MODULE #1: Biology: The Study of Life
DNA and Life
Our first criterion states that all life contains DNA. Now we're sure you've at least heard about DNA. It is probably, however, still a big mystery to you at this point. Why is DNA so special when it comes to life? Basically, DNA provides the information necessary to take a bunch of lifeless chemicals and turn them into an ordered, living system. Suppose, for example, we were to analyze an organism and determine every chemical that made up the organism. Suppose further that we went into a laboratory and made all of those chemicals and threw them into a big pot. Would we have made something that is alive? Of course not. We would not even have made something that resembles the organism we studied. Why not?
In order to make life, we must take the chemicals that make it up and organize them in a way that will promote the other life functions mentioned in our list of criteria for life. In other words, just the chemicals themselves cannot extract and convert energy (criterion #2), sense and respond to changes (criterion #3), and reproduce (criterion #4). In order to perform those functions, the chemicals must be organized so that they work together in just the right way. Think about it this way: suppose you go to a store and buy a bicycle. The box says, “Some assembly required.” When you get it home, you unpack the box and pile all of the parts on the floor. At that point, do you have a bicycle? Of course not. In order to make the bicycle, you have to assemble the pieces in just the right way, according to the instructions. When you get done with the assembly, all of the parts will be in just the right place, and they will work together with the other parts to make a functional bike.
In the same way, DNA is the set of instructions that takes the chemicals which make up life and arranges them in just the right way so as to produce a living system. Without this instruction set, the chemicals that make up a life form would be nothing more than a pile of goo. However, directed by the information in DNA, these molecules can work together in just the right way to make a living organism. Now of course, the exact way in which DNA does this is a little complicated. Nevertheless, in an upcoming module, we will spend some time studying DNA and how it works in detail.