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BIO SCI 99 Study Guide - Midterm Guide: Oswald Avery, Photographic Film

Biological Sciences
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Lecture 2.
DNA Structure
1. How is directionality (or polarity) defined with respect to a strand of DNA or RNA?
2. Describe the major features of the DNA double helix structure, such as handedness, number
of bases per turn, major versus minor groove and being anti-parallel.
3. What are the two main types of chemical interactions that stablize the DNA duplex?
4. What does it mean to denature DNA? What two ways to denature DNA were discussed in
5. The opposite of denaturing, in this context, is annealing or hybridization. The term
‘hybridization’ implies having two strands of nucleic acid polymer from different sources.
6. Know how Tm is defined and how we can measure it by plotting 260 nm light absorbance at
different temperatures. How is Tm affected by pH, salt concentration and degree of
complementarity between the two strands of the DNA duplex.
7. Be familiar with the idea of a “probe”: a labelled segment (or oligonucleotide) of DNA or
RNA (usually single-stranded DNA) that is complementary to a sequence that you are
studying. This oligonucleotide can be labeled at the 5’ or 3’ end with a fluorescent chemical
group or the oligonucleotide can be made to include radioactive atoms, such as
phosphorous 32. The label gives you a way to detect and quantify probe amount using light
(for fluorescent labels) or some way to detect radioactivity (such as photographic film).
8. Be familiar with the Southern/Northern blotting technique. What can these techniques
detect? What is the basic workflow?
DNA as the Material of Heredity
1. Describe Frederick Griffith’s transforming principle.
2. What is transformation? How is it used in the lab? Do most cells in your transformation
reaction successfully uptake the exogenous DNA?
3. How did Oswald Avery modify the Griffith experiment and why?
4. What did the Hershey/Chase experiment demonstrate that the Oswald Avery experiment
did not? How was this demonstrated?
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