SUPPLEMENTARY MATERIAL
Lesson III
The Structure of DNA
A DNA molecule consists of two strands twisted together in a double
helix.
Each strand is a string of bases, like beads on a string.
There are four kinds of bases, which are called Guanine, Cystosine,
Adenine, and Thymine.
The order, or sequence, of the four bases G, C, A, and T determines the
function of the gene.
The bases of the two strands line up opposite each other - this is called
base pairing.
Base pairing has two rules: G always pairs with C, and A always pairs
with T.
A mutation (change in the sequence) can change the way a gene works.
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