SDS-PAGE Molecular Weight Calculator

Determine protein sizes precisely using standard marker migration distances today.

1. Marker Distances

Enter migration distances from the top of the resolving gel, separated by commas.

2. Marker Weights

Enter corresponding standard molecular weights in kDa, separated by commas matching the distances.

3. Target Protein

Enter the migration distance of your protein of interest to compute its mass.

Formula Used

Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) allows protein separation based primarily on size. The relative mobility ($R_f$) or migration distance ($d$) of a protein is inversely proportional to the logarithm of its molecular weight. The linear relationship used for interpolation and estimation follows:

$$\log_{10}(\text{MW}) = A \times d + B$$

Where:

How to Use This Calculator

  1. Input your standard marker migration distances sequentially in millimeters or centimeters separated by commas into the first column.
  2. Provide the matched standard molecular weights in kiloDaltons (kDa) in the exact same comma-separated order within the second column.
  3. Enter the distinct migration distance measured for your unknown protein of interest inside the third input field.
  4. Click the Calculate Weight button to process the mathematical regression and render the exact estimated molecular size values above.

Comprehensive Guide to SDS-PAGE Protein Analysis

Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis serves as an indispensable cornerstone technique across molecular biology, biochemistry, and proteomics research laboratories worldwide. By denaturing proteins with an anionic detergent, SDS imparts a uniform negative charge-to-mass ratio across polypeptide chains, causing proteins to migrate solely according to their molecular dimensions through the sieve-like matrix of a polyacrylamide gel.

Significance of Standard Curves

Because electrophoresis conditions can vary between runs, absolute migration distances cannot be compared universally without reference controls. Researchers run a mixture of known molecular weight standards—often called protein ladders—alongside experimental samples. By plotting the known logarithmic weights against their measured migration lengths, an inverse linear standard curve emerges, granting high analytical precision.

Interpreting Regression Quality

The reliability of your calculated molecular weight heavily depends on the linearity of the standard curve, denoted statistically by the $R^2$ coefficient. An $R^2$ value close to 1.0 indicates optimal experimental consistency and pipetting accuracy, whereas lower values suggest gel anomalies, smiling effects, or measurement errors during analysis.

Frequently Asked Questions

The migration of proteins through a polyacrylamide mesh has an inverse exponential relationship relative to mass. Taking the logarithm transforms this curvilinear exponential decay into a straight-line function, enabling accurate linear regression interpolation.