Meselson and Stahl

The Meselson-Stahl experiment demonstrated that DNA replication produces two DNA molecules each composed of

• Two old strands

• Two new strands

• One old strand and one new strand

• two strands with variable proportions of new and old DNA.

Starting with ¹⁵N¹⁵N (heavy) DNA, and after TWO generations in the ¹⁴N medium, Escherichia coli cells will contain

• 25% ¹⁵N¹⁵N DNA, 50% ¹⁵N¹⁴N DNA, and 25% ¹⁴N¹⁴N DNA.

• 50% ¹⁵N¹⁵N DNA and 50% ¹⁴N¹⁴N DNA.

• 50% ¹⁵N¹⁵N DNA and 50% ¹⁵N¹⁴N DNA.

• 50% ¹⁵N¹⁴N DNA and 50% ¹⁴N¹⁴N DNA.

• 25% ¹⁵N¹⁴N DNA and 75% ¹⁴N¹⁴N DNA.

Starting with ¹⁵N¹⁵N (heavy) DNA, and after THREE generations in the ¹⁴N medium, E. coli cells will produce the following band(s) in density-gradient centrifugation:

• a single band of DNA with medium density.

• one band of light DNA and one band of DNA with medium density.

• one band of heavy DNA and one band of DNA with medium density.

• one band of heavy DNA and one band of light DNA.

• three bands corresponding to DNA of light, medium and heavy density.

Meselson and Stahl performed the density-gradient centrifugation of DNA in a solution of calcium chloride.

• True

• False