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DNA exists in every living thing except some viruses. DNA is a long molecule that builds everything from the smallest fungus on the forest floor to the cells making the beating heart of a blue whale. The strangest aspect of DNA is that the DNA in the fungus and the DNA in the whale are not so different at all.
What is DNA made of?
The fully written form of DNA explains exactly what it’s made of! DNA stands for deoxyribonucleic acid. If that sounds like a chemical mouthful, don’t worry! The building blocks of DNA are more important than the complicated chemical names. DNA is structured like a twisted ladder. It has two strands that resemble the two poles of a ladder, and many rungs which connect the two poles. The poles are made of a special sugar, deoxyribose. Deoxyribose is attached to a compound known as phosphate (a combination of phosphorus and oxygen). This is the strong scaffold for the important rungs – the sugar-phosphate backbone. The phosphate tethers adjacent sugars together, like an axle connecting identical wheels. Each half of the rung can be one of four nitrogenous bases, known as A, T, G, and C. These are ring-shaped molecules that contain a lot of nitrogen. The bases can be mixed and matched however you want, but there’s a catch—the base on one half of the rung determines the base on the other.
G can only correctly pair with C, and A can only correctly pair with T. Chemical bonding between the pairs unites both sides of the ladder. This means that the structure on one half of the ladder predicts the structure on the other half of the ladder. If you know one side has A, the other side must be T!
What does DNA do?
To understand what DNA does, it’s important to understand what we are made of. Humans and all living things are made up of carbohydrates, proteins, and fats. You may recognize these terms from labels on food, like the backs of cereal boxes. Everything we eat is made of plants and animals, which are also made of the same three things!
Most important structures in bodies are made of proteins. Proteins are massive chains that can take a huge range of forms. Each link in the chain is an amino acid. For a long time, biologists actually thought that proteins were the blueprint of life!
DNA holds all the information necessary to make all the proteins in a body. Half of the DNA ladder is known as a strand. A strand can be read from end to end like a long string of letters—AAA, ATT, CGC, CGGGCCCATA, and so on. In fact, the human genome is 3,200,000,000 letters long. Imagine all these letters together making a book. You have a little cardboard cutout just three letters wide, and the rest of the book is invisible to you. Each view from the cardboard cutout reveals a sequence: ATA, GGC, GCA, and so on. This three letter sequence is known as a codon.
This is how cells read DNA. The sequence of three bases determines what the amino acid will be. Then, the sequence of amino acids determines what the protein will be! The letters are organized into chapters, with each chapter making one protein.
When the chapters in the book are read together, we have all the information we need to make the organism! Just by ordering bases in a sequence, DNA can be the blueprint for life.
How does DNA replicate?
It’s important for information to stay consistent from cell to cell, or from the parent to the offspring. If the DNA changes each time, the proteins that form will be different. This means that something could go wrong, or that something might not work at all. With 3.2 billion letters to copy, how does DNA get it right?
The answer again lies in the sequence of letters. If you have a single ladder made up of two complementary halves, how can you make two new ladders? The first option is to make a new ladder from scratch. Then, you have one old ladder and one completely new ladder. The second option is to take sections from the first ladder, and use them to build your second ladder. At the end, you have two ladders that are each a mishmash of old and new. The third option is to use each half of the ladder to make a new one. Then, you have two ladders which are exactly half old and half new!
Since the pairs between bases are so rigid, the order of one half of the ladder tells us the order of the second. One half of the ladder is the template for the other half!
“DNA is the blueprint of life” is a sentence you might hear often, but it’s hard to understand exactly why this is the case. The answer lies in the sequence of bases, which allows DNA to code for proteins, and to copy itself for each cell and each generation to come!
Glossary
Amino Acid: The building block of a protein
Codon: A set of three bases in a DNA sequence
Deoxyribose: A ring shaped sugar that has one less oxygen than ribose
Molecules: A collection of chemical elements bonded to each other
Nitrogenous Bases: Nitrogen-rich, ring-shaped molecules that make up DNA
Protein: A biological molecule made of carbon, nitrogen, hydrogen, and oxygen
Template: The guide for one strand of DNA based on the other
Flesch Kincaid Grade Level: 5.6
Flesch Kincaid Reading Ease: 76.8
References
https://www.ncbi.nlm.nih.gov/books/NBK21134/
https://www.nature.com/scitable/topicpage/discovery-of-the-function-of-dna-resulted-6494318/
https://www.nature.com/scitable/topicpage/semi-conservative-dna-replication-meselson-and-stahl-421/
https://www.nature.com/scitable/topicpage/dna-is-a-structure-that-encodes-biological-6493050/
Yamini Srikanth: Author Yamini's (he/they) interests lie in environmental education, science communication and trying to build a better world. When not languishing in front of his laptop, they can be found outside, poking at any insect, bird or plant. They love making science accessible, especially to those who aren't encouraged to pursue it. Yamini hopes that the young women who read Smore love learning from their articles and get just a little bit more excited about science! View all posts
