Info Post #1: What Is DNA?

Info Post #1: What is DNA?

This is the first of thirteen more in-depth write-ups I have planned out for this year. The list (which is not set in stone!) can be found here.

I decided to do these as a way to get more information out to the readers here without having to delve into one specific ask or series of questions. I can imagine that these might create more questions as I go, but I’m also hoping that they will provide a resource that readers can refer back to. The general idea is to allow the series to build up in complexity, and give everyone a better understanding of these topics!

What is DNA?

This first topic is going to be relatively short, because in a couple of weeks I am going to do “what is a gene”, which will get much longer and more complicated, but I wanted some set up about the physical structure of DNA.

You might have heard DNA described in a lot of different ways. Deoxyribonucleic acid. The building blocks of life. The blueprint of You. None of these are particularity inaccurate, but I don’t think that any of them are super great descriptors of what exactly DNA is, or how exactly it goes from existing in cells to encoding entire organisms (although I am going to talk about the actual encoding part in the future).

For now, we are going to start small. Let’s only look at the actual physical structure. Here we have a DNA molecule:

image from wikimedia commons here

So beautiful! (I might be biased, but DNA is my favourite molecule- it’s elegant in both design and function.)

This can be broken down into two main parts:

The phosphate-sugar backbone (all those P’s and O’s and light blue on the outside)

The nucleobases (adenine [A], thymine [T], cytosine [C], and guanine [G]- the purple, pink, yellow and green)

I will point out the hydrogen bonds in the middle as well. Note that cytosine and guanine have three bonds between them, and adenine and thymine only have two. These molecules always bond in this pattern (A bonds to T, and C to G). If you’ve heard DNA being described as “complementary”, this is why! If you find a C on one strand, you know that you will find a G on the other (this became very important for sequencing, but we will talk about that later).

The hydrogen bonds in the middle are quite important as well. If these molecules were bonded to each other directly, it would be basically impossible to open the strand to “read” the DNA. Instead, this can be done by breaking those hydrogen bonds, and then allowing them to reform. This does mean that a mutation is much more likely in a high A-T region rather than a high C-G on, simply because A-T only has two bonds, and C-G has three. As well, quite often before a gene is encoded, there’s a long stretch of TATA- repeated (these are cleverly called TATA-boxes), so that the strand can more easily be opened and the encoded gene read. More on that when I talk about what a gene is!

And that is honestly pretty much it for DNA (I say that in jest- there is a lot more, and this is the result of a few billion years of evolution!). It’s not a terribly complicated design, which is probably why it is so immensely biologically successful.

So, there we have it: a very, very quick rundown that is mostly to get some important features pointed out before I talk about what a gene is, and how DNA encodes them on January 31st. This is hardly comprehensive, but I will get more in-depth into the structure and features then, and I didn’t want to make that info post horrendously long. Thanks for reading!