Gel electrophoresis
Gel electrophoresis is a laboratory method for separating DNA, RNA, or proteins as they move through a gel under an electric field. It is widely used to check PCR products, estimate fragment size, compare samples, and prepare biomolecules for further analysis.
What gel electrophoresis is
Gel electrophoresis is a separation technique used for biomolecules such as DNA, RNA, and proteins. A sample is placed into wells in a gel, an electric field is applied, and molecules migrate through the gel at different rates depending on properties such as size, charge, and shape.
How DNA gels work
DNA fragments have a negatively charged backbone, so they move toward the positive electrode. In an agarose gel, smaller DNA fragments travel through the gel pores more easily and usually move farther than larger fragments during the same run.
The gel matrix
Agarose gels are common for DNA and RNA fragments. Polyacrylamide gels are often used when higher resolution is needed, especially for small DNA fragments or proteins. The gel acts like a molecular sieve, slowing molecules in size-dependent ways.
Ladders and bands
A DNA ladder is a mixture of fragments with known sizes. Running it beside unknown samples gives a scale for estimating fragment length. After staining or imaging, separated molecules appear as bands, with each band representing many molecules of similar size.
After PCR
Gel electrophoresis is often used after PCR to check whether amplification worked. A clear band at the expected size can support that the target sequence was amplified, while missing bands, extra bands, or smears can point to primer problems, contamination, degraded DNA, or poor reaction conditions.
Proteins and other molecules
Gel electrophoresis is not only for DNA. Protein gels can separate proteins by size, charge, or both, depending on the method. SDS-PAGE uses a detergent to give proteins a more uniform charge-to-mass relationship, making size a major factor in separation.
Visualization and interpretation
Separated molecules are usually visualized with stains, dyes, fluorescent labels, or imaging systems. Interpretation depends on controls, ladder placement, sample loading, run time, gel concentration, voltage, and staining method. A gel is evidence, not a complete answer by itself.
Uses
Gel electrophoresis is used in cloning, PCR checks, DNA fingerprinting, restriction digest analysis, sequencing preparation, RNA quality checks, protein analysis, teaching labs, and some diagnostic workflows. It is valued because it is visual, relatively inexpensive, and flexible.
Why it matters
Gel electrophoresis makes invisible molecules visible as patterns. It gives researchers a quick way to compare samples, verify experiments, estimate molecular size, and decide what to do next. Much of molecular biology depends on that simple act of separating and seeing bands.