Question

Meselson and Stahl’s work on DNA replication takes an experimental approach, where some cells are grown in culture in the presence of radioactive nucleotides for many generations so that both strands of every DNA molecule include radioactive nucleotides. The cells are then harvested and placed in new medium with nucleotides that are not radioactive so that newly synthesized DNA will not be radioactive. _______ (proportion) of DNA molecules (each molecule is double stranded not single stranded) will contain any radioactivity after two rounds of replication? This experiment also demonstrates that replication is__________________.

a. 1/8; semiconservative
b. 1/8; dispersive
c. 1/4; conservative
d. 1/2; conservative
e. 1/2; semiconservative

Answer 1

Option E 1/2 semiconservative

Step-by-step explanation:

Typically, after the first round of replication, their experiments should yield 2 molecules of double stranded DNA, for one molecule of DNA that is double stranded; one parental radioactive strand and a new non-radioactive strand.

Then, after two rounds of replication, there should be 2 molecules of double stranded DNA with this characteristic and another two with a completely non-radioactive double stranded DNA.

Thus, 2/4=1/2 proportion of DNA molecule will not contain any radioactivity and this type of replication is semi conservative.

Answer 2

e. 1/2; semiconservative

Step-by-step explanation:

1/2 (proportion) of DNA molecules (each molecule is double stranded not single stranded) will contain any radioactivity after two rounds of replication.

This experiment also demonstrates that replication is semiconservative .

DNA replication is semi-conservative because each helix that is created contains, one strand from the helix from which it was copied.