SUPPLEMENTARY MATERIAL Yale University: Science Education Outreach Program

III.A) 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.