At the end of the assignment, you will have answered each of the questions found in the DNA Scientist
Chart. In order to do this, you will be reading pages from your textbook (Ch. 16) in addition to the information provided on the smaller half sheets. I recommend either printing the chart so that you can fill it in or copying the main point of the question so that you can use the answers to help you study.

Scientist & Questions
Frederick Griffith
1.
Draw and label a diagram showing the four experiments of Frederick
Griffith.
2.
Describe the importance of the results from experiment #4.
3.
What is “transformation” (based on the information in this experiment)?
Oswald Avery
1.
Define “heritable.”
2.
Describe the set up of Avery’s experiment.
3.
What was the goal of Avery’s experiment?
4.
What was the result of Avery’s experiment?
Answers to Questions

Alfred Hershey & Martha Chase
1.
Describe the basic make-up of a virus and how it works.
2.
Describe what “T2” was and what was known about it.
3.
What was the question that
Hershey and Chase were trying to answer?
4.
Why did Hershey & Chase radioactively label the sulfur in 1 treatment and the phosphorus in a
2 nd treatment?
5.
What did Hershey and Chase discover in their experiment?
6.
Based on the results of their experiment, what did Hershey and
Chase conclude?
7.
Does this provide evidence that
DNA or protein is the genetic material?
Wilkins & Franklin
1.
Describe the technique of x-ray crystallography.

2.
Based on her x-ray diffraction of
DNA, list two things that Rosalind
Franklin discovered about the structure of DNA.
3.
What question did Rosalind still have about DNA?
Watson & Crick
1.
Prior to Chargaff’s work, list what was already known about DNA.
2.
Based on his experiments, what did
Chargaff conclude about the base composition of DNA?
3.
What are “Chargaff’s rules”?
4.
List the five scientists who were competing to figure out the structure of DNA.
5.
Watson and Crick based their model of DNA on what?
6.
List the four pieces of information that Watson and Crick were able to figure out from Rosalind’s photograph.
7.
Describe the structure of DNA that Watson and Crick proposed.
8.
Contrast pyrimidines and purines.
9.
Why must a purine pair with a pyrimidine?
10.
Based on Watson and Crick’s model, what are the base pairing rules?
11.
How does their model explain
Chargaff’s rules?

In 1928 an army medical officer named Frederick Griffith was trying to find a vaccine against streptococcus pneumoniae
(the bacteria that causes pneumonia, a lung disease), but instead made a breakthrough in the world of heredity. He did four experiments in which he injected strands of bacteria into mice, one strand that was harmless (R) and one that was harmful (S). o In his first experiment, he injected the live R bacteria cells into a group of mice and the mice lived. o In his second experiment, he injected the live S bacteria cells into a group of mice and mice died. o In his third experiment, he killed the harmful S cells with extreme heat, and then injected the dead S cells into a group of mice and the mice lived. o In his last experiment, he added live R cell (which are harmless) to the already dead heat-killed S cells, and then injected it into a group of mice, but the mice died!
Griffith found from this experiment that even though he had killed the S cells, he hadn’t destroyed their hereditary material, which was the one part that caused the disease! When more experiments had been done, it was discovered that the harmless R cells had used the information from the hereditary material of the dead S cells and became harmful; he called this hereditary transformation.
(Oh and by the way… he never did find the vaccine.)
In 1932, Avery turned his attention to an experiment carried out by a British microbiologist named Frederick Griffith.
Griffith worked with two strains of streptococcus pneumoniae (the bacteria that causes pneumonia, a lung disease) –one encircled by a carbohydrate capsule that was deadly, and another that lacked a capsule and was not deadly (harmless).
Griffith’s results showed that the deadly strain could somehow convert, or transform, the harmless strain into the deadly strain. Furthermore, the transformation was heritable—i.e. able to be passed on to succeeding generations of bacteria. Avery, along with many other scientists, set out to determine the chemical nature of the substance that allowed the transformation to occur. In 1944, he and his colleagues reported that the transforming substance—the genetic material of the cell—was DNA. This result was met initially with skepticism, as many scientists believed that proteins would prove to be the genetic information. Eventually, however, the role of DNA was proved, and Avery’s contribution to genetics was recognized.
Read pages 297-298 in your textbook and then answer the following questions.

Read pages 294-296 in your textbook and then answer the following questions.
The technique with which Maurice Wilkins and Rosalind Franklin set out to discover the structure of DNA is called X-ray crystallography. With this technique a crystal is exposed to x-rays in order to produce a diffraction pattern. If the crystal is pure enough and the diffraction pattern is acquired very carefully, it is possible to reconstruct the positions of the atoms in the molecules that make up the basic unit of the crystal called the unit cell. By the early 1950s, scientists were just learning how to do this for biological molecules as complex as DNA.
Rosalind Franklin provided the first DNA crystals pure enough to yield interpretable diffraction patterns.
She then went on to obtain excellent X-ray diffraction patterns of DNA, and using a combination of crystallographic theory and chemical reasoning, discovered important basic facts about its structure. She discovered that the sugar-phosphate backbone of DNA lies on the outside of the molecule, not the inside as was previously thought. She discovered the helical structure of DNA has two strands, not three as proposed in competing hypotheses. She gave quantitative details about the shape and size of the double helix. The all- important missing piece of the puzzle, that she could not discover from her data, was how the bases paired on the inside of the helix, and thus the secret of heredity itself.
After Franklin's work was presented at a routine seminar, aspects of her results were informally communicated to Watson and Crick by Maurice Wilkins without Rosalind’s knowledge. It was Watson and
Crick who put all the pieces of the puzzle together from a variety of sources, including Franklin's results, to build their ultimately correct and complete description of DNA's 3-dimensional structure.
Rosalind Franklin never knew that Watson and Crick had gotten access to her results. After Watson and
Crick published their results, Franklin did not seem bitter about their accomplishment. After her death,
Watson and Crick made it abundantly clear in public lectures that they could not have discovered the structure of DNA without her work. However, because the Nobel Prize is not awarded posthumously,
Rosalind Franklin could not be cited for her essential role in the discovery of the physical basis of genetic heredity.
To think about: How do you feel about Maurice Wilkins action…do you think he was deceptive? Or was it a necessary move on his part to help the field of science?