If you diluted a stock solution of DNA 1/100, and then measured an A260 of 0.2, what was the initial concentration of the DNA stock? (give your numerical answer in μg/μl)

To determine the initial concentration of the DNA stock solution, we can use the following steps:

1. **A260 Reading**: The absorbance at 260 nm (A260) of 0.2 is given for the **diluted** DNA solution.
2. **Dilution Factor**: The DNA was diluted 1/100, meaning that the concentration of the DNA in the measured sample is 100 times lower than the stock solution.
3. **Concentration Calculation from A260**: A DNA solution with an A260 of 1 corresponds to a concentration of 50 µg/mL (or 0.05 µg/µL) for double-stranded DNA.

Let's calculate the concentration:

- Measured A260 = 0.2
- Concentration in the diluted sample = \( 0.2 \times 0.05 \, \text{µg/µL} = 0.01 \, \text{µg/µL} \)
  
Since the DNA was diluted 1/100, the stock solution concentration is:

\[
\text{Stock concentration} = 0.01 \, \text{µg/µL} \times 100 = 1 \, \text{µg/µL}
\]

Thus, the initial concentration of the DNA stock solution is **1 µg/µL**.

Would you like a detailed explanation of the concepts? 

Here are 5 follow-up questions for better understanding:
1. What is the significance of the A260 measurement in DNA concentration determination?
2. How does the dilution factor influence the concentration of the stock solution?
3. Why is the A260 value of 1 correlated with 50 µg/mL of double-stranded DNA?
4. How would the result differ if the dilution factor was 1/50 instead of 1/100?
5. What could cause deviations in the A260 readings in DNA concentration measurements?

**Tip:** Always ensure the DNA is free of contaminants like proteins or phenol that can affect the A260 reading.

Learn how to calculate the initial concentration of a DNA stock solution after a 1/100 dilution and A260 measurement of 0.2. This example covers key concepts in DNA quantification and dilution calculations. Suitable for undergraduate biology or biochemistry students.

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