Biology – DNA Model Kit
Name ________________________________________
Key:
Nitrogenous bases:
Pyrimidines:
4 Cytosine (C) – blue straw
5 Thymine (T) – green straw
Purines:
5 Adenine (A) – thicker orange straw
4 Guanine (G) – thicker yellow straw
20 Phosphates – white straw
9 Hydrogen bonds (white rod)
18 Deoxyribose sugars (black pentagon)
Not used:
gray straws and anything purple
DNA (deoxyribonucleic acid) makes up genes and is found in the chromosomes of all living things. With
an understanding of this master molecule of life, scientists know how genetic information is stored and
how it is transferred to new cells. They also understand how instructions encoded in DNA are sent to
direct the synthesis of proteins within a cell. In this model-building activity, you will examine the
structure of DNA and process of DNA replication.
Answer the following questions as you do this activity:
Part I – Structure of DNA
1. What is the monomer of DNA called? ___________________________________________________
What are the three parts? ____________________________________________________________
Begin by building eighteen nucleotides with your kit materials. Then construct a 9-rung ladder of DNA,
matching the correct complementary bases (A – T, C – G). The nine base pairs can be in any order.
2. Name the two parts of a nucleotide that alternate to make up the upright (or side) portion of the
DNA molecule. These two molecules form the “backbone” of DNA.
__________________________ and ___________________________
3. To which molecule of the backbone does each nitrogenous base attach? ______________________
4. What kind of bond joins the nitrogenous base to each other? ________________________________
5. What is the general overall structure of the DNA molecule? _________________________________
6. Lay or hold your model vertically. What are the nitrogenous bases on the left side of the molecule
you constructed? What are the complementary bases on the right side?
Left strand (list vertically)
Right strand (list vertically)
Part II – Replication of DNA
When DNA replicates, it is unzipped by an enzyme called helicase. This separates the two strands at
their hydrogen bonds. Each separated strand then serves as a template for the attachment of new
nucleotides by an enzyme called DNA polymerase. DNA polymerase also proofreads each new DNA
strand. This forms two new identical daughter DNA strands.
Separate your DNA molecule (at the hydrogen bonds) into two separate strands.
7. In your answer to the previous question (#6), fill in the complementary nitrogenous bases that
would be attached by DNA polymerase if your molecule were replicating. Be sure to write them on
the correct side of the template strands.
8. After DNA replication, are the two new DNA molecules identical to the parent? Why or why not?
9. After DNA replication, are the two new DNA molecules identical to each other? Why or why not?
10. Why and during what phase of the cell cycle does DNA replication take place?