Biology
Unit 5 DNA and RNA
Chapter 12.
DNA Repeat
Name ________________________________
Chance is the only true source of novelty
-Francis Crick
Purpose. The purpose of this investigation is to use models to determine how DNA is replicated.
Outcome. Each group will construct two strands of DNA that have a complementary sequence to
the original two strands.
Problem to investigate – How is DNA replicated? Summarize the class discussion below.
Materials. Each group needs to obtain the following pieces.
-Sugars: 36 brown pieces
-phosphates: 36 orange pieces -Adenines (A) – 12 green pieces
-Thymines (T): 12 yellow pieces -Guanines: 6 red pieces
-Cytosines (C): - 6 blue pieces
Procedure.
1. To model a nucleotide, tape together a phosphate group, a sugar and a guanine molecule.
G
S
P
2. Assemble 8 additional nucleotide models with the following bases: 3 thymines (T), 3 adenines
(A), 2 cytosines (C).
Get my signature here when completed __________________
3. To model a single strand of DNA, tape the sugar of each nucleotide to the phosphate group of the
next nucleotide in the following order: G T T A C A A T C
G
T
T
Get my signature when completed ________________
4. Construct a strand of DNA that is complementary to the first. (Remember C bonds with G and A
bonds with T). Tape the nucleotides together as you did in step 3 and show me that strand!
Get my signature here! _____________________
5. Place the two strands together so that their complementary nucleotides face each other. Write
original on each strand using a marker. This simulates a DNA molecule in a living cell.
C
A
A
G
T
T
6. Separate the two strands. Simulate the action of DNA polymerase by constructing a new
complementary strand for each original strand.
7. Tape the bases of each new strand to the complementary bases of its original matching strand.
You should now have two new DNA Molecules. In each one molecule one of the strands is from the
original.
Get my signature for your strands! _____________________
Analysis.
1. How does the new double-stranded DNA models compare with your original DNA model?
2. After a cell’s DNA is replicated, the cell may divide in two. Each new cell receives one copy
of the original cell’s DNA. According to your model, how are the new strands and the
original strands divided between the two new cells?
3. What are the three amino acids that would be coded for in your DNA molecule? (see page
303).
GTT is ________________________________________
ACA is ________________________________________
ATC is ________________________________________
4. What problems would you expect to occur if DNA was not copied accurately as it is
replicated? (Consider your answer to #3 above!)
5. What are three mistakes that could occur in the DNA replication of this molecule?
6. The model you made is intended to help visualize the DNA replication process. How is this
model not an accurate picture of what DNA is really like?
7. DNA only codes for the production of proteins. What must be true of proteins if they are to
help cells survive?