What does an A260/A280 ratio of approximately 1.8–2.0 indicate for DNA?

What does an A260/A280 ratio of approximately 1.8–2.0 indicate for DNA?

• A. Pure DNA with minimal protein contamination
• B. DNA contaminated with RNA
• C. Pure RNA
• D. DNA completely free of salts

Answer: (A)

The A260/A280 ratio gauges nucleic acid purity by comparing how much light the sample absorbs at 260 nm (nucleic acids) to 280 nm (proteins). Pure DNA typically yields a ratio of about 1.8–2.0. When the ratio falls in this range, it suggests the sample is largely DNA with minimal protein contamination, since proteins absorb more at 280 nm and would lower the ratio. If proteins were present in significant amounts, the ratio would drop below 1.8. Conversely, a ratio around or above 2.0 often indicates RNA contamination, which increases absorbance at 260 nm relative to 280 nm, or other substances that affect the 260 nm absorbance. Salt alone doesn’t define this ratio, so it doesn’t indicate the sample is "completely free of salts." Therefore, a ratio of 1.8–2.0 best indicates pure DNA with minimal protein contamination.

The A260/A280 ratio gauges nucleic acid purity by comparing how much light the sample absorbs at 260 nm (nucleic acids) to 280 nm (proteins). Pure DNA typically yields a ratio of about 1.8–2.0. When the ratio falls in this range, it suggests the sample is largely DNA with minimal protein contamination, since proteins absorb more at 280 nm and would lower the ratio. If proteins were present in significant amounts, the ratio would drop below 1.8. Conversely, a ratio around or above 2.0 often indicates RNA contamination, which increases absorbance at 260 nm relative to 280 nm, or other substances that affect the 260 nm absorbance. Salt alone doesn’t define this ratio, so it doesn’t indicate the sample is "completely free of salts." Therefore, a ratio of 1.8–2.0 best indicates pure DNA with minimal protein contamination.