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The Gene Hunters
 
Teaching Guide
In a "Passion for DNA", you met James Watson, co-founder of the double helix structure of DNA. Short for deoxyribonucleic acid, DNA is a special molecule that carries the code for every protein manufactured in your body. With a molecular eye-view, you'd discover that the DNA molecule is formed by subunits called nucleotides. There are four different nucleotides, each containing a sugar, phosphate and nitrogen containing base. The names of these four nitrogen-containing bases are cytosine, thymine, adenine, and guanine. Two side-by-side strands of these four bases join together to form a staircase-like structure called a double helix.
 

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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

  1. 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)

  2. Cut out small segments of straws, each about 1 centimeter in length.
  3. Use tape to attach a straw segment to the back of one of the cutouts as shown below.
  4. 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


  5. Repeat this procedure until you finished attaching cotton swabs and straw segments to all 16 cutouts.

Part 2- Build a Double Helix

  1. From these nucleotides attached with cotton swabs, choose four, one representing each base (ATGC).
  2. 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.

  3. 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.
  4. Once the two strands have been assembled, use tape to connect them together.
  5. 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.
  6. 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

  1. What is a nucleotide?
  2. What are the three building blocks of a nucleotide?
  3. How many different nitrogen bases are found in DNA?
  4. 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.


Answers

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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