December 1st, 2011


Advent Science 2011

Welcome to Advent Science 2011!

Through Advent this year I am going to make a series of posts about genetics, a subject that is sadly neglected beyond all but the very basic level in high school. My plan is first to cover what a gene is and how that is related to how living organisms are made up, and then to move on to all the ways it can go wrong. Also, you will learn how Biology GCSE is for the most part a big fat lie :)

With us for Advent Science this year are pewterfish, explaining computers from scratch, and duckbunny, talking about the history of the Earth's atmosphere.


DNA is short for deoxyribonucleic acid, which does actually make some sense, because it is made of molecules of a sugar called deoxyribose, phosphates (which are negatively charged, hence "acid"), and molecules called nucleotides, which are thus named because they were first found in cell nuclei.

The deoxyriboses and phosphates alternate in a long line, chemically bonded together and onto each deoxyribose is attached a nucleotide. In DNA there are four types of nucleotide, Adenine, Cytosine, Guanine and Thymine (usually referred to by biologists simply as A, C, T and G), and it is the ordering of these nucleotides that is your "genetic code". We'll get back to *how* this ordering determines your physical makeup in a few days.

Now, the clever bit is that a strand of DNA actually consists of *two* of these very very long molecules. The two strands form a ladder shape, with he sugar/phosphate backbones as the "uprights" and the nucleotides sticking out into the middle as the rungs. This ladder will then twist up into the "double helix" that most of you will be familiar with. The even cleverer bit is that Adenine will only bond with Thymine to make a rung, and Guanine will only bind with Cytosine.

This diagram from Wikipedia should hopefully make this rather clearer:

Tomorrow, we'll look at how this makes it possible to copy old DNA to make new DNA with exactly the same sequence...

Note: questions in the comments are welcome, though they may be answered with "wait a few days" :)