Question

Meselson and Stahl allowed baclene raise in 13N medium to replicate in 14N medium. At the end of two rounds of DNA replication, they observed ______ band(s) in their centrifugation tubes which was/were composed of _______.

a. 1; single strands of 15N DNA base-paired to single strands of 14N DNA
b. 1; double strands of DNA each strand made up of a mixture of 14N and 15N DNA
c. double strands of 14N DNA at the top and double strands of 14N DNA at the bottom
d. 2; double strands of 14N DNA at the top and strands of 15N DNA base-paired to strands of 14N DNA in the middle
e. 2; strands of 15N DNA base-paired to strands of 14N DNA in the middle and double strands of 15N DNA at the bottom

Answer 1

Meselson and Stahl observed two bands in their centrifugation tubes after two rounds of DNA replication: one band composed of strands of 15N DNA base-paired to strands of 14N DNA in the middle, and another band of double strands of 14N DNA at the top. This supports the semiconservative replication model.

Step-by-step explanation:

Meselson and Stahl's experiment demonstrated that DNA replicates in a semi-conservative manner. After two rounds of DNA replication, they observed 2 bands in their centrifugation tubes: one band was composed of strands of 15N DNA base-paired to strands of 14N DNA in the middle, and the other band was double strands of 14N DNA at the top. This result supports the semiconservative replication model, where each strand of the DNA double helix serves as a template for the synthesis of a new complementary strand.