DNA—the little instruction manual that tells our bodies how to create life.
It’s everywhere around us, and even within us. And with DNA sequencing, we can take a direct look into what it contains. But why do we do DNA sequencing, and what can we learn from it?
If you’ve ever wondered why people do DNA sequencing, you can start with this simple guide.
A Primer on DNA
In order to know about DNA sequencing, you have to know some important things about what DNA is and how it works. You might’ve learned all about DNA in a classroom in high school, but here’s a quick reminder in case you forgot:
The Double Helix
The “double helix” of DNA refers to the two curving structures that wind around each other throughout the molecule. This form is what allows DNA to replicate. When the double strands of DNA are separated, each strand can serve as a template for how to rebuild the other strand.
The strands are attached to the other by a series of connections, like rungs on a ladder. These connections are hydrogen bonds between what we call the base pairs.
Base Pairs
The base pairs are made up of the bases A, C, G, and T—adenosine, cytosine, guanine, and thymine. Each rung on the ladder of the DNA molecule represents a bond between a pair of these bases.
In order to know the entire DNA code, we just have to know the base sequence of one strand. This is because each base will only pair with its natural partner.
Adenosine pairs with thymine, and cytosine pairs with guanine. (And guanine pairs with cytosine, and thymine pairs with adenosine). A sequence on one strand of DNA that goes GCAAT will pair with the sequence CGTTA on the other strand.
The Gene
Genes are important. They are the pieces that end up creating proteins, which make up so many things in your body.
People joke about having a “funny gene” or a “smart gene,” but it is true that your genes help determine who you are. While there may not be a single “smart gene,” there are genes that can serve as indicators of a disease or condition.
A gene is one section of the DNA molecule, and it’s defined by the short sequence of base pairs in that section. Nothing’s actually that short in human DNA, so when we say “short,” we mean something around 27,000 base pairs long.
What Is DNA Sequencing?
DNA sequencing is the process of figuring out the order of base pairs in a DNA segment. When we do this, we can recognize a certain gene-based on whether a piece of sequenced DNA matches that gene’s code. We can also find segments of DNA that can turn genes on or off.
We can also determine whether there are any anomalies in that code. This is important for tracking the risk of disease.
Today, much of the technology used for DNA sequencing has been influenced by the Human Genome Project, a massive effort to sequence all 3 billion base pairs of human DNA. The project was meant to take 15 years, and in the end, it took only 13. Because the project was so large, it led to a multitude of new possibilities, including the commercial DNA sequencing people do today.
What Is the Process?
The method used to accomplish DNA sequencing is one that replicates natural processes. Scientists use enzyme DNA polymerase, the same enzyme that’s used by the body in DNA replication, to bind to a single strand of DNA and create the other side of the equation.
Then, the scientists run the DNA through a gel to separate the DNA fragments by size. This is a process called gel electrophoresis, and it works based on how quickly the DNA can move through the gel.
Smaller pieces move through faster, so they will cover more distance in a set amount of time. By running DNA through this gel and seeing how far each fragment has traveled, scientists can identify each piece by its size.
At the time of the Human Genome Project, a style of DNA sequencing known as Sanger sequencing was automated in order to meet the volume demands of the project. These days, we have something even better: next-generation DNA sequencing.
The main difference between Sanger sequencing and next-generation sequencing is the output rate. While Sanger sequencing works in a back-to-back way, the next-generation method allows researchers to sequence many fragments in parallel. This multiplies the potential output of a single run.
Why Do We Do DNA Sequencing?
These days, given the new methods and lower costs, there is a multitude of purposes for sequencing DNA. Among these are:
Tracking Epidemics
When there is a virus outbreak, it’s important to know the structure of the virus and how it interacts with the human body. By doing this, we can better track the progression of the disease. DNA sequencing was used to track the Ebola outbreak in the recent past, and it is being used for COVID-19 today.
In the case of COVID-19, it’s not an epidemic we are dealing with, but a pandemic. Scientists are using DNA sequencing to assist contact tracing methods when new cases start to appear in their country. This can be used to determine the origin of outbreaks as the world tries to avoid a second wave.
Finding Better Treatments for Cancer
Using new methods, it’s possible for a cancer patient to have their tumor sequenced in order to see what genetic mutations are involved. This way, they can choose a treatment plan that might have a better chance of working with their specific mutations.
This method of choosing treatment based on a specific genomic sequence is still just a theory, but it’s a strong one. The National Cancer Institute is now working on a project to determine whether this theory holds up.
Learning About the Past
DNA sequencing has become a useful tool for evolutionary biology. Researchers already use a variety of physiological methods to determine whether two creatures share a common ancestor. Being able to sequence DNA from various animals (including humans) has become an illuminating new step in the process.
A New Era of Understanding DNA
So why do we do DNA sequencing—beyond the simple desire to understand DNA in a way we haven’t been able to before? Well, this technological marvel has opened up new uses for DNA sequencing to keep growing.
This is a new era of understanding DNA, and now you know a little more about how it all works together.
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