accepted Answer

To denature proteins and impart a uniform negative charge

Question 3

Which of the following best describes the role of glycerol in a typical SDS-PAGE sample buffer?

Accepted Answer

It increases the density of the sample so it sinks into the well

Question 4

Bromophenol Blue is included in the SDS-PAGE sample buffer primarily to:

Accepted Answer

Serve as a tracking dye to monitor the progress of electrophoresis

Question 5

A protein with a molecular weight of 200,000 Da is analyzed by SDS-PAGE alongside standards of 10,000 Da, 50,000 Da, 100,000 Da, and 200,000 Da. Where do you expect the band of the protein to appear relative to the standards?

Accepted Answer

At the same position as the 200,000 Da standard

Question 6

Which two applications are typical for SDS-PAGE of proteins?

Accepted Answer

Estimating protein molecular weight and assessing protein purity

Question 7

Why is it not necessary to consider the intrinsic charges of proteins when separating them by SDS-PAGE?

Accepted Answer

Because SDS coats proteins, giving them a uniform negative charge

Question 8

You have a BSA stock solution at 2.5 mg/ml. How many $$\mul of $$this stock do you need to prepare 1 ml of a 0.3 mg/ml solution?

Accepted Answer

$$120\ \mu l$$

Question 9

If 5 $$\mul of a 1.2 mg/ml $$BSA sample is diluted to 90 $$\mul$$, what is the dilution factor?

Accepted Answer

$$18$$

Question 10

A 1.7 mg/ml BSA sample is to be diluted 1:20 with water to a total volume of 120 $$\mul. $$How many $$\mul of $$BSA and water are needed, respectively?

Accepted Answer

$$6\ \mu l$$ BSA, $$114\ \mu l$$ water

Question 11

Which of the following best describes the separation principle of SDS-PAGE?

Accepted Answer

Proteins are separated based on their molecular weight

Question 12

Why is it important to know that proteins A, B, C, and D are monomeric when interpreting SDS-PAGE results?

Accepted Answer

Because the molecular weight determined by SDS-PAGE reflects the monomer size

Question 13

Which of the following is NOT a function of Tris in the SDS-PAGE sample buffer?

Accepted Answer

Acting as a reducing agent

Question 14

During an SDS-PAGE run, how can you tell in the lab that the electrophoresis is complete?

Accepted Answer

When the Bromophenol Blue dye front reaches the bottom of the gel

Question 15

Which of the following best describes the role of captoethanol (β-mercaptoethanol) in SDS-PAGE sample buffer?

Accepted Answer

It reduces disulfide bonds in proteins

Question 16

A researcher loads four monomeric proteins with molecular weights of 10 kDa, 20 kDa, 25 kDa, and 100 kDa into separate wells of an SDS-PAGE gel. After electrophoresis, which protein will be found closest to the top (origin) of the gel?

Accepted Answer

100 kDa

Question 17

If you want to prepare 1 ml of a 0.3 mg/ml BSA solution from a 2.5 mg/ml stock, what is the correct calculation for the volume of stock needed?

Accepted Answer

$$V_1$$ = \frac{$$C_2$$ $$V_2$$}{$$C_1$$} = \frac{0.3 	imes 1.0}{2.5} = 0.12\ 	ext{ml} = 120\ \mu l$$

Question 18

Which structural level of a protein is primarily disrupted by SDS during SDS-PAGE?

Accepted Answer

Tertiary and quaternary structures

Question 19

A student needs to prepare a 1:20 dilution of a protein sample to a final volume of 120 $$\mul. $$What is the correct formula to calculate the volume of the original sample needed?

Accepted Answer

$$V_1$$ = \frac{$$V_2$$}{DF}$$

SDS-PAGE and Protein Electrophoresis: Analytical Chemistry Study Notes

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