Question 1

DNA is extracted from a suspect's blood by phenol/chloroform to determine if he was involved in a murder case. Thirty µL of the purified DNA is diluted in 970 µL of water (for a final volume of 1000 µL). That dilution is put into a quartz cuvette and its absorbance is read on a spectrophotometer at 260 nm. It gives a reading of 0.25. What is the concentration of DNA in the original sample? (phenol/chloroform extraction results in double stranded DNA use 50 ug DNA / mL = 1 O.D. to calculate concentration)

Accepted Answer

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Question 2

A reference sample is needed from a victim of a sexual assault. Cells are recovered from a saline mouthwash procedure and the DNA is isolated by Chelex extraction. The DNA is diluted 40 µL into a total volume of 1000 µL and its absorbance is measured on a spectrophotometer at 260 nm. It gives a reading of 0.20. What is the concentration of DNA in the reference sample? (Chelex extraction renders DNA in a single stranded form, use 33 ug DNA / mL = 1 O.D. to calculate concentration)

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Question 3

Ten µL of a suspect's reference DNA sample is diluted into 990 µL of water and its absorbance is read on a spectrophotometer. It gives an absorbance of 0.41 at 260 nm and an absorbance of 0.32 at 280 nm. What is its 260/280 ratio?

Accepted Answer

The answer of Ten µL of a suspect's reference DNA...

Question 4

If you recover 4000 cells from a saline mouthwash, how many µg of genomic DNA does that represent? [To solve this problem, you need to know that there are approximately 6 x 10⁹ bp of DNA per cell, that one mole of base pairs weighs 660 grams, that there are 1 x 10¹² pg/g, and that one mole of anything is 6.023 x 10²³ (Avogadro's number) of that thing.]

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Question 5

What percent of your body weight is made up of DNA? Assume that your body consists of 1x10¹⁴ cells. (1 lb = 453.6 g)

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Quiz 5: Dna Quantitation

Ten µL of a suspect's reference DNA sample is diluted into 990 µL of water and its absorbance is read on a spectrophotometer. It gives an absorbance of 0.41 at 260 nm and an absorbance of 0.32 at 280 nm. What is its 260/280 ratio?

What percent of your body weight is made up of DNA? Assume that your body consists of 1x1014 cells. (1 lb = 453.6 g)

What percent of your body weight is made up of DNA? Assume that your body consists of 1x10¹⁴ cells. (1 lb = 453.6 g)