Meselson and Stahl Experiment Analysis

The Meselson-Stahl experiment demonstrated the semi-conservative replication of DNA. Bacterial cells were grown in a medium with heavy nitrogen (N15) and then transferred to a medium with lighter nitrogen (N14). DNA was extracted and centrifuged in cesium chloride, forming a density gradient. After one generation, DNA showed an intermediate density, indicating semi-conservative replication. After two generations, two bands appeared, confirming the model. The experiment concluded that DNA replication involves separating parent strands and synthesizing new complementary strands.

What does the Meselson and Stahl experiment provide evidence for?

• Conservative replication

• Dispersive replication

• Semi-conservative replication

• Random replication

In the experiment, what type of nitrogen isotope was initially used to grow the bacterial cells?

• N16

• N17

• N15

• N14

What was the purpose of transferring the bacterial cells to a medium containing N14?

• To change the bacterial species

• To observe the replication process

• To stop the experiment

• To increase the growth rate

What solution was used to dissolve the extracted DNA?

• Potassium chloride

• Sodium chloride

• Cesium chloride

• Magnesium chloride

What happens to DNA molecules during cesium chloride centrifugation?

• They dissolve completely

• They move to a position where their density equals that of the cesium

• They break into smaller pieces

• They change their chemical structure

After one generation in N14 medium, what was observed about the DNA band?

• It had the same density as N15 DNA

• It had the same density as N14 DNA

• It had a density between N14 and N15 DNA

• It disappeared completely

What did the single band of DNA after one generation in N14 medium indicate?

• Neither strand contained N15

• One strand contained N15 and the other N14

• Both strands contained N14

• Both strands contained N15

After two generations in N14 medium, how many DNA bands were observed?

• Four

• Three

• Two

• One

What did the two bands observed after two generations in N14 medium represent?

• One band had intermediate density and the other had low density

• Both bands had intermediate density

• Both bands contained N14

• Both bands contained N15

What conclusion did Meselson and Stahl draw from their experiment?

• DNA replication is conservative

• DNA replication is random

• DNA replication is semi-conservative

• DNA replication is dispersive