DNA: The code of life

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About the author: Maria Virginia Riquelme Breazeal is a PhD student in Civil and Environmental Engineering at Virginia Tech. Check out her profile on the VTSuN student page.

Are you alive?

The intuitive response might be “well yes, of course!” but do you REALLY know what being alive means? I invite you to ponder this question while I tell you a little bit about the code of life called DNA. First of all, having DNA does not necessarily mean that you are alive. However, if you are a human on Earth, then you MUST have DNA. Viruses, for example, may have DNA but are not considered to be alive because they are not self-sustaining. They require a host (in many cases human) in order to replicate and disseminate. This means that without a host, viruses are as alive as a rock. Here are a few interesting facts (and some of my own questions) regarding DNA:

• DNA is in ALL life on Earth, without exception (unless, possibly, aliens from a far away planet who may have evolved using a different coding system – you never know!)
• Although humans share 99% of their DNA, the parts that are different are a kind of “fingerprint” that is unique for everyone.
• DNA contains the code for its own expression, replication, and sometimes transfer

o   Wait a minute! Then who or what controls DNA? Does that mean that DNA controls itself?

• Although genes may predispose us to experience certain diseases, our DNA is “not a genetic sentencing” as proposed by Psychoimmunologist Dr. Mario Martinez and strongly supported by Dr. Richard Davidson’s research [1].

o   What this means is that our DNA expression can be modified by exercising more, laughing more, loving more, giving more, etc. (and also the opposites for better or for worse).

o   Wait another minute! That means that I can control my DNA? But doesn’t my DNA make ME?

Crash Course on DNA

I like to think of DNA as the code for the expression of life. But this definition implies that life is more than what is coded by DNA, so here is a more objective definition: Deoxyribonucleic acid, better known as DNA, is a molecule that encodes all genetic information of life. DNA is composed of only four basic building blocks called nucleotides (A, T, C, and G). Nucleotides are arranged in a particular order or “sequence” to make up the genetic instructions that give each living being their characteristics and functions.

So, why is it that if every cell in our bodies has the same exact DNA code (or “genome”) some cells look and behave differently than others? Why doesn’t my tongue beat like my heart or my ear look like a liver?

It is all a very complicated but elegant dance of chemistry. In humans, this dance starts when the egg and the sperm meet and exchange their DNA, and it begins with a cascade of chemical reactions that ultimately make up how you are physically expressed as life. In the beginning, a group of genes (DNA segments with a specific function) may become expressed until concentrations are high enough to trigger the expression of other genes and so on. In this way, cells in different parts of the body express different genes, which makes them look and behave differently than others. In the same way, the environment in which we live, the things we eat, the things we see, the movies we watch, the air that we breathe, and everything around us has the power to trigger the expression of some genes and/or repress or silence others.

But how exactly is DNA expressed?

Before DNA expression can be explained, it is important to briefly describe two other important classes of biological molecules that make life possible: RNA and proteins. RNA, or ribonucleic acid, is a close cousin of DNA and it is complementary to it. DNA and RNA look a lot alike. RNA is also composed of four building blocks, which are A, C, G, and U (instead of T). Also, unlike DNA, RNA is single stranded.

Proteins are the next essential piece of the puzzle. Simply put, proteins are the “worker” molecules, and their purpose is to facilitate almost all of the chemical reaction that take place in your body, like breaking down the food that we eat, identifying germs, etc. So, now that we know the three main biomolecules of life (DNA, RNA, and protein) we can describe life. The secret, which scientists call the “Central Dogma of Biology,” is that DNA codes for RNA, and RNA codes for proteins. Well, in reality you need all of them to make all of them (kind of like the chicken and the egg paradox), so how the chain reaction started in the first place is somewhat of a miracle.

Sneak preview: DNA in nanoscience and Environmental Engineering

Now that we are all experts at DNAing (if you can make Googling a verb, why can’t I do it with DNA?), we can discuss some of science’s interesting uses of DNA. Actually, DNA is a very important molecule in almost all fields of science. Nowadays it has become possible to sequence, modify, synthesize, and control DNA in many ways, so scientists are in the process of developing new ideas for finding, curing and preventing diseases, targeting disease-causing (pathogenic) microorganisms, identifying people, germs, and other life, etc.

A little (way way waaaaaay) closer to my professional field, is the use and application of DNA for understanding environmental bacteria and antibiotic resistance genes, which are the genes that help bacteria survive in the presence of antibiotics. For example, students in Dr. Amy Pruden’s lab at Virginia Tech extract DNA from drinking water, wastewater, soil, rivers, and other environmental sources to understand the origin, distribution, and interactions between bacteria (good and bad) and antibiotic resistance genes. This can help improve water treatment strategies and prevent the spread of disease and superbugs. Some of Dr. Peter Vikesland’s and Dr. Linsey Marr’s students are using short chains of DNA molecules called aptamers to develop nanosensors that can identify disease-causing bacteria, viruses, and antibiotic resistance genes in the environment in just a few minutes! Aptamers are very cool molecules with many potential applications, and they will take the spotlight on my next blog post.

Reference: 1. Kaliman, P.; Alvarez-Lopez, M. J.; Cosin-Tomas, M.; Rosenkranz, M. A.; Lutz, A.; Davidson, R. J., Rapid changes in histone deacetylases and inflammatory gene expression in expert meditators. Psychoneuroendocrinology 2014, 40, 96-107.

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