Exercise to Calculate Length of DNA Fragments from Agarose Gel Migration Rates
Scientists make use of the observation that linear DNA fragments migrate during electrophoresis through the agarose gel at a rate that is inversely proportional to the logarithm of their molecular weight. For convenience, molecular weight is expressed as numbers of base pairs (bps). You can use a ruler on your gel or a photograph of your gel to measure the distance each band of DNA has migrated from the sample well and construct a graph that relates distance migrated to the base-pair size of the fragment. You graph a "standard curve" from fragments of known molecular weight on semilog graph paper and then use the plot to derive the bp size of fragments of unknown size that have run on the same gel side by side with the standard. Try it out following the step-by-step directions below:
1A
1B
M
M 1
23,130
9,416
6,557
4,361
2,322
2,027