Biology question - DNA sample

Question

You need to load 1 uL of a DNA sample onto an agarose gel. You have a tube of 6X loading dye you will use to make the sample sink into the well and be visible while it migrates. If you want to load this sample in a final volume of 10 uL, what will you add to the 1 uL of DNA? Important note: When given a concentration as an "X", you always assume the desired final concentration of this reagent is 1X unless otherwise indicated.

A. 1 uL of loading dye and 8 uL of water

B. 2 uL of loading dye and 8 uL of water

C. 1.7 uL of loading dye and 7.3 uL water

D. 1.8 uL of loading dye and 8.2 uL water

Answer 1

Hi Jas A.!

The question hints to us that we should consider the loading dye dilution. We are told the stock is a 6X preparation. Because we want to run the dye at a 1X concentration, we must dilute it. What we must do is figure how much, or what volume, of the stock we need for our 10μL sample volume. For this, we can use the dilution equation:

M₁V₁ = M₂V₂ => V₁ = M₂V₂/M₁

V₁ represents the volume of our stock concentration that we will need.

V₁ = M₂V₂/M₁

<=> (1X*10μL)/6X

V₁ = 1.7μL of loading dye

Please note that we can use any units for both the concentration and volume variables. We need not adhere to simply using molarity and liters, so long as we are consistent in our problem. For instance, you must use mL for V₂ if you also used mL for V₁. You cannot use mL for V₂ if you used μL for V₁.

To find the volume of water for the proper dilution, we simply subtract:

V_sample + V_dye + V_H2O = V_total => V_H2O = V_total - (V_sample + V_dye)

<=> 10μL - (1μL + 1.7μL)

V_H2O = 7.3μL

It is noteworthy that running multiples of 6μL would be ideal with such a stock concentration.

Hope this helps!

Cheers