Double Helix DNA Model

Making a model is the best way of learning about the elements of a DNA molecule. You can use your model as a separate school project or as an addition to any DNA related science project.

A well made model enhances your display and results a higher level of attention to your presentation.

Introduction: 

       With over 100,000 different proteins to manufacture, how the heck does our body get it right?  When one thinks of the amount of information the body needs to keep track of, - eye, hair and skin color, protein sequence, toenail size, etc. - it would seem a task for a supercomputer to record all of the necessary information.  In essence it is.  But not a supercomputer made of silicon wafers and TV screens, rather one made of an intricate biomolecule called DNA.
        DNA (deoxyribonucleic acid) is in the family of molecules referred to as nucleic acids.  One strand of DNA has a backbone consisting of a polymer of the simple sugar deoxyribose bonded to something called a phosphate unit.  Very unimpressively then, the backbone of a strand of DNA resembles this:
  

sugar-phosphate-sugar-phosphate-sugar-phosphate-sugar-phosphate-...

In our model we use a white ball to represent sugar and a red ball to represent phosphate.

What is impressive about DNA is that each sugar molecule in the strand also binds to one of four different nucleotide bases.  These bases: Adenine (A), Guanine (G), Cytosine (C) and Thymine (T), are the beginnings of what we will soon see is a molecular alphabet.  Each sugar molecule in the DNA strand will bind to one nucleotide base.  Thus, as our description of DNA unfolds, we see that a single strand of the molecule looks more like this:

C T G A ...
sugar- phosphate- sugar- phosphate- sugar- phosphate- sugar- phosphate- ...

In our model we use light blue balls for Cytosine, light green balls for Guanine, yellow balls for Adenine and Orange balls for Thymine.

Each strand of DNA contains millions or even billions (in the case of human DNA) of nucleotide bases.  These bases are arranged in a specific order according to our genetic ancestry.  The order of these base units makes up the code for specific characteristics in the body, such as eye color or nose-hair length.  Just as we use 26 letters in various sequences to code for the words you are now reading, our body's DNA uses 4 letters (the 4 nucleotide bases) to code for millions of different characteristics.
        Each molecule of DNA is actually made up of 2 strands of DNA cross-linked together.  Each nucleotide base in the DNA strand will cross-link (via hydrogen bonds) with a nucleotide base in a second strand of DNA forming a structure that resembles a ladder.  These bases cross-link in a very specific order: A will only link with T (and vice-versa), and C will only link with G (and vice-versa).  Thus our picture of DNA now looks like this:

sugar- phosphate- sugar- phosphate- sugar- phosphate- sugar- phosphate- ...
G A C T ...
| | | | |
C T G A ...
sugar- phosphate- sugar- phosphate- sugar- phosphate- sugar- phosphate- ...


How to make the model?

Paint all the balls with water based or latex color. Following are the colors that we used in our model.

  • Yellow is for Adenine (A)
  • Green is for Guanine (G)
  • Blue is for Cytosine (C)
  • Orange is for Thymine (T)
  • White is for Sugar
  • Red is for Phosphate

Use toothpicks to make pairs of Adenine Thymine with sugars on the ends.

Also make pairs of Cytosine Guanine with sugars on the ends.

These pairs form the steps of the ladder in a DNA molecule.

The number of different color balls in our model is as follows:

Molecule Color of ball  Quantity
Sugar White 32
Phosphate Red 30
Adenine Yellow 8
Thymine orange 8
Cytosine Blue 8
Guanine Green 8
Connect the wood dowels together using wood glue to make a longer wood dowel. It may take a few hours for glue to dry.

Insert the long wood dowel into the base.

Place the first pair on the base and use a wire or string to tie it to the wood dowel.

Insert toothpicks in red balls (phosphates) so that the ball will be centered on the tooth pick. Insert one red ball over each white ball (sugar) and adjust the angles so your DNA model will become double helix. 
Mount the second pair over the previous one. Toothpicks from phosphates will enter the sugars of the new pair.

Continue with another set of phosphates and new pairs on top of each other. After a few rows, use another wire or string to tie the last pair to the column (wood dowel).

Continue that until your DNA model is ready.

If you want to separate your DNA model from the base, you will need to use a small amount of wood glue on the ends of toothpicks. If you do this, you can later remove the strings that you used to tie some of the pairs to the column and your DNA model will be removable. For more strength, you may use a very thin wire or string to connect the center of pairs together. If you do this, tie the string to the center of ladder every few steps and make sure that the string is well stretched.