Assume That a Culture of E

question 45

Essay

Assume that a culture of E.coli was grown for approximately 50 generations in ¹⁵N (provided in the medium in the ammonium ion),which is a heavy isotope of nitrogen (¹⁴N).You extract the DNA from the culture,and it has a density of 1.723 gm/cm³ (water = 1.00 gm/cm³).From the literature,you determine that DNA containing only the common form of nitrogen,¹⁴N,has a density of 1.700 gm/cm³.Bacteria from the ¹⁵N culture were washed in buffer and transferred to ¹⁴N medium for one generation immediately after which the DNA was extracted and its density determined.
(a) What would be the expected density of the extracted DNA?
(b) After you heat the extracted DNA until it completely denatures (95°C for 15 minutes),what would you expect the density of the DNA in the denatured extract to be? For the purposes of this question,assume that DNA has the same density regardless of whether it is single- or double-stranded.
(c) Assuming that the molar percentage of adenine in the extracted DNA was 20%,what would be the expected molar percentages of the other nitrogenous bases in this DNA?
(d) Assume that a fraction of the extracted DNA was digested to completion with the enzyme snake venom diesterase.This enzyme cleaves between the phosphate and the 3′ carbon.Present a "simplified" diagram that would illustrate the structure of the predominant resulting molecule.

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Definitions:

Homogeneous Product

A product that is uniform in quality and indistinguishable from other products of the same type.

Weighted-Average Method

A process costing method that calculates unit costs by combining costs and outputs from the current and prior periods.

Prior Period Costs

Costs that were incurred in a previous accounting period but are recorded or recognized in the current period's financial statements.

Processing Costing System

An accounting system used to allocate production costs to products or services when they are mass-produced in continuous processes.