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Key Difference – Gel Electrophoresis vs SDS Page

Gel electrophoresis is a technique which separates macromolecules in an electrical field. It is a common method in Molecular biology to separate DNA, RNA and proteins from mixtures according to their molecular sizes. SDS Page is a type of gel electrophoresis which is used to separate proteins from a protein mixture based on their sizes. Gel electrophoresis is a term used to refer to the normal technique applied for DNA, RNA, and protein separation while SDS Page is a one type of gel electrophoresis. This is the key difference between gel electrophoresis and SDS Page.

1. Overview and Key Difference
2. What is Gel Electrophoresis
3. What is SDS Page
4. Side by Side Comparison – Gel Electrophoresis vs SDS Page
5. Summary

What is Gel Electrophoresis?

Gel electrophoresis is a common technique used in laboratories to separate charged molecules such as DNA, RNA, proteins, etc. from their mixtures. A gel is used in gel electrophoresis. It acts as a molecular sieve. There are two types of gels used in gel electrophoresis namely agarose and polyacrylamide. Selection of a gel and gel preparation are important factors to be considered in gel electrophoreses since the pore size of the gel should be carefully manipulated for a good separation of molecules through gel electrophoresis. Gel electrophoresis has an electric field connected to two ends of the gel. One end of the gel shows a positive charge while the other end is negatively charged.

DNA and RNA are negatively charged molecules. Once they are loaded into the gel from the negative end of the gel and applied to the electric field, they migrate through the gel pores towards the positively charged end of the gel. The speed of the migration depends on the charge and the size of the molecule. Smaller molecules easily migrate through the gel pores than larger molecules. Hence, smaller molecules travel a long distance through the gel and the larger molecules travel a short distance. To observe the traveling of molecules on the gel, special types of dyes are used. The electric field is applied for a certain time period and stopped to prevent the loss of molecules and to keep the molecules at their traveled positions. Different bands can be observed in the gel. These bands represent the molecules of different sizes. Hence, gel electrophoresis is useful to differentiate molecules according to their sizes.

Gel electrophoresis is incorporated into various techniques as a preparative technique in Molecular biology such as PCR, RFLP, cloning, DNA sequencing, southern blotting, genome mapping, etc.

Difference Between Gel Electrophoresis and SDS Page

Figure 01: Agarose gel electrophoresis

What is SDS Page?

Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS Page) is a type of gel electrophoresis used to separate proteins. When gel electrophoresis is used to separate proteins, special treatments are needed since proteins are not negatively charged like DNA and RNA and don’t migrate toward the positive end or negative end. Hence, proteins are denatured and coated with a negative charge prior to gel electrophoresis. It is done using a detergent called sodium dodecyl sulfate (SDS). The gel electrophoresis which uses SDS and a polyacrylamide gel for the supporting medium is known as SDS Page. This technique is commonly used in biochemistry, genetics, forensics and molecular biology.

During SDS Page, proteins are mixed with SDS. SDS unfolds proteins into a linear shape and coats them with a negative charge proportional to their molecular mass. Due to the negative charge, protein molecules migrate toward the positive charge end of the gel and separates according to their molecular masses. In SDS Page, polyacrylamide is used as the solid support for the gel. The actual separation of the proteins mainly depends on the properties of the gel. Hence, polyacrylamide gel preparation should be carefully done and correct concentrations of polyacrylamide should be used. Polyacrylamide gels show high resolution than agarose gels. Hence, SDS Page is considered a high-resolution technique for protein separation.

SDS Page is a type of denaturing gel electrophoresis. It has a major limitation in protein analysis. Since SDS denatures proteins prior to separation, it does not allow the detection of enzymatic activity, protein binding interactions, protein cofactors, etc.

Key Difference - Gel Electrophoresis vs SDS Page

Figure 02: SDS page

What is the difference between Gel Electrophoresis and SDS Page?

Gel Electrophoresis vs SDS Page

Gel electrophoresis is a method performed to separate macromolecules using an electric field. SDS Page is a high-resolution gel electrophoresis technique used to separate proteins based on their mass.
Gel Run
It can be performed in a  horizontal or vertical manner. SDS Page always runs vertically.
Basis for Separation
Separation occurs according to the charge and size. Protein separation occurs according to the mass and charge.
Agarose gel electrophoresis has low resolution and polyacrylamide gel electrophoresis has a higher resolution SDS Page has a better resolution.
Gel electrophoresis includes both denaturing and non denaturing techniques. SDS Page denatures proteins prior to separation.

Summary – Gel Electrophoresis vs SDS Page

Gel electrophoresis is a common technique used for separation and analysis of DNA, RNA and proteins based on their size and charge. There are two main types of gel electrophoresis namely agarose gel electrophoresis and polyacrylamide gel electrophoresis. Agarose gels are used mainly for nucleic acid separation; when higher resolution is required, polyacrylamide gels are used. SDS Page is a type of gel electrophoresis commonly used to separate complex mixtures of proteins. It is considered as a high-resolution protein separation technique. This is the difference between gel electrophoresis and SDS Page.

1. Nowakowski, Andrew B., William J. Wobig, and David H. Petering. “Native SDS-PAGE: High Resolution Electrophoretic Separation of Proteins With Retention of Native Properties Including Bound Metal Ions. N.p., May 2014. Web. 7 Apr. 2017
2. Stellwagen, Nancy C. “Electrophoresis of DNA in agarose gels, polyacrylamide gels and in free solution.” Electrophoresis. U.S. National Library of Medicine, June 2009. Web. 07 Apr. 2017

Image Courtesy:
1. “Gelelektrophoreseapparatur” (CC BY-SA 3.0) via Commons Wikimedia
2. “DNA Agarose gel electrophoresis” By School of Natural Resources from Ann Arbor – DNA lab (CC BY 2.0) via Commons Wikimedia