Shorter fragments of DNA (those with fewer base pairs) have a higher electrophoretic mobility than larger fragments. Thinking about electrophoresis gels as creating a matrix through which fragments must migrate, briefly explain why the size of a DNA fragment affects its electrophoretic mobility.

Key Concepts

Electrophoresis

Electrophoresis is a laboratory technique used to separate charged particles, such as DNA fragments, based on their size and charge. In this process, an electric field is applied to a gel matrix, causing the DNA fragments to migrate towards the positive electrode. Smaller fragments move more easily through the gel's pores, resulting in faster migration compared to larger fragments, which encounter more resistance.

Gel Matrix

The gel matrix, typically made of agarose or polyacrylamide, serves as a sieve that affects the movement of DNA fragments during electrophoresis. The size of the pores in the gel determines how easily different sized fragments can pass through. Smaller DNA fragments can navigate through these pores more efficiently, while larger fragments are hindered, leading to differences in their migration rates.

Molecular Size and Mobility

Molecular size directly influences the mobility of DNA fragments during electrophoresis. Smaller fragments have a higher electrophoretic mobility because they can travel through the gel matrix with less friction and obstruction. In contrast, larger fragments experience greater resistance due to their size, resulting in slower movement through the gel, which is why size is a critical factor in electrophoretic separation.