DNA or deoxyribonucleic acid is the foundation of all life. The double helix structure
allows for an infinite combination of the four nucleotides that determine characteristics
of organisms. The order in which these nucleotides are stacked and combined creates the
diversity in all living organisms. No two sets of DNA are exactly alike.
The four nucleotides are:
adenine (A)
cytosine (C)
guanine (G)
thymine (T)
*(In RNA, uracil (U), takes the place of thymine.)
These are held together by hydrogen bonds.
They pair up, and adenine and thymine pair together, while cytosine and guanine
pair together. These pairs are known as "base pairs."
DNA was first identified in the late 1860s by Swiss chemist Friedrich Miescher. The
double helix structure was discovered in the 1950s by two scientists, James Watson and
Francis Crick, who won the Nobel Prize in 1962, along with Maurice Wilkins, for the
discovery.
Today you will build your own basic model of DNA structure with pipe cleaners and
beads.
You will have a strand of DNA that has 8 pairs of nucleotides (base pairs).
First you must learn to pair the nucleotides correctly. Remember, adenine (A) pairs with
thymine (T), and cystosine (C) pairs with guanine (G).
Here is one side of the DNA. Pair each nucleotide correctly.
Example:
Adenine (A) - ____________________
-->
Adenine (A) - Thymine (T)
Your strand:
Now write in the colors you'll
need for the beads to
represent your pairings:
Adenine (A) - _____________________
__________ - __________
Guanine (G) - _____________________
__________ - __________
Cytosine (C) - _____________________
__________ - __________
Adenine (A) - _____________________
__________ - __________
Thymine (T) - _____________________
__________ - __________
Cytosine (C) - _____________________
__________ - __________
Thymine (T) - _____________________
__________ - __________
Guanine (G) - _____________________
__________ - __________
Materials:
2 full-sized pipe cleaners
8 small pieces of pipe cleaner (about 3-4" in length)
beads in 4 different colors to represent the different DNA nucleotides
1) Determine which nucleotides are paired with each other to determine the sequence for
your DNA model, creating your base pairs.
2) Figure out which colors of beads are needed to represent each base pair of the DNA
helix.
3) Use 2 beads of the same color for each nucleotide of the base pair. Attach them
together by putting them on the center of the small pipe cleaner pieces that represent the
hydrogen bonds holding the nucleotides together. (There will be four beads on each small
piece of pipe cleaner.) The extra pipe cleaner on the end will be used to connect the base
pairs to the backbones of the DNA helix (the large pipe cleaners.)
4) Attach each "rung" of the DNA helix to the large pipe cleaners by spacing them a good
distance apart. (approximately 1/2" to 1" apart)
5) Once all the base pairs are connected to the DNA backbones, gently twist the DNA
structure to give it it's three-dimensional shape.