Great question! Let's break down how the electric current is arranged in gel electrophoresis based on the properties of DNA.
How Electric Current is Arranged in Gel Electrophoresis
1. Charge of DNA
- DNA molecules are negatively charged due to their phosphate backbone.
- This negative charge is consistent regardless of the size of the DNA fragment.
2. Electric Field Setup
- In gel electrophoresis, the gel is placed in a buffer solution that conducts electricity.
- An electric current is applied across the gel with two electrodes:
- The negative electrode (cathode) is placed near the wells where DNA samples are loaded.
- The positive electrode (anode) is placed at the opposite end of the gel.
3. Movement of DNA
- Because DNA is negatively charged, it is attracted toward the positive electrode.
- When the electric current runs, DNA fragments migrate through the gel from the negative (top) to the positive (bottom) end.
- Smaller fragments move faster and travel farther down the gel.
- Larger fragments move slower and remain closer to the top.
Summary
Electrode Position| Charge| DNA Movement Direction
---|---|---
Top (wells)| Negative (cathode)| DNA starts here
Bottom| Positive (anode)| DNA moves toward here
The electric current is arranged so that the negative electrode is at the top (where DNA is loaded) and the positive electrode at the bottom , causing negatively charged DNA fragments to migrate down through the gel. If you'd like, I can also explain how the gel matrix affects the movement of DNA fragments or how scientists estimate fragment sizes using DNA ladders!
