The instructions in DNA are written in a simple alphabet that has just four letters—A, T, C, and G. Now, of course, these are not really letters. Instead, they are molecules called nitrogenous bases that are part of a larger molecule called a nucleotide that forms the basic building block of DNA. The letters of the alphabet are really just abbreviations for the nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).
The function of DNA is tied to its structure, which is helpful to review to understand its function. As stated above, the basic building blocks of DNA are nucleotides. These nucleotides are composed of a five-carbon sugar, a phosphate group, and a nitrogenous base. The sugars and phosphates link the nucleotides together to form each strand of DNA. When two strands of DNA come together, base pairs form between the nucleotides of each strand.
Nitrogenous bases pair together in the following way: A-T and C-G. Bases interact through weak bonds, called hydrogen bonds, that can be easily broken and reformed. This is important during DNA replication. The two DNA strands must be separated before being copied, and important for a cell’s ability to read the instructions found within the DNA.
The bonds between nitrogenous bases are essential to DNA’s double helix structure, which resembles a twisted ladder. The base pairs form the rungs of the twisted ladder, and the sugar-phosphate strands form the sides.
There is so much DNA in each tiny cell that it must be condensed further to fit inside. The DNA is tightly coiled into structures called chromosomes. Humans typically have 46 chromosomes – 23 from each parent.
How Does DNA Perform Its Function?
Everyone (except identical twins) has a unique set of DNA called their genome. The nucleotides A, T, C, and G act as the four letters of the genetic alphabet. This is why everyone is unique—each person has a slightly different set of instructions leading to a slightly different person. Maybe one person has a T at a certain spot in their DNA and so has red hair, and the person with a G is blonde.
A cell reads the instructions in the DNA with something called an RNA polymerase. This RNA polymerase separates the two strands of the DNA helix and copies the DNA of one strand into a molecule called RNA.
RNA is very similar to DNA except that instead of thymine (T), it has uracil (U). So when RNA and DNA pair up, G pairs with C, and U pairs with A (the T of DNA still pairs with the A of RNA). While some of the instructions stop at the RNA stage, most go on to an additional step.
For this step, the DNA letters are grouped into three-letter words, which are then recognized as full sentences, called genes. This process can be illustrated in the following example:
Letters (nucleotides): A, C, G, T . . .
Three-letter words: “ACT,” “CAT,” “TAG” . . .
A sentence (gene): “CAT ACT TAG . . . ”
All of the possible four-letter combinations give 64 three-letter words, commonly called the genetic code. This code is read and translated into different compounds, called RNA and proteins, which do important jobs in your body. These proteins perform jobs like carrying oxygen to your cells or making the pigment that gives your eye color.
Why Is DNA Important?
DNA is important because it holds all of the genetic information that makes you, you. This information is needed for your development and survival and can be passed along to the next generation. It also influences your traits, ranging from what you look like to the food you like with lots of things in between.
Given how different you are from someone else, it might seem like everyone’s DNA should be very different from one another. Amazingly this is not the case. On average, you share around 99.5% of your DNA with someone you are not related to.
A big part of what makes you unique is found in that 0.5% of your DNA. And even though we’re overall more alike than different, everyone’s DNA tells a different story about who their relatives are and where they are from. What story does your DNA tell?
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