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.

Definitions of protein
  1. noun
    any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes
    “a diet high in protein
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    the outer covering of protein surrounding the nucleic acid of a virus
    a protein substance that remains when starch is removed from cereal grains; gives cohesiveness to dough
    recombinant protein
    a protein derived from recombinant DNA
    a protein complex in muscle fibers; composed of myosin and actin; shortens when stimulated and causes muscle contractions
    granular protein in outermost layer of endosperm of many seeds or cereal grains
    (pathology) a waxy translucent complex protein resembling starch that results from degeneration of tissue
    a protein that combines with a coenzyme to form an active enzyme
    compound protein, conjugated protein
    a protein complex combining amino acids with other substances
    any of several complex proteins that are produced by cells and act as catalysts in specific biochemical reactions
    a white insoluble fibrous protein formed by the action of thrombin on fibrinogen when blood clots; it forms a network that traps red cells and platelets
    the main protein of the keratohyalin granules
    growth factor
    a protein that is involved in cell differentiation and growth
    a protein in plasma that binds free hemoglobin and removes it (as from wounds)
    iodinated protein, iodoprotein
    a protein that contains iodine
    any of several substances found in the nuclei of all living cells; consists of a protein bound to a nucleic acid
    retinal protein formed by the action of light on rhodopsin
    containing chemically bound phosphoric acid
    plasma protein
    any of the proteins in blood plasma
    PSA, prostate specific antigen
    a protein manufactured exclusively by the prostate gland; PSA is produced for the ejaculate where it liquifies the semen and allows sperm cells to swim freely; elevated levels of PSA in blood serum are associated with benign prostatic hyperplasia and prostate cancer
    the full complement of proteins produced by a particular genome
    simple protein
    a protein that yields only amino acids when hydrolyzed
    any of various protein molecules secreted by cells of the immune system that serve to regulate the immune system
    a protein containing 20% iron that is found in the intestines and liver and spleen; it is one of the chief forms in which iron is stored in the body
    any of a large variety of proteins normally present in the body or produced in response to an antigen which it neutralizes, thus producing an immune response
    corn gluten
    gluten prepared from corn
    wheat gluten
    gluten prepared from wheat
    ADA, adenosine deaminase
    an enzyme found in mammals that can catalyze the deamination of adenosine into inosine and ammonia
    one of the proteins into which actomyosin can be split; can exist in either a globular or a fibrous form
    albumen, albumin
    a simple water-soluble protein found in many animal tissues and liquids
    NGF, nerve growth factor
    a protein that is involved in the growth of peripheral nerve cells
    a milk protein used in making e.g. plastics and adhesives
    any of a group of proteins found in saliva and pancreatic juice and parts of plants; help convert starch to sugar
    an enzyme that hydrolyses acetylcholine (into choline and acetic acid)
    an enzyme that induces coagulation
    any enzyme that catalyzes the hydrolysis of collagen and gelatin
    one of a series of enzymes in the blood serum that are part of the immune response
    TNF, tumor necrosis factor, tumour necrosis factor
    a proinflammatory cytokine that is produced by white blood cells (monocytes and macrophages); has an antineoplastic effect but causes inflammation (as in rheumatoid arthritis)
    enzyme found in most plant and animal cells that functions as an oxidative catalyst; decomposes hydrogen peroxide into oxygen and water
    Cox, cyclooxygenase
    either of two related enzymes that control the production of prostaglandins and are blocked by aspirin
    any of the enzymes that hydrolize the carboxyl group
    an enzyme that removes the iodine radical
    an enzyme that catalyzes the hydrolysis of disaccharides into monosaccharides
    a pancreatic enzyme that catalyzes the hydrolysis of elastin
    enzyme in the intestinal juice that converts inactive trypsinogen into active trypsin
    a conjugated protein having a carbohydrate component
    haemoprotein, hemoprotein
    a conjugated protein linked to a compound of iron and porphyrin
    enzyme that acts as a catalyst in converting histidine to histamine
    Hyazyme, hyaluronidase, spreading factor
    an enzyme (trade name Hyazyme) that splits hyaluronic acid and so lowers its viscosity and increases the permeability of connective tissue and the absorption of fluids
    a preparation made from iodinated protein and having an action similar to thyroxine
    an iodine containing protein that is obtained from the thyroid gland and exhibits the general properties of the globulins
    an enzyme that catalyzes its substrate to an isomeric form
    an enzyme that catalyzes the conversion of a proenzyme to an active enzyme
    an enzyme secreted in the digestive tract that catalyzes the breakdown of fats into individual fatty acids that can be absorbed into the bloodstream
