History of DNA & Replication – Exploration Assignment
Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the
polymerase chain reaction (PCR).
1. Polymerase chain reaction (PCR) is a key technique in DNA manipulation and
analysis.
a. State the main uses of PCR.
b. State the name of the specialized apparatus needed to support this
process.
c. Define the three key stages in the process of PCR:
i. Denaturation
ii. Annealing
iii. Elongation
d. If one cycle of PCR yields two identical copies of the DNA sequence.
Calculate how many copies 20 cycles would yield.
Analysis of Meselson and Stahl’s results to obtain support for the theory of
semi-conservative replication of DNA.
2. The image below details the three possible methods of DNA replication.
Review your understanding of Meselson and Stahl’s experiments by reading
page 73 in the textbook and using the McGraw and Hill animation found at:
http://highered.mheducation.com/olc/dl/120076/bio22.swf
a. Which (if any) mechanisms of DNA replication are falsified by this
result?
b. Explain why the identified mechanism(s) are falsified.
Analysis of results of the Hershey and Chase experiment providing evidence
that DNA is the genetic material.
3. Use the McGraw and Hill animation to learn about the Hershey-Chase
experiment providing evidence that DNA is the genetic material. The
animation can be found at:
http://highered.mheducation.com/sites/9834092339/student_view0/chapt
er14/hershey_and_chase_experiment.html
a. Explain why sulfur was used in one experiment and phosphorus in the
other.
b. Describe what the supernatant is in the experiment.
c. Explain why most the radioactive sulfur was found in the supernatant.
d. Explain why little of the radioactive phosphorous was found in the
supernatant, i.e. most in the pellet.