Question

Quantification of DNA Using Agarose Gels

Directions: Please answer the following questions in complete sentences.

What problems might arise if the agarose wasn't dissolved/melted completely or if there were air bubbles in the gel?

Why did your DNA samples need to be mixed with a loading dye prior to loading the samples into the gel? Give 2 reasons.

What causes the DNA to travel through the gel?

Draw a sketch of what your gel would have looked like (after 5 minutes) if you reversed the positive and negative leads and placed the positive lead closest to the wells. Label the positive and negative leads, the wells, and the DNA.

Why do smaller DNA fragments travel further down the gel?

Answer 1

1. If the agarose wasn't dissolved or melted completely or it has a bubble the loaded sample won't move further down.

2. DNA samples need to be mixed with a loading dye prior to loading the samples into gel because it gives some weight to the DNA sample so that it sinks down into the well of the agarose gel. It also helps in visual tracking of the sample in the gel.

3. The charge present on the DNA helps it travel through the gel. DNA is negatively charged which helps the DNA to move towards the positive charge in an electrophoresis.

4. If we reversers positive and negative leads and place the positive lead closet to the wells, the DNA will move in an opposite direction. In other words it will move up instead of moving down. If we keep it for longer duration it might come out into the tank.

5. Smaller DNA fragments travel further down the gel because of its small size. When the concentration of agarose gel is high smaller sized DNA moves fast.