DNA Basics

What is DNA made of?

-2 middle school students from Michigan

May 28, 2004

You may have heard of the "double helix" of DNA. Double helix refers to the shape of DNA, which is a ladder-like molecule that looks like the picture to the right. In DNA, two long strands (shown in yellow) wind around each other. These strands, the backbones of the ladder, are two long chains made of phosphate molecules.

The rungs of the ladder? Well, attached to each of these phosphates is the sugar that gives DNA its name, deoxyribose.

Now, connected to the sugars is one of the 4 'letters' of DNA, A, G, C, and T. These four letters are really shorthand for small molecules, bases, called adenine, thymine, cytosine and guanine.

Because of the way these molecules are structured, adenine bonds best with thymine, and cytosine bonds with guanine. So imagine you have a pair of these, an A-T pair, or a C-G pair. Now keep linking base pairs together by making a phosphate chain and you get what really looks like the ladder shown to the right.

Human DNA contains 3 billion of these base pairs! But because of the way the atoms are shaped in this ladder-like molecule, it actually twists around on itself, and looks like the double helix we talked about before.

Now since all the base pairs contain the same kind of phosphate and deoxyribose, the information of DNA has to be in the bases. The information is stored in DNA by using the 4 letters of the DNA code as a simple alphabet.

All words in this language are 3 bases long and every "word" of a gene codes for a different protein building block. The words get strung together to form "sentences" and these sentences are proteins.

So that's how DNA is structured. Two phosphate strands that twist around, each phosphate connected to a sugar, each sugar connected to a base, like rungs in a ladder. And DNA is read by reading, rung by rung, through the bases.

Okay, so I hope that answers your question. I guess the take-home message is that the information in the DNA strands is copied to messenger RNA (mRNA) and then the mRNA is translated by the cell into proteins. This information is passed down from one generation to the next, and is stored in the nucleus of each cell, in the form of long double-helix-shaped molecules made up of bases, sugar, and phosphate.

By Joylette Portlock, Stanford University