Assume that you grew a culture of E. coli for many generations in medium containing 15N (from the ammonium ion), a heavy isotope of nitrogen. You extract DNA from a portion of the culture and determine its density to be 1.723 gm/cm3 (call this sample A). You then wash the remaining E. coli cells, grow them for one generation in 14N, and extract the DNA from a portion of the culture (call this sample B). You let the culture grow for one more generation in 14N and extract the DNA (call this sample C). Each sample of DNA (A, B, and C) is then subjected to ultracentrifugation. Present the centrifugation profiles that you would expect under (a) semiconservative replication and (b) conservative replication. (Note: Assume that unlabeled [14N] DNA has a density of 1.700 gm/cm3.)
The process of plant tissue culture.
Alternation of generations, the plant life cycle
E.COLI
Creede, Colorado, circa 1890, a rough silver mining town that grew from 660 people in 1889 to over 1
Structure of E. coli 30S pre-rRNA