Discovering DNA Structure

Tish Taylor
1994 Woodrow Wilson Biology Institute

Introduction

Instead of giving students copious notes and diagrams on the structure of DNA, why not let them discover the structure?

Teacher Information

Background Information: In this paper lab students will work in cooperative groups of four and manipulate paper nucleotides to discover the structure of DNA. When you have finished with this lab, you will have a great model of DNA that you can hang on the ceiling; it will reach to the floor and then some probably. This paper model can serve as a continual illustration as you discuss mitosis, amino acid sequences and protein synthesis. Students enjoy this lab and you save many frustrating moments trying to teach your students DNA structure.

Materials: copies of the student pages of "Discovering DNA Structure" (1/student); paper nucleotides (1/student) (enlarge the nucleotides so that each nucleotide fits on one sheet of paper); tape.

Teacher Preparations: Enlarge the nucleotides so that ONE nucleotide will fit on ONE sheet of paper. Each student will get one giant nucleotide to color and cut out. Color coding should be left on the sheet. Make sure that you prepare enough nucleotides so that 1/4th of each class represents each of the four DNA nucleotides. When assigning the cooperative learning groups of four, give one student an adenine nucleotide, one student a cytosine nucleotide, etc. When the groups come together the next day, each nucleotide will be represented.

Extension: Have your students learn the DNA SONG. When they learn and sing this little song, they know the structure of DNA. This would make a good follow-up to this lab. This song is to the tune of "Row, Row, Row Your Boat." Your students will have a lot of fun with this one. You might have them sing it in rounds, or have a contest between classes.

We love DNA
Made of nucleotides.
Sugar, phosphate and a base
Bonded down one side.

Adenine and thymine
Make a lovely pair.
Cytosine without guanine
Would feel very bare.

Oh-h-h, de-oxy-ri-i-bo
Nu-u-cleic acid
RNA is ri-i-bo
Nu-u-cleic acid

STUDENT PAGE
Discovering DNA Structure

D = deoxyribo
N = nucleic
A = acid

DNA contains the information for carrying out the activities of the cell. How this information is coded or passed from cell to cell was at one time unknown. To break the code, today you will do a paper lab to determine the structure of DNA and show how the genetic code is carried. Each member of your group has a molecule called a NUCLEOTIDE. DNA is made up of repeating units of nucleotides.

Look at your nucleotide and the nucleotides of the other members of your group. What are the THREE common parts of a nucleotide?

What is the ONE part of a nucleotide that differs among the four DIFFERENT nucleotides in your group?
List the four different kinds of nitrogen bases.
Manipulate the nucleotide pieces until you find the best fit. Join the nucleotide molecules in your group together like a puzzle. Use tape to connect and reinforce the molecules. You now have a molecule of DNA.
In the space below, explain WHERE the nucleotide molecules connect to each other.

A real DNA molecule consists of THOUSANDS of these pairs of nucleotides. What is the pairing arrangement of nitrogen bases?
_________ pairs with ________and _________ pairs with __________
Are there always going to be an EQUAL number of adenine and thymine nucleotides in a molecule?
Why?

Are there always going to be an EQUAL number of guanine and cytosine molecules in a molecule of DNA? Why?

Scientists abbreviate the nitrogen bases by using the first letter of each base. So,
A always binds to ____
G always binds to ____
In the space below, use the letters to show the sequence (order) of the bases in the DNA molecule that your group constructed. Begin at the top left side of your molecule.
____goes with ____
____goes with ____
The structure of DNA is actually in a DOUBLE HELIX arrangement.

DOUBLE HELIX means that the two long chains of nucleotides are arranged in a spiral like a twisted ladder.
The sides (or "uprights") of the ladder are made up of alternating _____________ and _____________ molecules. The steps (or "rungs") of the ladder are made of _______________ held together by HYDROGEN BONDS.
Bring your molecule to the front of the room and join it to the molecules of the other groups. We now have one large DNA molecule.