Gel Electrophoresis
Simulate gel electrophoresis to separate DNA fragments by size using an electric field through an agarose gel matrix. Visualize how negatively charged DNA molecules migrate toward the positive electrode, with smaller fragments traveling faster and farther than larger ones. Learn applications in DNA fingerprinting, RFLP analysis, and forensic identification.
SORTING MOLECULES BY SIZE
**Gel electrophoresis** is a laboratory technique used to separate mixtures of DNA, RNA, or proteins based on their molecular size and charge. In the case of DNA, which has a consistent negative charge due to its phosphate backbone, the molecules move toward the positive electrode (**anode**). The gel matrix (usually agarose) acts as a molecular sieve: smaller fragments move through the pores faster and farther than larger fragments.
DNA PROFILING AND RFLPs
By using **restriction enzymes** to cut DNA at specific sequences, scientists create fragments of varying lengths (Restriction Fragment Length Polymorphisms, or **RFLPs**). When these fragments are run on a gel, they create a unique banding pattern or "DNA fingerprint." This technique is fundamental in forensics, paternity testing, and evolutionary studies to determine genetic relationships between individuals or species.
HOW TO USE THIS VISUALIZATION
1. **Load the Samples**: Place the DNA ladders and unknown samples into the wells. 2. **Run the Gel**: Apply the electric field and watch the bands migrate through the agarose matrix. 3. **Stain and Analyze**: Use the UV light to visualize the bands and compare the distance traveled to the known standards in the DNA ladder. **Try This**: Compare Sample A and Sample B. Which sample contains the smallest DNA fragment? How do you know based on its position relative to the wells?
CORE FORMULAS
AP EXAM CONNECTION
Unit: Unit 6: Gene Expression and Regulation (Topic 6.8)
Learning Objective: IST-1.P
COMMON MISCONCEPTIONS
- Thinking larger fragments move faster because they are heavier (they move slower due to friction/sieving).
- Confusing the charge of DNA (negative) with its migration toward the positive pole.
- Believing that bands on a gel are single molecules (they are millions of identical molecules).
KEY TAKEAWAYS
- Separates by size and charge.
- DNA moves toward (+) pole.
- Smaller fragments move faster.
- Ladder provides size standards.
- Used for DNA fingerprinting.
PRACTICE QUESTIONS
Q1 (CONCEPTUAL): Which electrode will DNA fragments migrate toward during electrophoresis?
Show Answer & Explanation
Answer: The positive electrode (anode).
Explanation: DNA is negatively charged due to its phosphate groups, so it is attracted to the positive pole of the electric field.
Q2 (CONCEPTUAL): If a researcher wants to separate very small DNA fragments, should they use a higher or lower concentration of agarose in their gel?
Show Answer & Explanation
Answer: Higher concentration.
Explanation: A higher concentration of agarose creates smaller pores in the gel matrix, which provides better resolution for separating small molecules.
