Matthew Meselson and Franklin Stahl demonstrated that DNA replication is semicon
ID: 204535 • Letter: M
Question
Matthew Meselson and Franklin Stahl demonstrated that DNA replication is semiconservative in bacteria.
Choose the correct description of their experiment.
A.
Meselson and Stahl initially cultured E. coli in medium containing only 15N until all cells contained only 15N/15N DNA. They then cultured the 15N/15N E. coli in normal medium (14N) and collected samples after one, two, and three rounds of DNA replication.
B.
Meselson and Stahl initially cultured E. coli in medium containing both 14N and 15N until all cells contained only 14N/15N DNA. They then cultured the 14N/15N E. coli in normal medium (14N) and collected samples after one, two, and three rounds of DNA replication.
C.
Meselson and Stahl initially cultured E. coli in medium containing both 14N and 15N until all cells contained only 14N/15N DNA. They then cultured the 14N/15N E. coli in medium containing only heavy nitrogen (15N) and collected samples after one, two, and three rounds of DNA replication.
D.
Meselson and Stahl initially cultured E. coli in medium containing only 15N until all cells contained only 15N/15N DNA. They then cultured the 15N/15N E. coli in medium containing both 14N and 15N and collected samples after one, two, and three rounds of DNA replication.
A.
Meselson and Stahl initially cultured E. coli in medium containing only 15N until all cells contained only 15N/15N DNA. They then cultured the 15N/15N E. coli in normal medium (14N) and collected samples after one, two, and three rounds of DNA replication.
B.
Meselson and Stahl initially cultured E. coli in medium containing both 14N and 15N until all cells contained only 14N/15N DNA. They then cultured the 14N/15N E. coli in normal medium (14N) and collected samples after one, two, and three rounds of DNA replication.
C.
Meselson and Stahl initially cultured E. coli in medium containing both 14N and 15N until all cells contained only 14N/15N DNA. They then cultured the 14N/15N E. coli in medium containing only heavy nitrogen (15N) and collected samples after one, two, and three rounds of DNA replication.
D.
Meselson and Stahl initially cultured E. coli in medium containing only 15N until all cells contained only 15N/15N DNA. They then cultured the 15N/15N E. coli in medium containing both 14N and 15N and collected samples after one, two, and three rounds of DNA replication.
Explanation / Answer
Option A is correct.
Meselson and Stahl initially cultured E. coli in medium containing only 15N until all cells contained only 15N/15N DNA. They then cultured the 15N/15N E. coli in normal medium (14N) and collected samples after one, two, and three rounds of DNA replication. Meselson and Stahl used E.coli as model organism fro their experiment. They began by growing E. coli in medium, or nutrient broth, containing a "heavy" isotope of nitrogen, 15N. When grown on medium containing heavy 15N, the bacteria took up the nitrogen and used it to synthesize new biological molecules, including DNA. After many generations growing in the 15N medium, the nitrogenous bases of the bacteria's DNA were all labeled with heavy. Then, the bacteria were switched to medium containing a "light" 14N isotope and allowed to grow for several generations. Meselson and Stahl knew how often E. coli cells divided, so they were able to collect small samples in each generation and extract and purify the DNA.