Question

Which of the following formulae may be used to estimate the concentration of RNA by UV spectrophotometer

• A. $40 \times A_{260}$
• B. $50 \times A_{260}$
• C. $40 \times A_{280}$
• D. $50 \times A_{280}$

Hint:

Remember the calibration values:
- RNA $\rightarrow 40 \times A_{260}$
- dsDNA $\rightarrow 50 \times A_{260}$

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Purines and pyrimidines in nucleic acids absorb ultraviolet (UV) light, with a peak absorbance near $260 \text{ nm}$. This property is used to quantify DNA and RNA concentrations in solution.
Key Formula or Approach:
The concentration of single-stranded RNA is calculated using Beer-Lambert's Law, where a standard calibration constant relates absorbance ($A_{260}$) to concentration: \[ \text{Concentration of RNA } (\mu\text{g/mL}) = A_{260} \times \text{Dilution Factor} \times 40 \]

Step 2: Detailed Explanation:
- By biophysical standard, an optical density (OD) or absorbance of $1.0$ at a wavelength of $260 \text{ nm}$ ($A_{260} = 1.0$) in a $1\text{ cm}$ pathlength quartz cuvette corresponds to:
- $40 \ \mu\text{g/mL$} of single-stranded RNA.
- $50 \ \mu\text{g/mL$} of double-stranded DNA.
- $33 \ \mu\text{g/mL$} of single-stranded synthetic oligonucleotides.
- Therefore, the formula to find the concentration of RNA ($\mu\text{g/mL}$) from an absorbance reading is $40 \times A_{260}$ (assuming no dilution).

Step 3: Final Answer:
The formula used to estimate RNA concentration is $40 \times A_{260}$.