DNA Structure

The DNA code is held by the different letters of the nucleotides. As the cell "reads" the instructions on the DNA the different letters represent instructions. Every three letters makes up a word called a codon. A string of codons may look like this:

ATC TGA GGA AAT GAC CAG

Even though there are only four different letters, DNA molecules are thousands of letters long. This allows for billions and billions of different combinations.

Cells get their instructions on what do to from DNA. DNA acts sort of like a computer program. The cell is the computer or the hardware and the DNA is the program or code.

Within each string of DNA are sets of instructions called genes. A gene tells a cell how to make a specific protein. Proteins are used by the cell to perform certain functions, to grow, and to survive.

Although DNA looks like very thin long strings under a microscope, it turns out that DNA has a specific shape. This shape is called a double helix. On the outside of the double helix is the backbone which holds the DNA together. There are two sets of backbones that twist together. Between the backbones are the nucleotides represented by the letters A, T, C, and G. A different nucleotide connects to each backbone and then connects to another nucleotide in the center.

Only certain sets of nucleotides can fit together. You can think of them like puzzle pieces: A only connects with T and G only connects with C.

About 99.9 percent of the DNA of every person on the planet is exactly the same. It's that 0.1 percent that is different that makes us all unique. The double helix structure of DNA was discovered by Dr. James Watson and Francis Crick in 1953. If you unraveled all the DNA molecules in your body and placed them end to end, it would stretch to the Sun and back several times. DNA is organized into structures called chromosomes within the cell. DNA was first isolated and identified by Swiss biologist Friedrich Meischer in 1869.