What does DNA Look Like?
This is a good question. What does DNA actually look like? In this section of Genetics R Us we are going to take an upclose look at what DNA is composed of and unlock its ancient ability to store information. Let’s begin by picking up where Watson and Crick began when they started their work back in 1953.
Here’s a picture of DNA shown through an electron microscope. Remember, earlier it was stated that a picture like this is not very informative. An electron microscope cannot peer deep enough.
Therefore, a different approach must be taken. The solution is that we must gather our information about DNA through both inferring and scientific models. An inference is simply a conclusion drawn from an observation taken. For example, if you come downstairs and see your refrigorater open, and you didn’t open it yourself, then someone else opened your refrigorater. You didn’t see the person, but that doesn’t matter. From that one observation, you can correctly conclude the presence of someone else. A scientific model is simply a colorful drawing that describes a concept. For example, many of the animations that are present on my pages are models.
With that in mind, let’s get started. When Watson and Crick began their study of DNA, much was already known about DNA. It was known that DNA is composed of smaller units which are called nucleotides.
Every nucleotide is composed of a phosphate, sugar, and base. The sugar is a five carbon sugar known as as deoxyribose. You can see the five carbons in the model toward the left.
It was then discovered that the nucleotides are attached and stacked on top of each other. Here’s a nice little animation that shows you what I am talking about. Let’s now see how they are attached to each other.
How the nucleotides are attached is even more amazing. Here’s how it works. If you look closely at the top nucleotide, you’ll see that the third carbon, 3, is attached to the phosphate of the next nucleotide. The next nucleotide is then attached to it’s own phosphate through it’s own fifth, 5, carbon. The nucleotides are then attached in this manner as DNA is increased in length. Below is an example that shows you this process.
The nucleotides are attached to one another in a manner mentioned above. The result is that you have a top nucleotide with an exposed 5th, carbon and a bottom nucleotide with an exposed 3rd, carbon.
As new nucleotides are attached, the DNA grows larger in a direction which is referred to as the “5 to 3 direction” This is simply a term used to refer to the fact that a DNA strand will always have a top nucleotide with an exposed 5th carbon, and a bottom nucleotide with an exposed 3rd carbon as the DNA grows in length. The information about the sugar and phosphate componets of DNA is interesting, but is still doesn’t answer our question of how DNA can store a living organisms information. When Watson and Crick began their work, they turned to the bases that make up DNA. What if the bases of DNA somehow stored the instructions on how to build and construct a living thing? Today we know that Watson and Crick were, and still are, correct. Let’s now focus are attention on the bases of DNA.
DNA is made up of four bases. These bases are known as adenine, thymine, guanine, and cystoine. Shown toward the left are the actual bases. To make things easier for you, you can simply remember the bases as A, T, G, C. So now the question becomes this. How do the bases hold information?
As Watson and Crick began their work, they began to hint on the possibilty that if the bases were connected to each other, the bases could “hold the instructions” which are used by a cell to actually build a living organism.
What Watson and Crick began realize was that DNA had a structure very similar to two ribbons that wrap around each other. This arrangement is referred to as a double helix. An example of this is shown toward the right.
However, there was one problem. Watson and Crick couldn’t figure out which bases were connected to one another. Was adenine paired with guanine? Or was guanine paired to thymine.
So Watson then worked with models he cut from paper based on the current facts about the chemistry of the bases known at that time. He then paired different bases together to get the best fit.
After much trial and error, Watson and Crick then discovered that adenine pairs with thymine, and guanine pairs with cystoine. The result was something amazing!!! The secret of DNA had been revealed. It’s structure had been unraveled.
After this great feat had been successfully completed, a whole new science had been created. From that point on, the world would never be the same.
DNA not only contains instructions on how to build a living organisms, but it turns out to a storage vault of information that contains the secrets of our ancestors from thousands to millions of years ago. This discovery then gives information to the field of anthropology.
DNA has been used in law enforcement to capture law offenders. Because DNA holds information about a person, it be used as a fingerprint to create what is called a DNA profile. And the list goes on and on. In the later sections of Genetics R Us, we are going to look at some of the other contributions that DNA has made in other areas, including anthropology, forensics, and geneology. Before we do that, however, there is still much to cover before we get to that point. For instance, have you ever wondered what the word, genetics, means?
Simply put, genetics is the study of genes. I’m sure you’ve probably heard of the word, genes, before. And no, I don’t mean the type of jeans you wear. The basic concept of gene is very important. I mean this entire website is based on the gene. In the next part of Genetics R Us, we are going to look at the gene. Before we do that, there are few things we need to cover. So put on your thinking caps as we really are about to find out about the genetics that are us.