It’s a Bird, It’s a Plane, No It’s…

When we last left off our mild-mannered molecule (aka DNA), we had a central question – how does it contain information.  That’s an important word information – it means that in some way or other DNA is giving instructions for how to build proteins.  Or, more exactly, DNA is giving instructions to the 20 different types of Amino Acids on how to properly organize themselves to form a protein.

So, what’s the secret? How does DNA do it?

Are you ready?  [Drum roll please]

DNA is a code!

Ta Da.

Not as impressed as you thought you would be.  Well, let’s see if we can change that.

The Fastball of Life

First things first, let’s understand what we mean by a code.  Think of a code as a type of language – a means of communicating in a symbolic manner.

For instance, in baseball – ever wonder how a pitcher knows when to throw a fastball or a runner decides to steal second (okay, I never really wondered that either – in fact, I don’t even watch baseball – but for the sake of this conversation let’s pretend that we care).  They use signs and symbols to speak without speaking, to communicate without words.

Here is a short example of how it works:

Well, and here is the wondrous part, DNA seems to be the chemical equivalent of telling a pitcher to throw a fast ball or a runner to steal second base.

DNA, it turns out, is made up of a series of chemical ‘signs’ or ‘symbols’ which indicate which Amino Acids to use and in which order.  In particular, there are  four different chemicals at the heart of the DNA molecule and the order of those chemicals indicates which Amino Acids to use.  Those chemicals are represented by the letters A, C, G and T – the first letter of the names of each chemical (we won’t worry about the particular names for now, it will just confuse us).

To get an understanding of how this works, let’s imagine that we have a strand of DNA and the first three chemicals in that strand are in the in the following order — A, C and T.  Through a process called translation (which we’ll discuss later), that will mean that the first Amino Acid in the protein sequence will be Threonine (again, don’t worry about the names, just the concept).  Now, let’s imagine that the next three chemicals are GTG – that will ‘translate’ into Valine.

At this point, our budding protein has two Amino Acids – Threonine and Valine – in a particular order.  Now this process can go on for hundreds of Amino Acids – each Amino Acid corresponding to a particular set of 3 DNA chemicals.  It is thus the sequence of these four different chemicals that determine which Amino Acids are used and in which order.

Let’s See What’s Going On

Now, some of your brains may be spinning right now – so, as always, here is a video (or two) to help you conceptualize what it is that we are talking about.

The Structure of DNA

First of all, let’s take a look at the structure of DNA:

How DNA Works

And now let’s get a basic introduction into how DNA actually works.

Note, I know we have not mentioned mRNA yet and the following video does, so a brief introduction is in order. Think of mRNA as a xerox copy of the instructions that are in DNA. You see, DNA is in the nucleus of the cell and the protein is made outside of the nucleus. So, what (kind of) happens, is that those instructions are ‘xeroxed’ and sent out of the nucleus of the cell. The copied instructions are then translated into Amino Acids.

So, with that said, here is a basic idea of how this all works:

The Cell’s Catcher

So DNA is like the cell’s catcher – sending signals which indicate which Amino Acids to make and in which order. We still have not learned how the cell knows which sequence of DNA to copy or how it actually reads these signals. We’ll get to all of that in due time.

For now, though, we should marvel at what we have seen. DNA is basically a recipe book for life. It has coded information that tells the cell how to build all of the proteins that we need to live and function.

This fact has profound scientific, theological and philosophical implications, which we will begin to explore shortly. But first, let’s see see how amazing this molecule really is.

We’ll do that in the next post.