What does kDa mean in SDS-PAGE?
Daniel Johnson
Published Feb 28, 2026
What does kDa mean in SDS-PAGE?
molecular mass
Most macromolecules are large enough to use the kiloDalton (kDa) to describe molecular mass. Molecular weight is not the same as molecular mass. It is also known as relative molecular mass (symbol Mr, where r is a subscript).
What gel would you use to resolve a 25 kDa protein?
This could lead to poor data and poorly resolved bands if samples spill into adjacent wells. Load 20–40 µg total protein per mini-gel well. The gels should be submerged in migration buffer normally containing SDS, except in native gel electrophoresis….
| Protein size | Gel acrylamide percentage |
|---|---|
| 15–100 kDa | 10% |
| 25–200 kDa | 8% |
Can SDS-PAGE calculate molecular weight?
Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) is a reliable method for determining the molecular weight (MW) of an unknown protein. The first step in MW determination of a protein is to separate the protein sample on the same gel with a set of MW standards.
What is the optimal protein size range for a 12.5 gel?
10-70 kDa
Run the gel as recommended by the manufacturer. Note: 1-2 hours at 100 V is standard, but time and voltage may require optimization….SDS-PAGE Gel Electrophoresis Protocol.
| Protein Size | Gel Percentage |
|---|---|
| 10-70 kDa | 12.5% |
| 15-100 kDa | 10% |
| 50-200 kDa | 8% |
| >200 kDa | 4-6% |
How can you speed up the electrophoresis?
Diluting the buffers to 0.5X with distilled or deionized water (a 1:1 mix) can increase the speed of your electrophoresis experiments by up to 25%. Be warned: doing this can also cause your buffer to heat up more quickly, so check in often while your experiment is running!
How much protein should I load in SDS PAGE gel?
Ideally, it is best to load ≤2 µg per well of a purified protein or ≤20 µg of a complex mixture like whole cell lysates if you are doing Coomassie stain only.
Is SDS-PAGE same as Western blot?
SDS-PAGE is an electrophoresis method that separates proteins by mass. Western blot is an analytical technique to identify the presence of a specific protein within a complex mixture of proteins, where gel electrophoresis is usually used as the first step in procedure to separate the protein of interest.
How is KDa calculated in SDS-PAGE?
Based on the values obtained for the bands in the standard, the logarithm of the molecular weight of an SDS-denatured polypeptide and its relative migration distance (Rf) is plotted into a graph. So the inverse log is 10^1.3305= 21.4kDa for the molecular weight of the unknown protein.
How does SDS-PAGE calculate protein size?
Use a graphing program, plot the log (MW) as a function of Rf. Generate the equation y = mx + b, and solve for y to determine the MW of the unknown protein. Run the standards and samples on an SDS-PAGE gel. Process the gel with the desired stain and then destain to visualize the protein bands.
How do you know if the protein gel has run for long enough?
Running the gel longer will separate your bands more, but it will also cause the bands to become more faint, and they could disappear completely. If you’re not sure whether your gel has run long enough, you can always take it out, look at it on the UV transilluminator (as described below) and put it back to run longer.
Do lower percentage gels have larger pores?
Pore size distribution is the set of the sizes of pores that exist in the gel – in a more concentrated gel, the largest pore that exists is likely to be smaller than in a less concentrated gel.
How does SDS-PAGE work?
In SDS-PAGE, the detergent SDS and a heating step determine that the electrophoretic mobility of a single kind of protein is only affected by its molecular weight in the porous acrylamide gel. SDS PAGE Preparation:
How does SDS-PAGE work with poly-acrylamide gel?
Being present a electricity, proteins migerate towards the negative anode inside the poly-acrylamide gel under denaturing conditions. In SDS-PAGE, the detergent SDS and a heating step determine that the electrophoretic mobility of a single kind of protein is only affected by its molecular weight in the porous acrylamide gel.
How long should I run SDS-PAGE for?
As for the total running time, stop SDS-PAGE running when the downmost sign of the protein marker (if no visible sign, inquire the manufacturer) almost reaches the foot line of the glass plate. Generally, about 1 hour for a 120V voltage and a 12% separating gel.
How can I make a SDS-PAGE gel with a specific mw?
In order to target proteins with MWs between 20 and 200 kDa, you will need to create a conventional SDS-PAGE gel using the recipes shown below. The percentage of gel you require corresponds with the MW of your target protein. Dissolve compounds thoroughly. Adjust pH slowly to pH 8.8 with concentrated HCl, then add ddH2O to 1000ml.
