Question

1. What is the purpose of the sample buffer? 2. What would happen if you did not add the sample buffer before loading your DNA sample on the gel? 3. What is the purpose of the blue dye?

Answer 1

1. Sample buffer contains glycerol, xylene cyanol and bromophenol blue. It provides three important functions.

i. It provides density to the sample

ii. It helps in monitoring the gel running status

iii. If the sample volume is too low (Ex: 1uL or 0.5 uL), we can dilute it with the sample buffer so that it can be easily loaded into the gel lane.

2. If the DNA is not mixed with sample buffer,

i. The DNA would get diffused into the tank buffer/gel. SO, we can not observe/obtain crisp bands (The quantity also gets reduced as some sample diffuses out).

ii. We can not monitor the gel running status.

3. The blue dye runs at ~50 bp region. So, we can approximately guess the position of our interested DNA bragment on the gel using the blue dye as a control.

The xylene cyanol band (Light green/blusih green) runs approximately at 3kb.