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 percent, 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.
(a) approximately 1.712
(b) 1.723 and 1.700
(c) thymine = 20%, guanine = 30%, cytosine = 30%
(d)
You might also like to view...
In a growing population, the youngest age classes have
A. the highest number of deaths/year. B. the fewest individuals. C. the most individuals. D. the smallest number of deaths/year. E. the most individuals and the largest number of deaths/year.
In a heterozygote for two linked genes, both dominant alleles are on one chromosome and both recessive alleles are on another chromosome. The genes are said to be in
A) recombination. B) repulsion. C) cis. D) trans.
Experiments conducted in the 1920s by Frederick Griffith involving the bacterium Diplococcus pneumoniae demonstrated that a substance from one bacterial strain could genetically transform other bacterial strains
What was the name of the substance capable of such transformation, and who finally determined its identity?
Mobile genetic elements that are permanently integrated into a microbial genome are known as ________ ________.
Fill in the blank(s) with the appropriate word(s).