Question

In gel electrophoresis, DNA fragments move across a gel. When voltage is applied to the gel, which end of the gel becomes positively charged?

1) The positive end
2) The negative end
3) Both ends
4) None of the above

Answer 1

In gel electrophoresis, DNA fragments with a negative charge migrate towards the positively charged end of the gel when an electric voltage is applied. Because DNA is attracted to the positive electrode, when voltage is applied to the gel, the end that becomes positively charged is known as the positive end. Hence, option (1) is correct.

Step-by-step explanation:

In gel electrophoresis, an electric field is applied across a gel matrix to separate DNA fragments based on size and charge. DNA molecules possess a net negative charge due to the phosphate groups in the DNA backbone.

Thus, when voltage is applied during gel electrophoresis, the DNA fragments move from the negative electrode towards the positive electrode, which becomes positively charged. The opposite end of the gel, where the DNA samples are loaded, is the negative electrode. Due to the DNA's negative charge, smaller DNA fragments move faster and farther towards the positively charged end as compared to larger ones.

After the separation process, the DNA fragments are visualized with a fluorescent dye like ethidium bromide.