Molecular weight markers are used in gel electrophoresis to estimate the size of DNA, RNA, or proteins. Protein markers are groups of known molecular weight, loaded and separated during the run. DNA markers consist of the bacterial lambda virus and produce reproducible fragments of different sizes. Molecular weight markers are used in genetic engineering, PCR, and forensic science. Some markers are pre-stained and can be used for Western blots.
A molecular weight marker is a molecule used to provide an estimate of the size of molecules subjected to gel electrophoresis. This is a technique in which DNA, RNA or proteins are separated by size, using an electric current on a gel. This term should not be confused with molecular markers in genetics, areas where an organism’s DNA differs from the rest of the population and can be identified with a DNA probe.
Protein molecular weight markers are commonly used when proteins are separated by gel electrophoresis. Molecular weight marker is a group of proteins of known molecular weight, usually supplied by biotechnology companies in a particular size range. The size range is chosen according to the samples under study. The molecular weight markers are loaded together and separated during the run. By measuring the distance traveled by the markers and the protein of interest, the size of the experimental protein can be determined.
Different types of markers can be displayed in different ways. Some of the molecular markers are not labeled and are colored in the gel with the rest of the proteins. They are not visible until the entire gel is stained. Other types of protein molecular markers come pre-stained, and each type of protein has a different color. The separation is visible while the gel is working.
One advantage of a prestained molecular weight marker is for Western blots. This is a technique where proteins are transferred to a membrane and then stained with antibodies to detect a particular protein. Having colored markers helps determine if protein transfer is complete before proceeding with the rest of the procedure.
Molecular weight markers are commonly used to analyze DNA on gels. Often, the molecular markers of DNA consist of the bacterial lambda virus. Restriction enzymes are produced by bacteria to digest the DNA of invading organisms, and HindIII restriction enzyme is often used to degrade lambda DNA. It produces a series of reproducible fragments of different sizes, known as DNA ladders. By comparing the distance traveled by the standards on a logarithmic scale, the size of the DNA fragments analyzed can be determined.
This DNA molecular weight marker can be used to analyze the size of DNA produced during gene isolation and in genetic engineering experiments. It can also be used during polymerase chain reaction (PCR), in which small amounts of DNA or RNA are amplified to produce large amounts of product. PCR techniques are commonly associated with paternity testing and forensic science, but are also very common in basic medical and biological research. Special molecular weight markers are available for smaller products generated by some types of PCR or small RNA molecules.
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