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OBJECTIVE
This
activity page will offer:
-
An understanding of the building blocks of DNA
- Construction
experience in assembling a DNA model
- A
visualization of the DNA double helix
MATERIALS
- Color copies of nucleotide templates provided below
- Cotton swabs
- Straws
- Centimeter ruler
- Scissors
- Tape
PROCEDURE
Part
1- The Basic Building Block
- Use scissors to cut apart at least four groups of the
four nitrogen containing bases of DNA shown in the diagram:
Guanine, Cytosine, Adenine,Thymine. (16 pieces of paper
in total)
- Cut out small segments of straws, each about 1 centimeter
in length.
- Use tape to attach a straw segment to the back of one
of the cutouts as shown below.
- Remove and discard one of the tuffs from a cotton swab.
Use tape to attached the shaft of this swab to the nucleotide
on the side opposite the straw segment - SEE DIAGRAM
- Repeat this procedure until you finished attaching cotton
swabs and straw segments to all 16 cutouts.
Part
2- Build a Double Helix
- From these nucleotides attached with cotton swabs, choose
four, one representing each base (ATGC).
- Insert the cotton shaft of one into the straw segment
of an adjoining nucleotide. Continue connecting the pieces
until you have assembled a chain of four bases - SEE DIAGRAM.
- Construct a complimentary strand of DNA. This complementary
strand must have a base sequence that "pairs" with the already
completed strand. For example, adenine must be paired with
thymine.
- Once the two strands have been assembled, use tape to
connect them together.
- Repeat this procedure for your 8 remaining bases, attaching
them first to each other and then to their matched pair
as shown in the diagram.
- Next, attach the top most cotton balls to the underside
of a desk. The rest of the model will hang freely. While
supporting the model, put a slight twist in its shape. This
twist creates the characteristic "double helix" of the DNA
molecule.
ANALYSIS
Analyze Your Model
- What is a nucleotide?
- What are the three building blocks of a nucleotide?
- How many different nitrogen bases are found in DNA?
- How do the bases pair up?
Critical
Analysis
Does one strand of DNA offer
enough clues for assembling its complementary strand? If so,
how? And why is this important?
Complementary
Order
What
is the base order for the complementary DNA strand to the
sequence ATTGCAAGGCC?
WEB
CONNECTION
DNA
- From the Beginning
Check out this animated primer on DNA basics.
Primer
on Molecular Genetics
From the Department of Energy
A
Structure for Deoxyribose Nucleic Acid
For
more Web links on this topic - visit our Resources
Section.
The
activities in this guide were contributed by Michael DiSpezio,
a Massachusetts-based science writer and author of "Critical
Thinking Puzzles" and "Awesome Experiments in Light & Sound"
(Sterling Publishing Co., NY).
Academic Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools,
Wayland, MA
Suzanne Panico, Science Department, Fenway High School, Boston,
MA
Anne E. Jones, Science Department, Wayland Middle School,
Wayland, MA
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