Name: __________________________________________________________________ Period 1 2 3 5 6 7
Modeling DNA and DNA Replication
Background Information
Inside the nucleus of every cell are long strands of DNA, the genetic code that holds all the information to make and
control every cell within a living organism. DNA, which stand for deoxyribonucleic acid, resembles a long twisted ladder.
A sugar-phosphate molecule makes up the sides of the ladder. The rungs of the ladder are made of four bases: thymine
(T), adenine (A), cytosine (C), and guanine (G). It takes two bases to form a rung of the ladder. A sugar molecule, a
phosphate molecule, and a base together make something called a nucleotide. Nucleotides, when linked together, form
one side of the ladder. The other side of the ladder is made up of nucleotides that have the matching base pairs.
Thymine always pairs with adenine, and cytosine always pairs with guanine.
During DNA replication, the DNA “ladder” unzips along the matching base pairs into two strands. New nucleotides move
into each side of the unzipped ladder. The nucleotides match up with the correct matching base pair (A with T and C
with G). When the matching up is completed you are left with two identical strands of DNA. The cell is now ready to
divide and each new cell will get a copy of the DNA.
Objective:
To learn about the basic structure of DNA and to model how DNA replicates itself before cell division.
Materials:
Molecules that make up DNA sheet, Colored pencils, Scissors, Glue, 1 piece of construction paper
PART 1: Building the DNA Molecule
1. Color code the nitrogen bases, phosphate, and (deoxyribose) Sugar molecules as follows: Adenine = red, Guanine =
green, Thymine = yellow, Cytosine = blue, Phosphate = brown, Deoxyribose = purple
2. Cut out all of the units as neatly as possible. Keep track of them!
3. Using the small squares and stars as guides, line up the bases, phosphates, and sugars. Glue the appropriate parts
together to form individual nucleotides (nitrogen base+ phosphate + Sugar).
4. Construct the left side of your DNA molecule using the following sequence: C (top), T, G, A (bottom). Glue the
nucleotides together and label it “L1” on the back.
5. Construct the right side of your DNA model by adding complimentary bases. Remember the base pairing rules! Once
you have the correct order of base pair for the right side glue the right strand together and label it R1. DO NOT GLUE
THE TWO STRANDS TOGETHER YET!
6. Show your DNA model to the teacher then answer the following questions.
Analysis Questions Part 1
1. Describe the shape of the DNA molecule. Draw a picture.
Name: __________________________________________________________________ Period 1 2 3 5 6 7
2. What are the three components of a nucleotide?
3. Suppose you know the sequence of bases on one strand of DNA (one side of the ladder) is AGCTCAG. What would the
sequence of bases be on the opposite strand?
4. Assume that a 100 base-pair double helix contains 45 cytosine’s. How many adenine’s would there be?
Part 2: Modeling DNA replication
1. Separate the left side of your DNA molecule from the right side, leaving a space of about 6-8 inches. This will
represent the “unzipping” of the nitrogen bases.
2. Use the remaining nucleotides to complete one molecule using the left side as the model. Once all the nucleotides are
in the right place, glue the entire molecule together.
3. Build a second DNA model by adding new nucleotides to the right half of the original piece of the molecule. Glue this
together as well.
4. Show the teacher your completed strands and then answer the following question.
Analysis Question Part 2
1. Explain the process of DNA replication. Use the words: nucleotide, parent strand, new strand, and nitrogen bases.