Explainer: What are proteins?

These tiny machines perform tasks for cells throughout the body


Many foods, such as the ones shown here, are rich in protein. In the body, proteins act as biochemical machines that do the work of cells.


DNA supplies nearly each cell of the body with an instruction book on how to make tiny chemical machines. Known as proteins, these itty bitty widgets do all the work needed to help a cell survive. Some proteins carry in crucial supplies. Others take out the trash. Some send important messages. Some even fight off invaders.

Studying proteins gives scientists a better idea of how cells are supposed to work and what happens when they malfunction.

Cells build proteins by piecing together basic chemical building blocks known as amino (Ah-MEE-no) acids. Small strings of up to 100 amino acids are known as peptides. They can join forces to become a complete protein. But peptides can also function on their own, often working as messengers to carry signals throughout the body.

Human cells build their peptides and proteins from a standard kit of only 20 different amino acids. But cells can string these amino acids together in countless ways. The result is a remarkably diverse catalog of biological materials.

This is the chemical structure of pepsin, a large molecule that breaks down proteins into smaller peptides. The pepsin molecule is itself made of peptides, here shown in different colors.


So far, researchers have found the basic instructions — or genes — for about 21,000 human proteins. Including possible variations, though, the total number of different types could be as high as 250,000 to one million! Some proteins stick around for only a short time. Cells can then break them down and reuse their amino acids to form new proteins. Others, such as collagen proteins, provide tissues such as bone and muscle with solid supports that are built to last.

Protein isn’t just important for studying bones. It’s a vital component of our diet. It’s found in food such as eggs, meat and milk. Your body will break down the proteins in food into their amino-acid building blocks. Those blocks can then be recycled to build new proteins and new tissues, such as muscle. (That’s why bodybuilders eat so much high-protein food.) During childhood, kids need plenty of protein for the tissue-construction projects taking place throughout their bodies.

If children don’t get enough to eat — or enough protein overall — their health will suffer. But the dietary proteins in some foods, such as meats, milk and peanuts, can pack a real punch.

Bryn Nelson is a former microbiologist who now writes about science and lives in Seattle, Wash. He loves stories about medicine, microbes and the natural world. He drinks way too much coffee and has a playful dog named Piper.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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