Color this page with the colors used in your Lego model! 
LEGO DNA
Name: ___________________________
Date:________ Period:____ Group:____
Deoxyribonucleic acid (DNA) is a complex molecule found in all living organisms. DNA is the
chemical of which genes are composed. DNA coils into tightly-wound units: our chromosomes. An
understanding of the organization of this molecule has answered many questions in the exploration of
genetics; scientists now know how chromosomes can duplicate during cell division and transfer their
genetic information to new chromosomes, and understand how chromosomes in the cell nucleus can
direct the formation of specific proteins outside the nucleus.
Part A: Structure of DNA Nucleotides
Two important molecules which make up DNA are deoxyribose and phosphoric acid. Deoxyribose
is a sugar, or rather, a carbohydrate. The chemical structures for each are shown:
Deoxyribose
Phosphoric Acid
In addition, there are four different molecules called bases. For DNA, these include: Guanine,
Cytosine, Thymine and Adenine. Their chemical structures are shown:
A molecule of deoxyribose joins with
phosphoric acid and any one of the four bases to
form a chemical compound called a nucleotide.
A nucleotide is named for the base that joins
with the deoxyribose. For example, if thymine
attaches to a deoxyribose, the molecule is called
a thymine nucleotide, or simply thymine for
short. Because of their chemical composition
and available hydrogens, adenine and thymine
complement each other with double hydrogen
bonds. Likewise, cytosine and guanine are
complementary to each other with triple
hydrogen bonds.
Answer the following questions based on the introduction:
1. Give the molecular formula for:
a. Deoxyribose: C__H__O__
b. Phosphoric Acid: H__P__O__
1. What is a base?
2. What is a nucleotide?
3. List the four different nucleotides:
4. Which bases pair together? WHY?
5. What do the four nucleotides have in common?
6. What is different about the four nucleotides?
Part B: DNA Lego Building
Working in pairs you will construct a 10-rung DNA model using the following procedure:
1. Build one type of each nucleotide using the instructional sheets provided.
Thymine (red), Adenine (green), Cytosine (blue), and Guanine (yellow).
Draw each below in color, including the attached deoxyribose/phosphoric acid:
Thymine
Adenine
Cytosine
Guanine
2. Construct four more of EACH type of nucleotide. You should have a total of FIVE of each.
3. Match and join DNA nucleotides using their hydrogen bonds (two for A-T, three for G-C) to
make complementary pairs of nucleotides. You should now have five full complementary pairs
of nucleotides.
4. Stack your deoxyribose/phosphoric acid (red blocks) in a twisted pattern to resemble a spiral
staircase with the nucleotides as the middle steps. This is the double-helix molecule of DNA.
Your completed model should look like a ladder with matched bases as the rungs. Deoxyribose and
phosphoric acid molecules join to form the sides or uprights of the ladder, as represented by the red
and black blocks around the outside. Base molecules join by hydrogen bonding to form the rungs of
the ladder, as represented by the red, green, blue and yellow “steps”. Besides being shaped like a
ladder, a DNA molecule is also twisted and resembles a spiral staircase, or a double-helix.
5. Get a stamp from your teacher. While you wait, go back to page one and color in all of the sugar,
phosphate, and base molecules with the colors that you are using in your Lego model.
Answer the following questions based on your model and your understanding of DNA:
1. If DNA is “ladder-like,” which two molecules of a nucleotide make up the sides or upright
portion of the ladder?
2. List out the series of nucleotides on the LEFT side of your helix (use letters A, T, G, C):
3. List out the complementary strand on the RIGHT side of your helix (use letters A, T, G, C):
4. What is meant by the term complementary strand?
5. If five cytosine bases appear in a DNA model, how many guanine bases should there be? ______
6. Your model should have five cytosine bases; does the number of guanine bases in your model
agree with your prediction?
7. If the following are bases on the LEFT side of a DNA molecule, list the bases that would make up
the complementary strand on the RIGHT side of the DNA molecule:
a. Thymine:_________________
b. Cytosine:_________________
c. Guanine:__________________
d. Adenine:__________________
Part C: RNA Structure
Your DNA model represents only a short length of the DNA that is tightly wound and coiled into a
chromosome. An entire chromosome has thousands of rungs rather than only 10. Although your
model is only a small part of a chromosome, its complementary pairing represents how DNA
replicates throughout an entire chromosome during mitosis and meiosis.
Besides ensuring the exact replication of chromosomes, the sequence (order) and parings of bases are
a genetic code of the instructions for the entire cell. How does a cell “read” the chemical message
coded in its DNA in the form of specific base sequences? Part of the answer lies within a second
molecule in the nucleus of cells called ribonucleic acid (RNA).
Part C: RNA Structure Continued
RNA is similar to DNA in that its molecules are also formed from nucleotides. However, deoxyribose
and thymine are not found in RNA. Two other molecules, ribose and uracil, are present instead.
Ribose replaces deoxyribose and uracil replaces thymine. Also, RNA is single-stranded and does not
form a ladder on its own, but rather one half side of a ladder (the left or right only). The smaller size
allows RNA to cross the nuclear membrane whereas the double-stranded DNA molecule is confined
within the nucleus.
Answer the following questions based on the reading:
1. Which DNA base does uracil replace in RNA?
2. What chemical replaces deoxyribose in RNA?
3. In RNA, what pairs with the following bases?
a. Guanine: ________________
b. Adenine: ________________
c. Cytosine: ________________
d. Uracil: __________________
4. Complete the table below by using check marks to indicate which molecule each characteristic
applies. Some may apply to both molecules:
DNA
Deoxyribonucleic acid
Ribonucleic acid
Phosphoric acid
Ribose present
Deoxyribose present
Adenine present
Thymine present
Guanine present
Cytosine present
Uracil present
Made up of nucleotide bases
Double-stranded helix
Single-stranded
Can leave cell membranes
Remains only within nucleus
Contains a chemical message or code
RNA