Biology 12

Chapter 7 Nucleic Acids: The Molecular Basis of Life • MHR 231

SECTION REVIEW

1. Describe the observations made by Franklin
   that proved to be keys to understanding the
   molecular structure of DNA.


2. Describe the evidence that led Watson and
   Crick to their particular model of DNA.


3. DNA is a large double helix, resembling a
   twisted ladder. Describe the component molecules
   that make up the ladder uprights and the pattern of
   their arrangement.


4. Create a chart that compares and contrasts the
   similarities and differences in the structure of DNA
   and RNA.


5. The four nitrogenous bases are paired to make
   up the rungs of the DNA ladder. Differentiate between
   the purine and pyrimidine structures of each of these
   nitrogenous bases, and explain the significance of the
   pattern of their arrangement.


6. Watson and Crick concluded that DNA
   consisted of two individual strands arranged in
   antiparallel directions. Explain the significance of
   this arrangement.


7. Identify and describe the three different kinds of
   forces that contribute to the molecular stability of the
   DNA molecule.


8. Describe the organization of genetic material in
   prokaryotic organisms. What purpose is served by
   having DNA incorporated into plasmids?
   9. Describe the organization of DNA in eukaryotic
   organisms. What is the reason for the compact
   nature of chromosomes?


9. Scientists have extracted DNA from the different
   types of cells within one species and from the same
   kinds of cells among many different species. Decide
   whether the results from this research alone will or
   will not support the hypothesis that DNA is the
   genetic material. Justify your decision.


10. DNA is a doubled-stranded helical molecule.
    RNA is a single-stranded molecule. Based on the
    structural characteristics of each molecule, determine
    which is more efficient at coding genetic information.


11. Should scientists be compelled to share
    information out of a spirit of fairness? Linus Pauling
    was one of the favoured competitors in the race to
    discover the molecular structure of DNA, due to his
    superior knowledge of organic chemistry. However,
    Watson and Crick, who had access to Franklin and
    Wilkins’ X-ray pictures and knowledge of Pauling’s
    theories from his son, claimed the victory. Based on
    your independent review of the history of this event,
    how do you think the race might have ended differently?

Start gathering statistics on the type of cancer you have

chosen to study. Who is most likely to be affected by this

cancer?

UNIT PROJECT PREP

MC

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I

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C

C

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Figure 7.19The total length of the DNA in a single human
chromosome reaches approximately 10 cm. The successive
ordering of genetic material begins with the formation of
nucleosomes (A) and culminates with the condensed
chromosome (B), shown here as a pair of sister chromatids

during mitosis. This ordering compacts the DNA by a factor

of tens of thousands — the equivalent of coiling 50 km

of thread into a piece of rope that fits across the palm of

your hand.

A B