AAMC FL Practice Exam

What is the purpose of gel electrophoresis in molecular biology?

1. To amplify DNA sequences

2. To separate and analyze DNA fragments

3. To purify proteins

4. To measure DNA concentration

The correct answer is: To separate and analyze DNA fragments

Gel electrophoresis is a widely used technique in molecular biology primarily for the separation and analysis of DNA fragments. The process involves applying an electric current to a gel matrix, typically made of agarose or polyacrylamide, which allows DNA fragments to migrate through the gel. Because DNA molecules are negatively charged due to their phosphate backbone, they move towards the positive electrode when subjected to an electric field. The size of the DNA fragments affects their movement through the gel; smaller fragments migrate faster and travel further compared to larger fragments. This size-dependent migration allows researchers to separate DNA fragments based on their length. After electrophoresis, the gel is often stained, enabling visualization of the separated DNA bands. This separation is crucial for various applications, such as checking the results of a PCR reaction, performing restriction fragment length polymorphism (RFLP) analysis, or isolating specific DNA fragments for cloning. The other options, while related to molecular biology, refer to different processes. Amplifying DNA sequences is achieved through techniques like polymerase chain reaction (PCR), protein purification involves methods such as chromatography, and measuring DNA concentration typically requires spectrophotometry or fluorometry, not gel electrophoresis. Hence, the purpose of gel electrophoresis is distinctly