Figure 13.1
-A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in Figure 13.1 would you expect if the DNA was replicated in a conservative manner?
A) A
B) B
C) C
D) D
E) E

Question

Figure 13.1
-A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in Figure 13.1 would you expect if the DNA was replicated in a conservative manner?
A) A 
B) B 
C) C 
D) D 
E) E

Quizplus · Accepted Answer

If DNA replication occurs in a conservative manner, the parental double-stranded DNA helix remains intact, and the newly synthesized complementary DNA strands form a new helix. This results in one daughter DNA molecule with both strands composed of newly synthesized DNA and the other daughter molecule with both strands composed of the parental DNA. This would result in a pattern like B, where the band positions switch from heavy to light and back to heavy again.

Figure 13.1 -A Space Probe Returns with a Culture of a Microorganism