Chapter 16 Free Response Questions

1. Experiments by the following scientists provided critical information concerning DNA. Describe each classic experiment and indicate how it provided evidence for the chemical nature of the gene.

a. Griffith: discovery of bacterial transformation

b. Avery: discovery that bacterial transformation is due to DNA

In your answer list each group of researchers and their respective experiments separately.

Griffith: Use my lecture notes or fig 16.1 as your guide. Be sure to clearly distinguish the 5 steps in the experiment and what they each showed. Use Illustrations and be sure to describe each step clearly in words as well. Make sure you give the name of the strain of bacteria that was used, the difference between rough and smooth strains, and the importance of killing and then mixing the different strains. Clearly state what the result of these experiments proved to the world for the very first time. It was revolutionary!

Avery: His work was a follow-up to Griffith’s work. Some books look at Griffith and Avery as one big experiment but their research was separate; Avery extended the ideas first discovered by Griffith. Be sure you explain this. What was the major thing that he discovered which was new and different from Griffith?

2. Experiments by the following scientists provided critical information concerning DNA. Describe this classic experiment and indicate how it provided evidence for the chemical nature of the gene- Hershey and Chase: discovery that DNA is the hereditary material in viruses

•Use my lecture notes or figure 16.2 as your guide.

•Be sure to distinguish between a bacteria and a bacteriophage (they are NOT the same thing!). Be sure to explain why the use of a bacteriophage was SO clever for doing their experiments.

•Explain the different steps of their experiments. Use illustrations and be sure to state each step in words as well.

•Be sure to explain the purpose of radioactive labeling (how and why was it used), explain the significance of sulfur and phosphorus (key molecules), explain why the organisms were put in a blender.

•Clearly state what the result of these experiments proved, beyond a reasonable doubt. It was very important!

3. Experiments by the following scientist provided critical information concerning DNA. Describe the classic experiment and indicate how it provided evidence for the chemical nature of the gene. See page 281 in the book, first column.

a. Chargaff: Ratio of nitrogenous bases in DNA

Chargaff: His results were very important for Watson and Crick. Describe what he discovered. It was so important that it has subsequently been called “Chargaff’s Rules”

4. Experiments by the following scientists provided critical information concerning DNA. Describe their classic experiment and indicate how it provided evidence for the chemical nature of the gene.

a. Meselson and Stahl: Demonstration of how DNA replication occurs in bacteria

Meselson and Stahl: After Watson and Crick determined that DNA was the molecule of heredity it was not clearly understood how DNA replicated. Using figures 16.8 and 16.9 from your book describe the three different possible models of DNA replication. Use illustrations in your explanation- use two different colors to indicate the different strands of DNA to clearly illustrate what is going on. Explain the ground-breaking experiment that resolved this debate (known as "the most beautiful experiment in biology"). Be sure to clearly explain the reason two different isotopes of nitrogen were used and the significance of “density gradient centrifugation." This animation might be very helpful in writing this up.

5. Describe the structure of DNA using the guidelines below. Be sure to describe each item in words, even if asked to include an illustration. You may use my lecture notes, the book, or the CD ROM. Activity 16.1 on the CD ROM is excellent and will be of great help in answering this question. Be sure to include the following things:

a. What is the basic structure of a nucleotide? Include an illustration. (fig 16.3 & chapter 5, fig 5.27)

b. What are the differences between purines and pyrimidines? Identify which nitrogenous bases are purines and which are pyrimidines. Include an illustration of each. (fig 16.3 & chapter 5, fig 5.27)

c. Illustrate one strand of DNA pointing out the sugar-phosphate backbone. Discuss what is meant by a 3’-5’ linkage. (figures 16.3, 16.5, 16.12 will be helpful)

d. Illustrate the second complementary strand of DNA. Show how the bases pair. Describe the kind of bond involved in the base pairing. Illustrate the anti-parallel nature of the double strands. (figures 16.5, 16.6, & 16.12 will be helpful)

e. Describe how DNA differs from RNA. (the CD ROM activity 16.1 is great for this).

6. Explain and illustrate DNA replication. Figure 16.16 is a nice overview. The CD ROM is excellent. Be sure to show each of the steps in order. Explain all the major molecules that contribute to the process. Here is a list of major things that occur. The list is NOT exhaustive but will give you an idea of what I am expecting you to know.

a. Explain the importance of helicases.

b. What is the function of single-stranded binding proteins?

c. What is the function of DNA Polymerase?

d. What direction is the new DNA strand synthesized? What is meant by 5’ and 3’?

e. What is the difference between the leading strand and the lagging strand?

f. What is primase and what is it used for?

g. What in the world is an Okazaki fragment?

h. What is the function of DNA ligase?