Practice question

Spectrophotometric purity ratio A260/A280 assesses protein contamination in nucleic acid preparations. Nucleic acids absorb maximally at 260 nm, proteins due to aromatic residues absorb at 280 nm. Pure DNA shows ratio about 1.8, pure RNA about 2.0. If ratio is below 1.8 for DNA, it indicates excess absorbance at 280 nm contributed by residual proteins, phenol, or other contaminants absorbing near 280 nm. Ratios below threshold suggest inadequate deproteinization by phenol or protease. Pure RNA would show higher ratio, while pure DNA falls below that threshold.