Meselson and Stahl IB Bio

DNA replication was proved by the experiments of:

• Hershey & Chase
• Meselson & Stahl
• Watson & Crick
• Franklin & Gosling

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.

Which model does NOT predict that after one replication both DNA molecules will be a 50/50 mix of original and new DNA?

• conservative

• semi-conservative

• dispersive

In the Meselson-Stahl experiment, E.coli was transfered from ¹⁵N medium to ¹⁴N medium. Centrifugation of DNA after 20 minutes in ¹⁴N produced ____ and disproved the ____ model.

• 1 intermediate band, conservative

• 1 intermediate band, dispersive

• 1 heavy band and 1 light band, semi-conservative

• 1 light and 1 intermediate band, dispersive

Tags

NGSS.HS-LS3-2

In the Meselson-Stahl experiment, E.coli was transfered into ¹⁴N medium from ¹⁵N medium. The bacteria is incubated and reproduced up to 2 generation of offsprings. Centrifugation of DNA after 40 minutes in ¹⁴N produced ____ and disproved the ____ model.

• 1 light and 1 intermediate band, dispersive

• 1 light and 1 intermediate band, conservative

• 1 intermediate band, dispersive

• 1 heavy and 1 light band, semi-conservative

What is the end result of DNA replication?

• 2 semi-conservative strands of DNA

• 1 semi-conservative strand of DNA

• Half of a semi-conservative strand.

• Nothing is created

This is the correct model for DNA Replication.

• True

• False

This is the correct model for DNA Replication.

• True

• False