Name__________________________________________ Date ________ Period _______
Objective: Demonstrate the structure of DNA and the process of DNA replication.
1. Base-pair rule: Before you begin, refer to ch. 8 p.232-What does the “base-pair” rule of DNA
structure mean?
Materials:
Toothpicks=bonds between molecules
1__________ licorice = Phosphate group which is located on the _____________of DNA.
2-Red licorice = Deoxyribose sugar which is located ________________
3-Gummy bears = nitrogeneous bases
4 colors: ______________________= Adenine
______________________= Thymine
______________________= Guanine
______________________= Cytosine
Procedure:
1. Assign one nitrogen base to each of the four colors. Write the colors you have chosen in the
spaces above.
2. You have 8-12 gummy bears. Make sure that the “Chargoff” base-pair rule applies.
3. If you have 8 gummy bear “bases”, how many of each licorice color do you need? _______
4. Assemble a strand of DNA by connecting the different licorice color pieces together with
toothpicks. Remember that the phosphate group and deoxyribose to form the backbone.
5. Look at fig. 8.7 on page 233 of your book (or use your “DNA structure” notes)-What part of the
DNA backbone is attached to the bases-the sugar or phosphate?
6. (Chapter 8, page 230) Basic DNA structure-the nucleotide monomer: Write the following
words inside or around the correct shapes: deoxyribose sugar, phosphate, nitrogen containing
base. What type of nitrogenous base is shown below (purine or pyramidine)?
7. Add the gummy bases to the DNA backbone and
connect them to the correct backbone molecules.
8. It does not matter what order the bases go in as
long as the two correct bases are bonded together
in middle.
9. Assemble a complimentary strand to the one you just built. Again, add the bases to the correct
part of backbone.
10. Place this strand next to the first one so the bases touch according to the base pairing rules. Get
your teacher’s approval before moving on._______________
11. Practice simulating DNA replication with your candy:
a. Unzip the DNA double strand
b. What type of molecule is needed to break the bonds of the DNA molecule?
c. Assemble the proper new nucleotides one by one
d. What type of molecule is needed to bring the new nucleotides in and help bond them
together?
12. After you have practiced, demonstrate the process to your teacher. _______________
13. You may now eat your candy as you complete the conclusion questions.
Conclusion questions: Answer in complete sentences.
1. What is Chargaff’s rule and how does it apply to this lab activity (hint—it is the “base-pair rule”)?
2. Why does a cell need to duplicate its DNA? In what stage of the cell cycle does this happen?
3. Draw and label a picture of a nucleotide that is a purine structure (see page 230 and 231).
4. Who were the scientists that discovered DNA structure? What role did each of them play in the
discovery?
5. Based on your demonstration, why is DNA replication called “semi-conservative”?
6. Why did Watson and Crick propose that DNA is “self-duplicating”?
7. What alterations could make this activity more similar to actual DNA replication?