Explainer: What are proteins? | Science News for Students

Explainer: What are proteins?

These tiny machines perform tasks for cells throughout the body
Oct 3, 2018 — 4:01 pm EST
A photo of an array of protein rich foods including red meat, fish, nuts, beans, eggs, chickpeas, avacado, spinach and broccoli

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.

protein structure
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.

Power Words

(more about Power Words)

amino acids     Simple molecules that occur naturally in plant and animal tissues and that are the basic building blocks of proteins.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

collagen     A fibrous protein found in bones, cartilage, tendons and other connective tissues.

component     Something that is part of something else (such as pieces that go on an electronic circuit board or ingredients that go into a cookie recipe).

diet     (adj. dietary) The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health.

dissolve     To turn a solid into a liquid and disperse it into that starting liquid. (For instance, sugar or salt crystals, which are solids, will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water.)

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

muscle     A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.

peanut     Not a true nut (which grow on trees), these protein-rich seeds are actually legumes. They’re in the pea and bean family of plants and grow in pods underground.

peptide     A short chain of amino acids (usually fewer than 100).

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

tissue     Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

widget     In computer science, a tool built into a program or website that lets a user take action in response to information provided on screen.