protein

American  

[proh-teen, -tee-in] / ˈproʊ tin, -ti ɪn /

Also proteid

noun

1. Biochemistry. any of numerous, highly varied organic molecules constituting a large portion of the mass of every life form and necessary in the diet of all animals and other nonphotosynthesizing organisms, composed of 20 or more amino acids linked in a genetically controlled linear sequence into one or more long polypeptide chains, the final shape and other properties of each protein being determined by the side chains of the amino acids and their chemical attachments: proteins include such specialized forms as collagen for supportive tissue, hemoglobin for transport, antibodies for immune defense, and enzymes for metabolism.

2. the plant or animal tissue rich in such molecules, considered as a food source supplying essential amino acids to the body.

3. (formerly) a substance thought to be the essential nitrogenous component of all organic bodies.

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adjective

1. Biochemistry. of the nature of or containing protein.

protein British  

/ ˈprəʊtiːn /

noun

1. any of a large group of nitrogenous compounds of high molecular weight that are essential constituents of all living organisms. They consist of one or more chains of amino acids linked by peptide bonds and are folded into a specific three-dimensional shape maintained by further chemical bonding

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protein Scientific  

/ prō′tēn′ /

1. Any of a large class of complex organic chemical compounds that are essential for life. Proteins play a central role in biological processes and form the basis of living tissues. They consist of long chains of amino acids connected by peptide bonds and have distinct and varied three-dimensional structures, usually containing alpha helices and beta sheets as well as looping and folded chains. Enzymes, antibodies, and hemoglobin are examples of proteins.

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Closer Look

Proteins are the true workhorses of the body, carrying out most of the chemical processes and making up the majority of cellular structures. Proteins are made up of long chains of amino acids, but they don't resemble linear pieces of spaghetti. The atoms in these long chains have their own attractive and repulsive properties. Some of the amino acids can form bonds with other molecules in the chain, kinking and twisting and folding into complicated, three-dimensional shapes, such as helixes or densely furrowed globular structures. These folded shapes are immensely important because they define the protein's function in the cell. Some protein shapes fit perfectly in cell receptors, turning chemical processes on and off, like a key in a lock, whereas others work to transport molecules throughout the body (hemoglobin's shape is ideal for carrying oxygen). When proteins fail to take on their preordained shapes, there can be serious consequences: misfolded proteins have been implicated in diseases such as Alzheimer's, mad cow, and Parkinson's, among others. Exactly how proteins are able to fold into their required shapes is poorly understood and remains a fundamental question in biochemistry.

Other Word Forms

• nonprotein
  noun
• proteinaceous
  adjective
• proteinic
  adjective
• proteinous
  adjective

Etymology

Origin of protein

First recorded in 1835–45; from German Protein, from Greek prōte(îos) “primary” + German -in -in ²; replacing proteine, from French; cf. proto- ( def. )

Explanation

Protein makes up your nails, your hair, and the egg on your plate. This nitrogenous substance we call protein consists of chains of amino acids and is necessary for life functions. The linguistic origins of protein — from the Greek proteios, meaning “first place” or “primary” — are fitting for a substance that is one of life’s chief components. Although protein is a word often heard in labs and biology classes, it has everyday context too, particularly in the kitchen. Protein-rich foods like eggs, cheese, meats, peanuts or beans are an essential part of good nutrition.

Example Sentences

The El Segundo maker of plant-based proteins that look and taste like meat changed its website and social channels last week to reflect its new full name: Beyond the Plant Protein Co.

From Los Angeles Times • Mar. 10, 2026

Professor Payne is also set to lead the newly announced Australian Research Council Centre of Excellence for Advanced Peptide and Protein Engineering.

From Science Daily • Feb. 6, 2026

The firm is also pivoting towards health-focused products, with the launch of Doritos Protein later this year.

From BBC • Feb. 3, 2026

Witness the cereal aisle, home now to Cheerios Protein, Nature Valley Protein Granola and many more protein-infused brands.

From The Wall Street Journal • Jan. 14, 2026

But all I can talk her into is taking the Pure Protein sports bar I always carry in my bag in case my sandwich lets me down.

From "Nickel and Dimed: On (Not) Getting By in America" by Barbara Ehrenreich