CfE Higher Sht1_1A
HBiol Sheet 1_1A
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1. The diagram below shows part of a DNA molecule.
a) Name components X and Y.
b) Name the type of bond shown at Z.
2. The diagram below summarises the original experiment performed by Griffiths to investigate the molecules which carry information. The rough strain (R) of pneumococcus bacteria is non-virulent, but the smooth strain (S) is lethal. An interactive animation has been prepared detailing the experimental method. This will help you answer some of the questions that follow. Click on the diagram below to access the interactive presentation.
Griffiths concluded from his experiments that a transforming principle was responsible for the passage of virulence. Avery et.al. subsequently isolated this transforming principle. In their experiments they separated a lysate, containing the transforming principle from other cell debris. They used different enzyme treatments to determine which of the components of the lysate were responsible for the transformation of the R into S strain.
Answer the following questions:
a) What is the structural difference between the rough and smooth strains of pneumococcus?
b) How might they have separated the lysate from the cell debris?
c) Separate samples of the lysate were treated with different enzymes. Why would the use of enzymes allow the scientists to determine which of the components was responsible for the transformation?
d) Explain why the treatment of the lysate with enzyme SIII failed to prevent the lysate from transforming the R strain into virulent S train bacteria.
e) Avery et. al. used alcohol to isolate the nucleic acids. How did they manage to distinguish between the role of DNA and RNA?
f) What did Avery et.al. conclude from their experiments?
g) Bacteria can exchange DNA naturally. What structure in a bacterium allows them to exchange DNA?
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