DNA

Before we can explain what DNA sequencing is, we need to provide a basic picture of what DNA is - what it looks like and the parts it is made of - because DNA sequencing is based on those parts of the DNA stucture.

Think of DNA as the 'blueprint' that makes you look like you, and all your parts into all your parts - organs, bones, hair color, height, gender, skin color, every piece of you. DNA is a very tiny blueprint; just like millions of bits of information can be stored in a tiny computer part, millions of details about you can fit into your DNA. There is no part of you, no matter how large or small, that is not programmed to look that way, to 'do its job' a certain way, and to grow a certain way (age), by these details in your unique DNA. This blueprint tells your liver to look and work like a liver, tells your hair to look and grow like hair, your eyes to look and see like eyes, your joints to look and move like joints, and everything else to the smallest detail in your body.
     Below: DNA in a variety of renditions; the double helix is such a beautiful shape it transcends science and becomes art; at far right, an actual microscopic photo of a circular DNA strand.

DNA stands for DeoxyriboNucleic Acid, which is the chemical 'stuff' it is made of. Structurally, DNA is a polymer; a polymer means a larger structure that is made up of repeating parts of a smaller structure, like a brick wall is made up not just of one brick but of many similar bricks all closely joined. In the DNA polymer, those tiny repeating structures are called Nucleotides. DNA is itself so small that you can't see it with the naked eye, or even a normal microscope, you need an extremely powerful microscope; and there are millions of nucleotides making up each DNA polymer. Size-wise, it's stunning to try figure out how so much can be packed into something so small it can't be seen: a single DNA polymer is thousands of times thinner than a single human hair... yet it holds as many pieces of information (those little nucleotides) as a few entire sets of encyclopedias.

In physical appearance: if one nucleotide were a one-step ladder sitting in front of you, think of an entire DNA polymer as millions of these steps stacked on top of each other, stretching up into the sky farther than you can see with binoculars. I use the ladder example for a reason; DNA looks like a ladder, kind of. If you take a ladder, with the parallel side members that are joined up the middle by rungs, and you turn it to rubber so you can twist it sideways around itself like a spiral, that is roughly what DNA looks like: a long thin strand of spiralling ladder. If you slice out just one rung of that ladder, and a little bit of the side member on each side to support that rung, that one unit can be called a nucleotide, and the millions of those together form the entire DNA polymer, which is commonly called by its more descriptive name, a DNA Strand.

You'll also commonly hear the DNA strand referred to as a 'double helix'. Again, this is a visual-description term: if you cut a ladder right down the middle, so each side is an upright member with a bunch of half-steps running up it, one of those 'sides' looks like a helix. When you reattach them again the structure looks like two helixes joined together, hence the designation double helix. At the beginning of this page I described the DNA strand as being called a DNA polymer, but technically, a DNA strand is not a single polymer, but rather a double, since each side by itself is called a single polymer strand - made up of individual nucleotide segments, which I'll describe more clearly on the next page - and joined together these two long 'half-sides' of the ladder form a double polymer strand. To avoid confusion: double polymer and double helix are the same thing - they are just two different terms describing the same item, but polymer refers to its chemical makeup and helix refers to its visual look. A strand of DNA polymer and a strand of DNA helix are the same thing, and joined together they can be a DNA strand, DNA polymer (or double polymer, technically), or double helix, etc.

So, now you have a very simplified but hopefully clear vision of what a DNA strand looks like, and you know that it is made up of repeating units called nucleotides. Let's cut into a DNA strand and take a closer look at those nucleotides, because those little units are what DNA sequencing is built upon.