Discussion Questions - Answers
Gel Electrophoresis | Multimedia | Activities
Gel Electrophoresis - Activity 3 - Discussion Questions - Answers/Teacher Guide
Gel Electrophoresis - Activity 3 - Discussion Questions - Answers/Teacher Guide
Why do we cut up the DNA before running it on the gel?
When DNA is in one long strand, it forms a continuous blur on the gel. The use of restriction enzymes to cut up the DNA allows different size segments to separate in the gel.
What is the purpose of the dye?
Since DNA is not visible without UV light, the dye is used to check how close the DNA is to the end of the gel. The DNA should not run off the gel, but DNA moves slower than the dye. When the dye is close to the end of the gel, power is turned off so the gel is stopped.
Why is it important to have clear bands on the gel?
The clearer the bands, the more accurate the gel is, and the better the individual strands have separated. Messy, blob-like bands indicate long strands of DNA, or contamination of the DNA with proteins.
Why do we use a buffer, not just water or air?
The buffer allows electrical current to flow through the gel, which is what causes the DNA to move. Water and air do not conduct the current as well as the buffer.
What happens when the voltage is turned up on the machine?
The higher the voltage, the more
What happens if more agarose were added to the gel initially?
When more agarose is added, the holes the DNA travels through is smaller. If most of the pieces of DNA you are electrophoresing are small, then the gel will be clearer with more agarose added. This is called increasing the resolving power of the gel.
Is DNA positively charged or negatively charged? How does this effect gel electrophoresis?
Because of the phosphates linking the sugars in the backbone, DNA is negatively charged. In gel electrophoresis, the DNA moves towards the positive electrode. If the gel is set up backwards, the DNA quickly runs out of the loading wells and into the surrounding buffer.
Besides forensics, can you think of any other uses of gel electrophoresis?
Locating genes, sequencing DNA, isolating and extracting a certain size DNA piece