Genomics101: A Brief Introduction to DNA

Series Overview: Hi, my name is Shari and like the majority of our readers I don’t have a degree in science. What I do have is almost a decade of experience working closely with Genetic Counselors, and a passion for sharing genomic information in an approachable and easy to understand way. This passion was developed early in my career, fueled by my quickly building frustration about the over-complicated resources I found during initial attempts at self-guided learning. Genomics 101 is a blog series by GenomicMD that aims to be a solution to that frustration for others. By breaking down the complex language surrounding this field, we hope to empower people (like you!) to be more informed about how genomics can affect their healthcare journey.

Genetics, Genomics, and DNA, oh my! Genomics is a field that has a TON of highly complicated scientific words and phrases that all seem to mean the same thing – or do they? One of my biggest pet peeves when looking up genomics terms is that the definitions tend to circle back on themselves, which can be incredibly confusing. Take, for instance, the definition of “genomics” from the Oxford dictionary: 

Okay… but what exactly IS a “genome”? Looking THAT term up tells us that it is:

But… What's a gene? What do they mean by “genetic material”... and why do I suddenly feel like I know LESS than I did before? 

Unfortunately, trying to understand genetics sometimes feels like it’s reserved for those with a specialized scientific background – which simply isn’t the case. Oftentimes it’s the teacher, not the material, that leaves us confused by the details. That said, let’s see if we can break it down step-by-step to start building a foundation of genetics knowledge from the ground up. 

The first term that anyone learns when researching genetics is usually DNA, which stands for “deoxyribonucleic acid” (trust me, you don’t have to memorize that). DNA is a material found inside the nucleus, or the control center, of a cell – which is the smallest unit of an organism that can live on its own. In most living things, DNA carries all of the instructions needed for their development and function. As you might recall from early science classes, it is made up of 2 very long strands that resemble a twisted ladder often called a ‘double helix’. Think of it this way: if your body was a set of encyclopedias, your DNA would be the written words on each page that explain all of the information about how you were built including your hair and eye color, how tall you are, and even whether you are more at risk for certain diseases than others. The ‘alphabet’ that makes up this written language in your DNA is made of 4 specific compounds (often referred to as nucleotides or bases): adenine (A), thymine (T), guanine (G), and cytosine (C). These chemicals run along each strand or “leg” of the DNA ladder, and pair with each other on opposite ends, making the “rungs” or base pairs. The order of these base pairs determines the meaning of the information in that part of the DNA molecule, just like the order of each word on a page determines the meaning of a sentence in an encyclopedia. See the image below for a visual reference on the structure of our DNA. 

Now that we’ve defined DNA and cells, let’s ‘zoom out’ a bit and explain some more terms associated with how DNA is structured within our bodies. If we imagine our body is made of encyclopedias again, and that our DNA contains the alphabet that spells out the sentences inside of it, then our chromosomes would be individual books in the set, and our genes would be chapters inside of those books. Since DNA is a very long string of chemicals bound together into the double helix, if it was left to free float around the cell it would be far too long to fit and incredibly easy to damage. Chromosomes are the “X” shaped structures inside humans that keep our DNA tightly wound up so it can stay protected inside the nucleus of our cells. Each of these chromosomes is organized into little sections called genes, and each of these genes carry a specific set of instructions for a certain part or function of the human body. 

Keeping with our previous analogy, let’s wrap this blog post up by re-defining some of the words that we tried to learn via the Oxford dictionary earlier. If we now understand that our DNA is the set of instructions for our body that are organized via an alphabet (nucleotides or bases), into individual books (chromosomes) and separated into chapters (genes); then our genome would be the entire set of encyclopedias itself or the entire set of DNA in our bodies. That means that genomics is the study of the entire genome and when the term genetic material was mentioned in the definition above, they were just referring to sections of the genome itself – such as a part of a gene, an entire gene, or a piece of a chromosome. 

Thank you for joining me on this journey to break down some of the complicated language surrounding the structure of DNA. Many sources make this subject seem far more difficult to grasp than it truly is, but if I can understand these concepts I know that you can, too! Please join me for our next chapter in this series, where we will dive into more complex terminology and continue to build a foundation of genomics knowledge bit by bit.

Blog Glossary:

DNA - The material inside cells that carries the information responsible for the development and function of all living things

Double Helix - The visual structure of DNA. It is made up of 2 linked strands that wind around each other and resemble a twisted ladder

Nucleotides/Bases - Compounds that sit on opposite strands of the DNA double helix and form bonds with one another. These bonds create the ‘rungs’ on the DNA ladder called base pairs. There are 4 of these chemicals which are listed in the definition below

Adenine/Thymine/Guanine/Cytosine - The compounds that makeup base pairs, or the “alphabet” of your DNA. The order of these determines the ‘spelling’ of your DNA.

Cells - The smallest unit of an organism that can live on its own, it is made up of 3 main parts: the cell membrane (the ‘fence’ that holds everything inside the cell), the nucleus (the most central part of the cell which contains DNA), and the cytoplasm (the fluid in the cell surrounding the nucleus).

Genes -  Sections of our chromosomes that contain information that provides instructions for the functions of our body.

Genetic Material - This term refers to any part of a cell that contains a portion of DNA, such as a piece of a gene, a whole gene, or even an entire chromosome.

Chromosomes - Structures in the human body found in the nucleus of cells made of tightly wound DNA.  

Genomics - The study of the complete set of DNA (including all of its genes) in a person or other organism.