THE STRUCTURE OF DNA
OBJECTIVE
What discoveries led to a description of the DNA molecule?
INTRODUCTION
Avery, Hershey, and Chase had now shown the world that DNA was the crucial molecule for carrying the
genetic code. Two questions of overwhelming significance remained however:
1. How could a molecule such as DNA store the genetic code?
2. How could the molecule duplicate itself easily?
PROCEDURE
pages 344-349
Answer the following 12 questions on a separate sheet of paper. Upon answering these questions please note
that you answered them in the order in which these events occurred, therefore you now have a timeline that
summarizes the road toward understanding the structure of DNA.
Erwin Chargaff: 1950
1. Erwin Chargaff’s data provided what important piece of information about nucleotides?
Rosalind Franklin: 1952
1. What steps did she follow to conduct x-ray diffraction?
a.
b.
c.
d.
2. What did her x-ray photograph of DNA look like?
3. Franklin’s x-ray photograph revealed what three important clues about DNA
a.
b.
c.
4. Was her research alone successful in describing DNA structure? Explain.
James Watson and Francis Crick: Early 1950s
1. What technique were Watson and Crick using to determine the structure of DNA?
2. Was there research alone successful in describing the structure of DNA?
3. Did Franklin’s work help with understanding the structure of DNA?
Watson, Crick, and Chargaff: 1953
1. Franklin’s X-ray pattern helped account for what part of Watson and Crick’s DNA model?
2. Why did Watson and Crick call their model a double helix?
3. What did Watson and Crick realize from Chargaff’s information about base pairing?
4. How did Watson and Crick present their findings to the scientific community?