noun, often attributive
pro·​tein | \ˈprō-ˌtēn also ˈprō-tē-ən \

Definition of protein 

1 : any of various naturally occurring extremely complex substances that consist of amino-acid residues joined by peptide bonds, contain the elements carbon, hydrogen, nitrogen, oxygen, usually sulfur, and occasionally other elements (such as phosphorus or iron), and include many essential biological compounds (such as enzymes, hormones, or antibodies)

2 : the total nitrogenous material in plant or animal substances

Examples of protein in a Sentence

You need more protein in your diet. These foods are an excellent source of protein. These foods have all of the essential proteins.
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Recent Examples on the Web

The other common screening option is a CA-125 blood test, which measures the amount of a protein called CA-125 in your blood. Korin Miller, SELF, "Here's Why Early Ovarian Cancer Symptoms Are So Vague," 5 Nov. 2018 Creutzfeldt–Jakob disease is a rare brain disorder caused by misfolding brain proteins called prions. Avery Thompson, Popular Mechanics, "A Man Contracted a Rare, Fatal Disease From Eating Squirrel Brains," 17 Oct. 2018 Researchers also found a link between higher pressure and one of the signs of Alzheimer’s — tangles of a protein called tau — but not another Alzheimer’s hallmark, amyloid plaques. Washington Post, "Late-life high blood pressure may harm the brain, study says," 11 July 2018 It’s also why beached whales quickly find themselves in danger: On land, a whale’s bulk damages their muscles and releases dangerous amounts of a protein called myoglobin that can cause their kidneys to fail. Brian Switek, Smithsonian, "Today’s Whales Are Huge, But Why Aren’t They Huger?," 27 June 2018 These symptoms are all triggered by consuming a protein called gluten so your gastroenterologist has likely advised you to follow a gluten-free diet. Emily Rubin, Rd, Ldn,, "Going gluten free? Dietitian shares unexpected sources of gluten," 11 June 2018 To get the right consistency, the researchers added a jelly-like goo called alginate and stem cells extracted from donor corneas, along with some ropy proteins called collagen. Rachel Becker, The Verge, "Scientists have 3D printed the most advanced artificial cornea ever using human cells," 30 May 2018 In the abdomens of male drosophila lie brain cells which produce a pleasure protein called neuropeptide corazonin, which triggers the release of sperm and seminal fluid. Melissa Healy,, "Fruit flies help explain why a male orgasm matters," 19 Apr. 2018 After a few days of having their corazonin neurons repeatedly stimulated, the flies appeared to have high levels of a protein called neuropeptide F, which spikes during rewarding situations, like eating sugar. National Geographic, "Fruit Flies Likely Enjoy Sex, Offering Clues Into Drug Addiction," 19 Apr. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'protein.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of protein

1886, in the meaning defined at sense 1

History and Etymology for protein

French protéine, from Late Greek prōteios primary, from Greek prōtos first — more at proto-

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Statistics for protein

Last Updated

13 Nov 2018

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Time Traveler for protein

The first known use of protein was in 1886

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English Language Learners Definition of protein

: a substance found in foods (such as meat, milk, eggs, and beans) that is an important part of the human diet


pro·​tein | \ˈprō-ˌtēn \

Kids Definition of protein

: a nutrient found in food (as meat, milk, eggs, and beans) that is made up of many amino acids joined together, is a necessary part of the diet, and is essential for normal cell structure and function


noun, often attributive
pro·​tein | \ˈprō-ˌtēn, ˈprōt-ē-ən \

Medical Definition of protein 

1 : any of numerous naturally occurring extremely complex substances (as an enzyme or antibody) that consist of amino acid residues joined by peptide bonds, contain the elements carbon, hydrogen, nitrogen, oxygen, usually sulfur, and occasionally other elements (as phosphorus or iron), that are essential constituents of all living cells, that are synthesized from raw materials by plants but assimilated as separate amino acids by animals, that are both acidic and basic and usually colloidal in nature although many have been crystallized, and that are hydrolyzable by acids, alkalies, proteolytic enzymes, and putrefactive bacteria to polypeptides, to simpler peptides, and ultimately to alpha-amino acids

2 : the total nitrogenous material in plant or animal substances especially : crude protein

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Comments on protein

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something that serves to warn or remind

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