What is DNA?

Susanna Pilny for redOrbit.com – Your Universe Online
It’s mentioned practically everywhere—the news, detective shows, that obnoxious friend who uses words like “insouciant” or “sesquipedalian” into small talk—but it’s now taken for granted that people know what DNA is. Sure, we all know DNA is the code of life…but what does that even mean?
Of course, what we know (and what we think we know) about DNA has filled many books, but we’ll give you a brief run-down so the next time you run into that precocious friend, you can throw a few amino acids their way.
Let’s start by building a strand a DNA

First, you need nucleotides. There are four different kinds in human (though, some now say six), but all of them contain sugar (deoxyribose), phosphate, and a base. The bases are the only parts that are different between the nucleotides, and there are (surprise) four kinds: adenine (A), guanine (G), thymine (T), and cytosine (C). Each kind can be modified for more variation, but the base structure remains intact.
These four nucleotides are then attached together to form a line of DNA, and the order they’re in is what makes you, well…you. Think of it this way: The alphabet has 26 letters, and by arranging them in different ways, you get different words with different meanings. In DNA, the four nucleotides are arranged in different ways to get you different genes.
In DNA, a second line of nucleotides is paired with the first, and together these two strands twist into a spiral—the double helix. However, the DNA found in each cell would be about 6 feet long, so it has to be packaged into something smaller—which is where histones come in. Histones are small, ball-like proteins that the DNA wraps around, and from there the DNA forms a tight coil, loops, and then condenses into a tiny molecule called a chromosome. To say it differently: a chromosome is DNA, just in a tighter form than a straight-up helix.

But how do we go from genes to human beings?
Not easily.
So remember how the order of the four nucleotides determines each gene? Well, mRNA (a cousin of DNA) actually “photocopies” the order of a gene and brings itself to a piece of cellular machinery called a ribosome to be “read”.
The ribosome “reads” the nucleotides in groups of three. For ribosomes, every three-piece combination of nucleotides specifies one of the 20 basic parts of a protein. Or, our four “letters” (A, G, T, and C) are rearranged into three-letter “words” (of which there are 20). These twenty “words” are called amino acids, and together they form proteins. So for each combination of three nucleotides, we get an amino acid, and by the time an entire gene has been read, we get either an entire protein or an entire subunit of a protein.
From proteins, we get pretty much everything else. Proteins make up skin and hair; they give our bodies structure; as enzymes, they catalyze reactions like digestion or hormone creation; they fight off diseases; and act as messengers, among many other things. Without protein, fats, sugars, nucleic acids, vitamins, and minerals would all be useless, because we would have no way to use them.
So, in summary:
DNA structure
Nucleotides -> genes -> DNA helixes + histones and some condensing -> chromosomes
How DNA works
DNA -> mRNA -> ribosome -> amino acids -> protein -> you
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