Question

When you separate a DNA product of a restriction digest on an agarose gel, and you see three bands on the gel spread out between the negative and positive poles, what can you say about the DNA, specifically the sizes of the DNA?

Answer 1

When we separate a DNA product of a restriction digest on an agarose gel and see three bands on the gel spread out between negative and positive poles, then the following points can be elucidated by seeing the DNA and size of the DNA :

Point 1. The restriction digested DNA fragments are separated according to their moleculer size and charge. The more small the size of fragments, the more nearer to the positive pole. Smaller fragments of negatively charged DNA travels faster than the larger fragments through the pores of agarose gel to the positive pole. So, different bands are created according to the size of the fragments. If we start from the positive pole the size of the fragments gradually increases.

Point 2. If we assume that there's no loss of nucleotides in the restriction digestion, then the size of the DNA fragments separated is same as the size of the restriction fragments. And the total size of the DNA which was digested through restriction enzyme is the total size of DNA fragments added together.

Point 3. If the DNA which was digested through restriction enzyme is a circular DNA, then the number of DNA fragments is equal to the number of restriction sites. And if the DNA is a linear DNA then the number of DNA fragments is equal to the number of restriction sites + 1.

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