Ask Dr. Universe – DNA

Dr. Universe: How is DNA built? – Riot, 8, Everett, WA
Dear Riot,
Pretty much every living thing on our planet—from a blue whale to a tiny ant—has something in common. We all have cells, which are the building blocks of life, and inside of those cells we have DNA. 
My friend Gunjan Gakhar, a Teaching Assistant Professor at Washington State University, was happy to help with your question.
First, she reminded me that DNA contains the instructions for living things to grow, survive, and reproduce. DNA determines everything from our eye color to our hair color to our height.  
“DNA is built like a ladder,” she said. “And if you twist that ladder, that’s what DNA looks like.”
Let’s imagine we are building a DNA ladder. We will need a few simple ingredients. First, there are sugar and phosphate.
You probably know about sugar already, but phosphate is something present in your teeth and bones that helps make you strong.
The sugar and phosphate form a repeating pattern that makes up the side rails of the DNA ladder. Of course, every ladder needs steps, or rungs, too.
If we were building a real ladder, not a DNA ladder, we would probably use a single, solid piece of material to build each step.
But in our DNA ladder, the steps are actually made of two materials, called nitrogen bases, that are strongly bonded to each other. There are four varieties of nitrogen bases that we find in DNA. Scientists call these nitrogen bases A, C, T, and G. ‘A’ always binds with ‘T’ and ‘G’ always binds with ‘C’.
By following this rule, nitrogen bases can bond to each other and the side rails to form the entire DNA ladder.
It’s the differences in these combinations of bases that give us the different traits we see across species and even in individual human beings.  
Whether you are an ant, a human, or a blue whale, you get half of your DNA from one parent and the other half from your other parent.
Another interesting thing about DNA is that your body’s cells can use your existing DNA to make even more DNA—and they do it with the help of things called enzymes.  
You produce enzymes that do lots of different jobs. For instance, enzymes in your saliva help break down food. There are also enzymes in your body that help break apart DNA and make more DNA. Enzymes can open up the DNA ladder. They are like DNA scissors that can split the ladder in half.  
As long as ingredients like sugar, phosphate, and nitrogen bases are available in the cells, each side rail of the DNA can use those ingredients to make more DNA.
If you are curious how DNA looks, perhaps you can make your very own DNA model. I might use toothpicks as bases and paper to model the phosphate and sugar, as you can see here in this DNA model activity from our friends at the American Museum of Natural History. Tell us about your DNA model sometime at
Dr. Universe