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Go to Brilliant.org/SciShow to learn how you can take your STEM skills to the next level! [♪ INTRO]. DNA is central to biology as we know it.

On a big level, it shapes species and how they evolve over generations. And on a small level, it’s the code that keeps your body going day in and day out. But getting to the point where we understood that took years of research.

By the 1940s, the most we knew was that genetics involved compounds called nucleic acids, but we didn’t know which ones were important, or in what proportions. And for that knowledge and much more, we have to thank Marie Maynard Daly. If you’ve heard anything about Marie Daly, it’s probably about her work on atherosclerosis , a.k.a. clogged arteries.

By feeding rats high-cholesterol diets, she and her colleagues observed a connection between cholesterol, high blood pressure, and arterial lesions. And while that might sound obvious to us now, at the time, it was groundbreaking and served as a foundation for researching other high-blood-pressure diseases.  But this wasn’t anywhere near where Daly’s career ended, or began! In graduate school, she had studied the substances involved in digestion, like amylases, which break down complex starches found in things like corn and potatoes.

And when she graduated in 1947, she became the first Black woman in the United States to receive a Ph. D. in chemistry. But she didn’t limit herself to amylases and heart disease.

She also made outstanding contributions to the study of DNA. In 1948, she joined a lab run by Alfred Mirsky, a molecular biologist, to study the cell nucleus and what was inside it: that is, DNA.  As part of their work, they were trying to figure out which nucleic acid bases, or building blocks, were in DNA, and if the ratio of them was the same across all samples. To do that, they extracted the DNA from different animals and plants, and Daly separated them out and analyzed them using a starch column.

Starch columns work because the compounds in DNA have different properties. Some nucleic acids stick really strongly to the starch column, and others don’t. So, when you run solvents like alcohol over the whole setup, some of the nucleic acids flow away pretty quickly, and others move along kind of slowly.

So, ultimately, the nucleic acids get separated and organized by their chemical properties. Here, after Daly separated everything out, she concluded that only the DNA bases adenine, guanine, thymine, and cytosine were present in significant amounts. Or today, you might hear them as A, G, T and C for short.

And she was right!  I mean, there’s a reason you still hear about these bases in biology class:. They’re the main building blocks of DNA! And beyond that, this was also the nail in the coffin for another hypothesis at the time, which said that there were tetranucleotides, or compounds where A, T, C, and G were all fused together.

Daly’s research showed that that just wasn’t possible. And this wasn’t her only contribution to genetics, either. She also made discoveries that helped us understand not just what DNA is made of, but how that genetic code, or genome, gets translated into proteins that run our bodies.

See, here’s the thing about genomes: They contain all the instructions our bodies need to make proteins, which then go on to do all kinds of jobs. But how do our bodies know when to read which part of the genetic code? It turns out that the answer comes down to structures called histones.

As part of her work, Daly isolated the histones from different animals to determine what they were like, and what they did. One of her major findings was that there were different kinds of histones. Some had a lot of the amino acid lysine in them, and others had a mix of lysine and another amino acid called arginine.

And this turned out to be a big deal. Since then, researchers have discovered that histones with these amino acids are important for helping the cell figure out which parts of the genome to read. When the body needs a certain protein that's encoded by that section of DNA bound to a histone, another protein comes along and modifies an arginine or lysine with a specific molecule.

It’s kind of like adding a tag onto certain parts of the genome that says, “Hey, it’s time to read this gene, because we need this protein ASAP.” This process is foundational for how your body works. And Daly’s discovery about these lysine- and arginine-rich histones are now considered fundamental in cell biology. So, from heart diseases to DNA and histones,.

Marie Maynard Daly laid the foundation for key science discoveries in medicine, genetics, and beyond. Today, we take most of them for granted, but genetics as we know it is only possible thanks to her work. If you want to keep learning more about topics like this, you might like Brilliant’s course The Chemical Reaction.

It’s all about learning to predict what happens in chemical systems, but without needing to memorize a bunch of equations or quantum mechanics principles. Instead, it’s based on hands-on, interactive learning, and the course comes with all of Brilliant’s usual diagrams, guided problems, and more to make it easy to follow.  If you want to check it out, you can go to Brilliant.org/SciShow. And if you sign up, you’ll get 20% off the annual Premium subscription. [♪ OUTRO].