protein

American  

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

Also proteid

noun

• proteins
  plural

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

Derived Forms

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

Inflected Forms

Nouns

• proteins
  plural

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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. )

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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

See Examples For:

protein proteins

The researchers also detected inflammation in the animals' brains, along with abnormal accumulations of a protein called alpha-synuclein.

From Science Daily ● Nov. 1, 2026

When they restored the cellular cleanup process or removed synuclein protein in their experiments, the neurons were protected from damage.

From Science Daily ● Nov. 1, 2026

The process begins with a protein known as Ral, which Saltiel had previously investigated in fat cells.

From Science Daily ● Nov. 1, 2026

Their findings, published in Nature, identify a protein called claudin-4 as the essential docking point for a bacterial toxin known as BFT.

From Science Daily ● Oct. 31, 2026

First and most directly, domestic animals became the societies’ major source of animal protein, replacing wild game.

From "Guns, Germs, and Steel: The Fates of Human Societies" by Jared M. Diamond

Laboratory experiments also revealed how the chemical can interfere with the brain's ability to remove damaged proteins, leading to the loss of nerve cells essential for controlling movement.

From Science Daily ● Nov. 1, 2026

Instead of binding to claudin-4 receptors on colon cells, BFT attached to the decoy proteins.

From Science Daily ● Oct. 31, 2026

The poster child of scientific AI is the UK-based firm Google DeepMind, which in 2020 solved one of biology's biggest problems: how proteins in living things fold into their precise shapes.

From BBC ● Oct. 28, 2026

Traditionally, much of the field has focused on understanding the processes that damage the brain, including the accumulation of abnormal proteins and the loss of neurons.

From Science Daily ● Oct. 27, 2026

The one scientist they did revere, if begrudgingly, was Linus Pauling—the larger-than-life Caltech chemist who had recently announced that he had solved an important conundrum in the structure of proteins.

From "The Gene" by Siddhartha Mukherjee

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