Question

1. to measure DNA concentration, if you take 1/10 of a sample and read the A260 and the reading is 1.5. what is the origin Dna concentration?

please show work!

Answer 1

Pure DNA solution usually has an OD₂₆₀/ OD₂₈₀ (Optical Density) ratio of alomst 1.8. Lower than this value indicates either protein or phenolic compound contamination and above this is indicative of RNA contamination. For spectrophotometric analysis, for a 1 cm pathlength of quartz cuvette, the OD at 260 nm (A₂₆₀) equals 1.0 for following solutions:

• 50 g/ mL solution of dsDNA
• 33 g/ mL solution of ssDNA

Since it's not mentioned whether the DNA solution is of dsDNA or ssDNA origin, both are calculated separately. The following formula is used to determine the original DNA concentration in a sample. The formula being:

dsDNA concentration= 50 g/ mL OD₂₆₀ dilution factor

= 50 g/ mL 1.5 10

= 0.05 mg/ mL 1.5 10

= 0.75 mg/ mL

ssDNA concentration= 33 g/ mL OD₂₆₀ dilution factor

= 33 g/ mL 1.5 10

= 0.03 mg/ mL 1.5 10

= 0.45 mg/ mL