Practice question

Nucleic acid purity is assessed by spectrophotometry at 260 nm for nucleic acids and 280 nm for aromatic amino acids in proteins. Pure DNA has an A260/A280 ratio of approximately 1.8, due to lower absorption of pure DNA at 280 nm. A ratio significantly lower than 1.8 indicates protein contamination because proteins absorb strongly at 280 nm. A ratio around 2.0 indicates pure RNA. Reagent contamination like phenol absorbs at 270 nm and affects A260/A230. Thus 1.8 is a standard indicator of protein-free DNA suitable for molecular applications.