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TLS Online TPP Program

#Question id: 12570

Extinction is a natural phenomenon. It is estimated that 99% of all species that ever lived are now extinct. Why then do we say that we are now in a biodiversity crisis?

#Unit 10. Ecological Principles
  1. Humans are ethically responsible for protecting endangered species.
  2. Scientists have finally identified most of the species on earth and are thus able to Quantify the number of species becoming extinct.
  3. The current rate of extinction is high and human activities threaten biodiversity at all levels.
  4. Humans  have  greater  medical  needs  than  at  any  other  time  in  history,  and  many  potential  medicinal compounds are being lost as plant species become extinct.
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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?