Final answer:
DNA samples should be placed near the negative electrode in gel electrophoresis because DNA's negative charge causes it to move towards the positive electrode, facilitating the separation of fragments by size.
Step-by-step explanation:
When conducting gel electrophoresis, samples of DNA fragments should be placed near the negative electrode. DNA has a negative charge because of the phosphate groups in its backbone, which causes it to be repelled from the negative electrode and drawn towards the positive electrode when an electric current is applied. Because of this, DNA samples are loaded into wells at the side of the gel closest to the negative electrode. During the electrophoresis, smaller DNA molecules will travel faster and further towards the positive electrode through the gel matrix, thus separating the DNA fragments by size.
In gel electrophoresis, samples of DNA fragments are placed on the side of the gel closest to the negative electrode. The gel is composed of a gelatin-like material, typically agarose, and an electric field is applied through the gel. Since DNA has a negative charge, it is attracted to the positive electrode and moves from the negative to the positive electrode. Smaller DNA fragments travel faster through the gel compared to larger fragments.