Name: ____________________________
Period: _____
Date: ____________
LEGO DNA
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.
Name: ____________________________
Period: _____
Date: ____________
Answer the following questions based on the previous reading:
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, 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.
Name: ____________________________
Period: _____
Date: ____________
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.
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).
Name: ____________________________
Period: _____
Date: ____________
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 singlestranded 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 doublestranded 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