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TLS Online TPP Program

#Question id: 12755

Which of the following statements best describes why biologists are currently concerned with global warming and the thawing of permafrost in many areas of the tundra biome?

#Unit 10. Ecological Principles
  1. The thawing process will likely decrease the abundance and diversity of soil-dwelling organisms in tundra habitats.
  2. The bacterial decomposition of  the thawed organic materials on  the widespread areas of  the tundra will produce large quantities of CO2, which will add to greenhouse gases and exacerbate global warming.
  3. Oil and coal deposits will thaw and rise to the surface (because of their lower density) of the tundra, destroying millions of acres of arctic habitat.
  4. Populations of humans inhabiting the arctic will have to move to more southern latitudes, resulting in in- creased competition for resources in already densely populated areas.
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TLS Online TPP Program

#Question id: 3816

#Unit 3. Fundamental Processes

The mechanism of DNA replication is studied in an E. coli replication fork. Which is a characteristic of an E. coli replication fork and a eukaryotic replication fork?
TLS Online TPP Program

#Question id: 3817

#Unit 3. Fundamental Processes

DNA replication is studied in a newly discovered bacterium. It takes 30 min for the bacterium to complete a round of replication at 37oC. A Meselson-Stahl-type experiment was performed. The bacteria were grown for several generations in 14N-medium and then switched to 15N-medium. The DNA molecules were then analyzed.

If the mechanism of DNA replication in this bacterium were dispersive, what results would be found when the double-stranded DNA was analyzed in a CsCl gradient after two generations in 15N-medium?
TLS Online TPP Program

#Question id: 3818

#Unit 3. Fundamental Processes

DNA replication is studied in a newly discovered bacterium. It takes 30 min for the bacterium to complete a round of replication at 37oC. A Meselson-Stahl-type experiment was performed. The bacteria were grown for several generations in 14N-medium and then switched to 15N-medium. The DNA molecules were then analyzed.

If the mechanism of DNA replication in this bacterium were semi-conservative, what results would be found when the double-stranded DNA was analyzed in a CsCl density gradient after three generations in 15N-medium?
TLS Online TPP Program

#Question id: 3819

#Unit 3. Fundamental Processes

DNA replication is studied in a newly discovered bacterium. It takes 30 min for the bacterium to complete a round of replication at 37oC. A Meselson-Stahl-type experiment was performed. The bacteria were grown for several generations in 14N-medium and then switched to 15N-medium. The DNA molecules were then analyzed.

After one generation in 15N-medium, the DNA is denatured and analyzed in a CsCl gradient. If the single-stranded DNA forms two bands, one with heavy density and one with light density, what conclusion could be drawn about the mechanism of DNA replication in this bacterium?
TLS Online TPP Program

#Question id: 3820

#Unit 3. Fundamental Processes

Meselson and Stahlʹs experiments involved growing E. coli on a medium containing 15N (heavy nitrogen) which increased the density of the bacterial DNA. Cells were then grown on a medium containing only 14N. DNA samples were obtained for analysis after one, two and three rounds of replication (generations) and centrifuged on a density gradient. The double-helical DNA forms bands in the gradient depending on its density. How many bands did Meselson and Stahl see after two generation of cells were grown on the 14N medium?
TLS Online TPP Program

#Question id: 3821

#Unit 3. Fundamental Processes

Which mechanism contributes to accuracy during DNA replication?