Science Fundamentals: DNA

After my series on Scientific Literacy (please go check that out), I wanted to do a series on the fundamentals of science. Hopefully these quick explanations of science terms and processes are helpful, and are part of the groundwork for your scientific literacy. If there are topics that you would like me to cover, please let me know in the comments. I have a PhD in microbiology/biochemistry, but I am happy to do some digging into topics that I don’t deal with everyday.

This Science Fundamental is on DNA. It is probably a term that you are familiar with in common language, but how much do you know about the science behind those 3 letters?

What is DNA?

DNA (deoxyribonucleic acid) contains all of the instructions required for the growth, development, and reproduction of an organism.It is a polymer, a term you might be more familiar with in plastic. ‘Poly’ just means many, and ‘mer’ is a thing. So a polymer is something that is made of ‘many things’. DNA is two long chains of nucleic acids (the ‘mer’ in polymer for DNA). These two long chains wrap around each other forming the iconic double helix. If this doesn’t come to mind, think of a ladder that twists like a spiral staircase as it goes up. The backbone of the helix, or the sides of the ladder, is sturdy made of sugar to sugar links. It isn’t table sugar, but it’s apparently sweet and can be used in lemonade ( who knew right?) The rungs of the ladder, where you put your feet, are the ‘bases’. With minor exceptions, there are only four bases that make up all of DNA. These are represented by single letters that correspond to the common name, they are A, C, T, and G. These four bases pair together in specific ways. When one side of the backbone has an A, the same spot on the other has a T. When one has a C, the corresponding part is a G. Every time. In this way, the two chains, or sides of the ladder contain the exact same information.

What does DNA do?

It might be helpful to think of DNA as a library, where all of the information is stored. This information is everything that makes you, well, you. Areas of the DNA that directly affect your characteristics, like appearance, are called genes. You have genes that made you have two eyes, different genes decided the color of your eyes, and still different genes influenced your eyelash length. With genes controlling or influencing  every part of your body, inside and out, you would think that our DNA would be loaded with them right? Humans are estimated to have about 30,000 genes. That’s a lot. However, 98% of the human genome (all of our DNA) does not contain genes. We used to call all of that DNA ‘Junk DNA’, but now we understand that some of it actually helps the 2% of the DNA with genes. Genes are able to define or affect us, because they send messages to factories in our cells to produce proteins. If DNA is our library, then the messenger is RNA. I’ll write up a post for RNA as well, but for right now think of it as DNA’s messenger, like WhatsApp or iMessage. DNA sends a message using RNA to protein factories in our cells, and using that message, the factories make specific proteins to do what the DNA wants. I’ll write up a post on proteins as well, but for now, they are the do-ers. Proteins get stuff done.

How do we make more DNA?

All of this is really cool, but what happens when we need to make more DNA? Well, because the bases always match up in the same way, each side, or chain, of the DNA carries all of the information. So a protein, called a helicase, pulls the two chains apart. Then a second protein, called a polymerase follows the helicase and remakes the DNA by adding the right base to match the DNA being copied. We call this replication. Most of the polymerases have the ability to catch mistakes, called proofreading. So if it puts the wrong base with the DNA, it knows to remove it. In this way, we get really good copies of DNA. Since the DNA was split into the two chains, and a polymerase copied both, at the end of replication, we have two DNA that are exactly the same.

Hopefully this brief introduction to DNA is helpful. If you find it useful, please let me know. Drop me a line. If you have any suggestions for future Science Fundamentals, then let me know. I’ll be happy to look at specific topics for you. 

The next Science Fundamental will be on Polymerase Chain Reaction or PCR. This topic has been in the news quite a bit with the PCR test for COVID-19 being the golden standard for tests. After that, the plan is to look into the rapid antigen tests and then do a comparison. So please, stay tuned. 

Glossary

1. DNA

   1. Deoxyribose Nucleic Acid

2. Polymer

   1. A larger product made up of smaller products 

   2. Name: Poly (many) plus mer (item or thing)

3. Nucleic Acid

   1. Organic compounds that make up genetic material 

4. Gene

   1. A section of DNA that encodes RNA to make a functional protein that alters the organism 

5. RNA

   1. The messenger nucleic acid. Takes messages from DNA to protein factories. Has other functions as well. 

6. Protein

   1. A bio molecule made up of amino acids. Usually has an important function

7. Helicase

   1. A protein that unzips DNA

   2. Name: Helix (as in the double helix of DNA), plus ‘-ase’ which is the general ending of a name for an enzyme (a protein that does something, the do-er of the do-ers)

8. Polymerase

   1. A protein that replicates DNA

   2. Name: Polymer (see above) and -ase ( general protein ending)