What does OD600 measure?

What does OD600 measure?

• A. Optical density at 600 nm; a proxy for cell density in a liquid culture.
• B. Absolute concentration of DNA.
• C. pH of the culture.
• D. Temperature of the incubator.

Answer: (A)

OD600 is a measure of how turbid a liquid culture is by shining light at 600 nm and detecting how much passes through. The more cells present, the more light is scattered and absorbed, so less light reaches the detector and the optical density increases. This relationship lets you estimate cell density quickly without destroying the culture, and it’s commonly used to monitor growth curves or to standardize inoculations. It’s not a direct measure of DNA, pH, or temperature. DNA concentration is assessed with methods that target nucleic acids (often using absorbance at 260 nm or DNA-specific assays). pH is read with a pH meter or indicator dyes, and temperature is measured with a thermometer or probe. Keep in mind that OD600 reflects turbidity from all cells (live and dead) and has a usable linear range, so very high densities may require dilution for accurate readings.

OD600 is a measure of how turbid a liquid culture is by shining light at 600 nm and detecting how much passes through. The more cells present, the more light is scattered and absorbed, so less light reaches the detector and the optical density increases. This relationship lets you estimate cell density quickly without destroying the culture, and it’s commonly used to monitor growth curves or to standardize inoculations.

It’s not a direct measure of DNA, pH, or temperature. DNA concentration is assessed with methods that target nucleic acids (often using absorbance at 260 nm or DNA-specific assays). pH is read with a pH meter or indicator dyes, and temperature is measured with a thermometer or probe. Keep in mind that OD600 reflects turbidity from all cells (live and dead) and has a usable linear range, so very high densities may require dilution for accurate readings.