SDS-PAGE separates proteins mainly on the basis of __________?

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BlackTom AI · Accepted Answer

Restating the question: SDS-PAGE separates proteins mainly on the basis of Molecular Weight.

To understand why, consider what SDS-PAGE does to proteins: Sodium dodecyl sulfate (SDS) is a negatively charged detergent that denatures proteins and coats them with a uniform negative charge proportional to their length. In the polyacrylamide gel, the movement of proteins during electrophoresis is governed primarily by size (the length of the polypeptide chain) because the SDS- coating imposes a near-uniform charge-to-mass ratio across different proteins.

Key mechanism: As all proteins carry similar charge-to-mass ratios after SDS treatment, smaller proteins experience less resistance (smaller drag) in the gel matrix and thus migrate faster toward the positive electrode than larger proteins. This size-dependent migration enables separation by molecular weight.

Important caveats and clarifications: 
- If you run the gel under reducing conditions, disulfide bonds are broken, ensuring that the migration reflects the full unfolded polypeptide chain rather than intact quaternary structures. 
- The gel concentration (percentage of acrylamide) affects resolution: higher acrylamide percentages improve separation of smaller proteins, while lower percentages better separate larger proteins. 
- In the presence of SDS, the intrinsic charge of the protein (such as its isoelectric point) has little influence on migration, because the SDS-induced charge dominates and standardizes the charge-to-mass ratio across proteins.

Common misconceptions addressed: 
- It is not primarily based on native charge or isoelectric point, since SDS disrupts native structure and imposes a uniform negative charge. 
- It is not solely based on shape or structure once SDS has denatured the proteins; after denaturation, shape contributes minimally to mobility compared to size.

In summary, the essential principle is that SDS-PAGE separates proteins mainly by molecular weight due to the uniform SDS-induced charge-to-mass ratio and the gel’s sieving effect, which makes smaller polypeptides migrate faster than larger ones.

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SDS-PAGE separates proteins mainly on the basis of __________?

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When current is applied:

SDS-PAGE gels are made of acrylamide and bis-acrylamide since these two create a small sieving. Mark theINCORRECT statement

the SDS-PAGE gel shown above is the result of an experiment in which a ~55kDa protein is purified from cells, shown in Lane 3. What would you predict lanes 4, 5, and 6 show about the ~55kDa protein? Choose the correct answer from the answers below

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BIOT5621.36986.202530 Exam I Spring 2025 retry

SDS-PAGE separates proteins mainly on the basis of __________?

View Explanation

Log in for full answers

Similar Questions

When current is applied:

SDS-PAGE gels are made of acrylamide and bis-acrylamide since these two create a small sieving. Mark theINCORRECT statement

the SDS-PAGE gel shown above is the result of an experiment in which a ~55kDa protein is purified from cells, shown in Lane 3. What would you predict lanes 4, 5, and 6 show about the ~55kDa protein? Choose the correct answer from the answers below

In SDS-PAGE, which protein migrate most quickly through the gel? Ones that are ______.

SDS-PAGE is ____________ and separates molecules based on ____________

What is the purpose of SDS in SDS-PAGE? Breaks disulfide linkages Unfolds proteins to secondary structure Coats proteins in a negative charge

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Making Your Study Simpler

SDS-PAGE is and separates molecules based on