Question

A culture of E. coli growing in a medium containing a heavy isotope of nitrogen (¹⁵N) as the sole source of nitrogen is switched to a medium containing the normal, lighter isotope of nitrogen (¹⁴N) for 2 generations. What is the molar ratio of the hybrid DNA (¹⁵N-¹⁴N) to light DNA (¹⁴N-¹⁴N) at this point? Report your answer as a decimal to the nearest hundredths.

0.14 and 0.25 is not the answer

PLEASE EXPAIN IN DETAIL!!!!

Answer 1

All the DNA of E.Coli will contain N-15 initialy in N-15 medium. N-14 will be incorporated in the DNA When the Organism is shifted to N-14 medium. Hence the next generation will have one strand Containing N-15 And one strand containing N14. The ratio of N-14 to N-15 will be 1:1. In the next generation (Second from initial E. Coli) The new DNA strands will contain only N-14, But the parent will have one N-14 and one N-15 strand. Both N-14 and

N-15 will coil with new strands that contain N-14 strands only. So this generation will contain one N-15 strand for every three N-14 strands. Hence the ratio of N-15 to N-14 will be 1:3. (= 0.33)