    a conjugated protein having a lipid component; the principal means for transporting lipids in the blood
    a cytokine secreted by helper T cells in response to stimulation by antigens and that acts on other cells of the immune system (as by activating macrophages)
    lysozyme, muramidase
    an enzyme found in saliva and sweat and tears that destroys the cell walls of certain bacteria
    MAO, monoamine oxidase
    an enzyme that catalyzes the oxidation of many body compounds (e.g., epinephrine and norepinephrine and serotonin)
    an enzyme of nitrogen-fixing microorganisms that catalyzes the conversion of nitrogen to ammonia
    general term for enzymes that catalyze the hydrolysis of nucleic acid by cleaving chains of nucleotides into smaller units
    any of the enzymes that catalyze biological oxidation
    an enzyme that catalyzes oxidation-reduction
    a proteolytic enzyme obtained from the unripe papaya; used as a meat tenderizer
    beta-lactamase, penicillinase
    enzyme produced by certain bacteria that inactivates penicillin and results in resistance to that antibiotic
    an enzyme produced in the stomach that splits proteins into peptones
    precursor of pepsin; stored in the stomach walls and converted to pepsin by hydrochloric acid in the stomach
    any of a group of enzymes that act as a catalyst in the hydrolysis of organic phosphates
    fibrinolysin, plasmin
    an enzyme that dissolves the fibrin of blood clots
    an enzyme that catalyzes the formation of new DNA and RNA from an existing strand of DNA or RNA
    peptidase, protease, proteinase, proteolytic enzyme
    any enzyme that catalyzes the splitting of proteins into smaller peptide fractions and amino acids by a process known as proteolysis
    an enzyme that catalyses the biochemical reduction of some specified substance
    chymosin, rennin
    an enzyme that occurs in gastric juice; causes milk to coagulate
    a set of enzymes believed to snip pieces off a longer protein producing fragments of amyloid protein that bunch up and create amyloid protein plaques in brain tissue (the pathological hallmark of Alzheimer's)
    a family of proteins found in blood and milk and muscle and in plant seed
    gamma globulin, human gamma globulin
    a plasma protein containing the immunoglobulins that are responsible for immune responses
    clotting factor, coagulation factor
    any of the factors in the blood whose actions are essential for blood coagulation
    globin, haematohiston, hematohiston
    a colorless protein obtained by removing heme from hemoglobin; the oxygen carrying compound in red blood cells
    a simple protein found in the seeds of cereals
    a simple protein containing mainly basic amino acids; present in cell nuclei in association with nucleic acids
    a simple protein found in plants
    a simple protein found in fish sperm; rich in arginine; simpler in composition than globulin or albumin; counteracts the anticoagulant effect of heparin
    albuminoid, scleroprotein
    a simple protein found in horny and cartilaginous tissues and in the lens of the eye
    an antibody acting against tissues of the organism that produces it
    an antibody that causes precipitation when it unites with its antigen
    ABO antibodies
    blood type antibodies
    Rh antibody
    rhesus factor antibody
    an antibody that can neutralize a specific toxin
    an antibody that causes agglutination of a specific antigen
    Forssman antibody, heterophil antibody, heterophile antibody
    an antibody found in the blood of someone suffering from infectious mononucleosis
    alloantibody, isoantibody
    an antibody that occurs naturally against foreign tissues from a person of the same species
    monoclonal, monoclonal antibody
    any of a class of antibodies produced in the laboratory by a single clone of cells or a cell line and consisting of identical antibody molecules
    an antibody in blood serum that attaches to invading microorganisms and other antigens to make them more susceptible to the action of phagocytes
    Ig, immune gamma globulin, immune globulin, immune serum globulin, immunoglobulin
    a class of proteins produced in lymph tissue in vertebrates and that function as antibodies in the immune response
    an enzyme produced by some hemolytic strains of streptococcus that dissolves fibrinous secretions from infections; used medicinally (often in combination with streptokinase)
    an enzyme produced by some strains of streptococcus that can liquefy blood clots by converting plasminogen to plasmin; used medicinally in some cases of myocardial infarction and pulmonary embolism
    SOD, superoxide dismutase
    an enzyme that catalyzes the conversion of superoxide into hydrogen peroxide and oxygen
    an enzyme in eukaryotic cells that can add telomeres to the ends of chromosomes after they divide
    any of various enzymes that move a chemical group from one compound to another compound
    an enzyme of pancreatic origin; catalyzes the hydrolysis of proteins to smaller polypeptide units
    an enzyme that catalyzes the hydrolysis of urea into carbon dioxide and ammonia; is present in intestinal bacteria
    a complex of enzymes that cause glycolysis; originally found in yeast but also present in higher organisms
    type of:
    macromolecule, supermolecule
    any very large complex molecule; found only in plants and animals
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