14. DNA Synthesis

Meselson-Stahl Experiment

THE MOST BEAUTIFUL EXPERIMENT IN BIOLOGY: Meselson & Stahl, The Semi-Conservative Replication of DNA

Two stands composed of variable proportions of old and new DNA.

One old strand of DNA and one new strand of DNA.

The Meselson-Stahl experiment demonstrated that DNA replication produces new molecules of DNA each containing…

A cell containing a single chromosome is placed in a medium containing radioactive phosphate so that any new DNA strands formed by DNA replication will be radioactive. The cell replicates its DNA and divides. Then the daughter cells (still in the radioactive medium) replicate their DNA and divide, and a total of four cells are present. Sketch the DNA molecules in all four cells, showing a normal (nonradioactive) DNA strand as a solid line and a radioactive DNA strand as a dashed line.

E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment?
a. one high-density and one low-density band
b. one intermediate-density band
c. one high-density and one intermediate-density band
d. one low-density and one intermediate-density band

Trees can be killed by girdling—the removal of bark and vascular cambium in a ring all the way around the tree. Explain why.

Meselson and Stahl experiment

Meselson–Stahl Experiment

The DNA of a phage was injected into the bacterial host, but the protein coat remained outside. The viral DNA directed the host to replicate the new phage viruses. Which scientist(s) are associated with this finding?

Meselson and Stahl Experiment | Semi-Conservative Replication

Plants experience a vast array of conditions that can alter their growth and development, including temperature and availability of water, nutrients, and light. They are also exposed to pollutants such as acid rain formed largely as a result of burning fossil fuels and volcanic eruptions. Acid rain can strip minerals and nutrients from the soil, and eat away the outer waxy layer of tissue that protects a plant. Acid rain is still a major environmental problem in certain regions. How does acid rain affect plant growth?

Based on the results presented here, predict the impact of acid rain on the vascular cambium in the two species. How would that effect be apparent in the amount of wood produced in the tree trunks?

 No. This was known prior to the Meselson-Stahl experiments. 

 codes for the amino acid sequences of proteins 

 No. Meselson and Stahl did not show this. 

 replicates in a semiconservative fashion 

They used stable isotopes in their experiment.

The experiments of Meselson and Stahl showed that DNA __________.

Proof of Semi-Conservative DNA Replication: The 1958 Meselson-Stahl Experiment

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