DNA 101

We’ve talked about genes. We’ve learned about cancer. We’ve even hit upon microbes. But now it’s time to get down to the basics:

Let’s talk about DNA

See, DNA is the building block of life. DNA tells the body what to make, when to make it, and how to make it. Structurally, DNA is a very long string of nucleotides that is twisted into a helical shape. In all, there are four kinds of nucleotides found in DNA: Adenosine, thymine, cytosine, and guanine (or more simply A, T, C, and G, respectively). The order and frequency in which they appear gives rise to an individual’s unique DNA sequence. By reading this sequence three letters at a time, the body is thus able to carry out its day-to-day functions.

Interestingly, the amount of DNA in your cells is quite large. Astonishingly large, to be honest. If you stretched it out completely, your DNA sequence would be about 5 feet long! Now in order to fit all of that into a cell, you have to get a bit creative. The first thing that happens is that the DNA helix is wrapped two times around little balls of proteins called histones. This string of histone then forms little beads known as nucleosomes, which are then wrapped around each other into another helix (helixeption!). That helix is then folded up numerous times, until it forms a chromosome.  Below is a good visualization of it all that I grabbed from a textbook:

11_03EukDNAPacking-L

One of the results of DNA being so tightly wound is that the body can’t read all parts of the DNA sequence at any given time. Instead, the cell must unwind short stretches of DNA in order to access the DNA and read it. This means genes can be regulated by simply winding and unwinding sections of the chromosome. Scientists call this method of gene regulation epigenetics, and are currently attempting to understand how we can use epigenetics to solve genetic disorders.

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