When quantifying DNA, what does absorbance at 260 nm primarily reflect?

When quantifying DNA, what does absorbance at 260 nm primarily reflect?

• A. The amount of lipid
• B. The amount of nucleic acids
• C. The amount of protein
• D. The amount of carbohydrates

Answer: (B)

Nucleic acids are strong UV absorbers around 260 nm because their nucleotide bases have conjugated rings that absorb light in this region. Measuring absorbance at 260 nm lets you estimate how much DNA (or RNA) is present, since the absorbance scales with nucleic acid concentration via Beer-Lambert’s law. This wavelength is chosen because lipids, carbohydrates, and especially proteins contribute little at 260 nm, while proteins mainly absorb around 280 nm due to aromatic amino acids. A helpful check of sample quality is the 260/280 ratio, with pure DNA typically around 1.8.

Nucleic acids are strong UV absorbers around 260 nm because their nucleotide bases have conjugated rings that absorb light in this region. Measuring absorbance at 260 nm lets you estimate how much DNA (or RNA) is present, since the absorbance scales with nucleic acid concentration via Beer-Lambert’s law. This wavelength is chosen because lipids, carbohydrates, and especially proteins contribute little at 260 nm, while proteins mainly absorb around 280 nm due to aromatic amino acids. A helpful check of sample quality is the 260/280 ratio, with pure DNA typically around 1.8.