We have examined two physiological extremes with respect to concentration – how

Question

We have examined two physiological extremes with respect to concentration – how low levels of hormones amplify their signal, and the incredible compaction of DNA to fit 2 m of DNA into the nucleus of a single cell. In order to better appreciate and contrast these extremes answer the following questions:

A. Epinephrine, C9H13NO3, has a concentration of 10-10 M in circulating blood. Calculate the diameter of a round swimming pool with a water depth of 2.0 M that would be needed to dissolve 1.0 g (about a teaspoon) of epinephrine to a concentration equal to that in the blood?

B. Assuming the human genome has equal concentrations of each of the four nucleotides, what is the approximate mass of nucleotides that one would have to add to this pool to provide a concentration in the pool equivalent to the concentration of nucleotides in chromosomal DNA in the human nucleus of a typical cell?

I need help solving B. I am unsure how to relate the length of DNA in the question stem (2.0 meters) to solve the nucleotide masses (relating length to concentration).

Explanation / Answer

Human genome contains 3.2 × 109 nucleotides and is distributed over 24 different chromosomes. (A= 313.21, T= 304.2, C= 289.18, G=329.21)

DNA nucleotide = 325 Daltons

MW of a ssDNA molecule= (number of bp) x (325 Daltons/per base)

Moles of a ssDNA molecule = (grams of DNA)/ (MW in Daltons)

Average weight of a DNA basepair = 65 daltons (1 dalton equals the mass of a single hydrogen atom, 1.67 x 10-24grams)

Molecular weight of a ds DNA molecule = (number of basepairs x 650 daltons)

Total weight of the human genome = 3.3 x 109

bp x 650Da = 2.15 X 1012 Da.

One dalton is 1.67 x 10-24grams, so the human genome weighs 3.59 x 10-12 grams (10-12 grams is also known as a picogram).

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