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Lab #8H - Constructing A Model of DNA Replication
BACKGROUND INFORMATION
DNA is a large molecule made out of two long, parallel strands of
nucleotides twisted around each other to form a double helix. Each nucleotide is
composed of a sugar, deoxyribose, bonded to a phosphate and nitrogen base.
There are four nitrogen bases, adenine, guanine, cytosine, and thymine. The
order of the bases in a DNA strand determines the order of amino acids in a
polypeptide chain. Polypeptide chains are used to make proteins. In this way
DNA directs the formation of proteins and controls the activity of the cell.
Proteins make up the structural components of the cell as well as enzymes
that control the cell’s chemical activities. In this laboratory investigation, you
will construct a model of DNA and use it to examine how DNA replicates or
duplicates, so that every new cell has a copy of DNA instructions.
PROBLEM
How does DNA replicate?
MATERIALS
2 DNA model kits
Blue = Adenine (4)
Green = Thymine (4)
Black = Deoxyribose (16)
White rod = hydrogen bond (8)
Tan = Cytosine (4)
Yellow= Guanine (4)
White = Phosphate (16)
fig. 1-1 Nucleotide
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PROCEDURE
1. Construct a model of a DNA nucleotide. Push together a phosphate
group, deoxyribose, and a Guanine. Then assemble the remaining seven
nucleotide models in this manner (in the nucleotide sequence from step 2).
2. Attach the eight nucleotides together in the following sequence: G, A, A,
T, C, G, G, T. This will form a single strand of your DNA Model.
3. Using your base pairing rules, construct a second strand of DNA that is
complimentary to the first. Now you will have one complete molecule of
DNA that looks something like fig.1-2.
fig. 1-2 DNA Model
4. Separate the two strands and use each as a template to construct a new
complementary strand. Now you have two complete molecules of DNA.
OBSERVATION
1. What is the sequence of the nitrogen bases in the complementary strand of
your original strand of DNA?
2. How many models did you construct? Were the base sequences of each
model the same?
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ANALYSIS AND CONCLUSION
1. Why do you think complementary base pairing is necessary for
replication?
2. Compare the base sequence of the original model with the replicated
model.
CRITICAL THINKING
1. If the DNA code for an amino acid is a triplet of bases, what is the
smallest change in the arrangement of bases that would result in a
change in the polypeptide produced? Explain.
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