Gel Electrophoresis

RELEVANT LEARNING OUTCOME:

(a) Describe the principles and procedures of these molecular techniques:

b. gel electrophoresis; and

🕐Estimated time for this section: 25 minutes

Gel Electrophoresis

A method of separating DNA, RNA or protein based on the rate of movement in a liquid medium under the influence of an electric field.

Gel Electrophoresis set up

Diagram on the left shows an agarose gel electrophoresis set up. The agarose gel sits in a tank of buffer, the samples mixed with loading dye are placed in wells at one end of the gel and an electrical current is applied causing the negatively charged DNA to move towards the positive electrode (anode). Credit: Technology Networks.

Procedure of gel electrophoresis

Step I: Preparation of agarose gel (A-D)

Step II: Adding of loading dye into sample

Step III: Adding of loading dye (E)

Step IV: Running of sample

The negatively-charged DNA will migrate towards the postive electrode (anode) which is usually colored red.

Step V: visualising the samples

A) Depicts the typical result of DNA electrophoresis. On the left, there is a size marker/DNA ladder that is used as a reference for the length of the sample DNA fragments. To the right of the marker are three samples: Sample A, B and C. The image shows how smaller DNA fragments move further through the agarose gel than the larger fragments of DNA.

B) The graph shows the nonlinear, relationship between the size of the DNA fragments and the distance migrated. It is a negative curve, and as DNA fragments get larger, they migrate less distance through the gel.

Credit: Mckenzielower, reproduced under the Creative Commons Attribution-Share Alike 4.0 International license.

Gel Electrophoresis Animation

👁️‍🗨️Watch the animation to learn more about the steps involved in the gel electrophoresis.

Questions:

Why do DNA fragments move through the gel when an electric current is applied, and toward which electrode do they travel?
Why is a DNA ladder (marker) included alongside sample lanes, and how does it help interpret the results?
What is the purpose of the wells in the gel and why must DNA samples be loaded into them before running the electric current?

How to load and run DNA samples in the lab?

👁️‍🗨️Prepare yourself for practical session by watching this video that demonstrates how to load and run DNA samples on an agarose gel.

🖊️Check Your Understanding: Learning Goals

Attempt Qn 7-14 of the Molecular techniques Learning Goals