each enzyme only has 1 substrate that will fit its active site. what is this called

enzymeTable of ContentsenzymeIntroduction & Top QuestionsChemical natureNomenclatureMechanism of enzyme actionFactors affecting enzyme activityFast Facts2-Min Summary Top Quest

each enzyme only has 1 substrate that will fit its active site. what is this called

enzymeTable of Contentsenzyme

  • Introduction & Top Questions
  • Chemical nature
  • Nomenclature
  • Mechanism of enzyme action
  • Factors affecting enzyme activityFast Facts
  • 2-Min Summary
  • Top Questions
  • What is an enzyme?
  • What are enzymes composed of?
  • What are examples of enzymes?
  • What factors affect enzyme activity?
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  • Article HistoryHome Health & Medicine Anatomy & Physiology

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Table of Contents

In the induced-fit theory of enzyme-substrate binding, a substrate approaches the surface of an enzyme (step 1 in box A, B, C) and causes a change in the enzyme shape that results in the correct alignment of the catalytic groups (triangles A and B; circles C and D represent substrate-binding groups on the enzyme that are essential for catalytic activity). The catalytic groups react with the substrate to form products (step 2). The products then separate from the enzyme, freeing it to repeat the sequence (step 3). Boxes D and E represent examples of molecules that are too large or too small for proper catalytic alignment. Boxes F and G demonstrate binding of an inhibitor molecule (I and I) to an allosteric site, thereby preventing interaction of the enzyme with the substrate. Box H illustrates binding of an allosteric activator (X), a nonsubstrate molecule capable of reacting with the enzyme.

enzyme See all mediaKey People:Richard Henderson Emil Fischer Maud Leonora Menten Günter Blobel Arieh Warshel...(Show more)Related Topics:neuraminidase renin-angiotensin system allosteric control induction cooperativity...(Show more)See all related content Top Questions

What is an enzyme?

  • An enzyme is a substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process.
  • The biological processes that occur within all living organisms are chemical reactions, and most are regulated by enzymes.
  • Without enzymes, many of these reactions would not take place at a perceptible rate.
  • Enzymes catalyze all aspects of cell metabolism. This includes the digestion of food, in which large nutrient molecules (such as proteins, carbohydrates, and fats) are broken down into smaller molecules; the conservation and transformation of chemical energy; and the construction of cellular macromolecules from smaller precursors.
  • Many inherited human diseases, such as albinism and phenylketonuria, result from a deficiency of a particular enzyme.phenylketonuriaRead more about phenylketonuria, an inability to metabolize phenylalanine.

What are enzymes composed of?

  • A large protein enzyme molecule is composed of one or more amino acid chains called polypeptide chains. The amino acid sequence determines the characteristic folding patterns of the proteins structure, which is essential to enzyme specificity.
  • If the enzyme is subjected to changes, such as fluctuations in temperature or pH, the protein structure may lose its integrity (denature) and its enzymatic ability.
  • Bound to some enzymes is an additional chemical component called a cofactor, which is a direct participant in the catalytic event and thus is required for enzymatic activity. A cofactor may be either a coenzymean organic molecule, such as a vitaminor an inorganic metal ion. Some enzymes require both.
  • All enzymes were once thought to be proteins, but since the 1980s the catalytic ability of certain nucleic acids, called ribozymes (or catalytic RNAs), has been demonstrated, refuting this axiom.Read more below: Chemical naturecoenzymeRead more about coenzymes.

What are examples of enzymes?

  • Practically all of the numerous and complex biochemical reactions that take place in animals, plants, and microorganisms are regulated by enzymes, and so there are many examples. Among some of the better-known enzymes are the digestive enzymes of animals. The enzyme pepsin, for example, is a critical component of gastric juices, helping to break down food particles in the stomach. Likewise, the enzyme amylase, which is present in saliva, converts starch into sugar, helping to initiate digestion.
  • In medicine, the enzyme thrombin is used to promote wound healing. Other enzymes are used to diagnose certain diseases. The enzyme lysozyme, which destroys cell walls, is used to kill bacteria.
  • The enzyme catalase brings about the reaction by which hydrogen peroxide is decomposed to water and oxygen. Catalase protects cellular organelles and tissues from damage by peroxide, which is continuously produced by metabolic reactions.catalaseRead more about catalase.

What factors affect enzyme activity?

  • Enzyme activity is affected by various factors, including substrate concentration and the presence of inhibiting molecules.
  • The rate of an enzymatic reaction increases with increased substrate concentration, reaching maximum velocity when all active sites of the enzyme molecules are engaged. Thus, enzymatic reaction rate is determined by the speed at which the active sites convert substrate to product.
  • Inhibition of enzyme activity occurs in different ways. Competitive inhibition occurs when molecules similar to the substrate molecules bind to the active site and prevent binding of the actual substrate.
  • Noncompetitive inhibition occurs when an inhibitor binds to the enzyme at a location other than the active site.
  • Another factor affecting enzyme activity is allosteric control, which can involve stimulation of enzyme action as well as inhibition. Allosteric stimulation and inhibition allow production of energy and materials by the cell when they are needed and inhibit production when the supply is adequate.Read more below: Factors affecting enzyme activityallosteric controlRead more about allosteric control.Summary

Read a brief summary of this topic

enzyme, a substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process.

A brief treatment of enzymes follows. For full treatment, see protein: Enzymes.

The biological processes that occur within all living organisms are chemical reactions, and most are regulated by enzymes. Without enzymes, many of these reactions would not take place at a perceptible rate. Enzymes catalyze all aspects of cell metabolism. This includes the digestion of food, in which large nutrient molecules (such as proteins, carbohydrates, and fats) are broken down into smaller molecules; the conservation and transformation of chemical energy; and the construction of cellular macromolecules from smaller precursors. Many inherited human diseases, such as albinism and phenylketonuria, result from a deficiency of a particular enzyme.

enzyme; cheese making

enzyme; cheese making

Enzymes also have valuable industrial and medical applications. The fermenting of wine, leavening of bread, curdling of cheese, and brewing of beer have been practiced from earliest times, but not until the 19th century were these reactions understood to be the result of the catalytic activity of enzymes. Since then, enzymes have assumed an increasing importance in industrial processes that involve organic chemical reactions. The uses of enzymes in medicine include killing disease-causing microorganisms, promoting wound healing, and diagnosing certain diseases.

Chemical nature

All enzymes were once thought to be proteins, but since the 1980s the catalytic ability of certain nucleic acids, called ribozymes (or catalytic RNAs), has been demonstrated, refuting this axiom. Because so little is yet known about the enzymatic functioning of RNA, this discussion will focus primarily on protein enzymes.

A large protein enzyme molecule is composed of one or more amino acid chains called polypeptide chains. The amino acid sequence determines the characteristic folding patterns of the proteins structure, which is essential to enzyme specificity. If the enzyme is subjected to changes, such as fluctuations in temperature or pH, the protein structure may lose its integrity (denature) and its enzymatic ability. Denaturation is sometimes, but not always, reversible.Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now

Bound to some enzymes is an additional chemical component called a cofactor, which is a direct participant in the catalytic event and thus is required for enzymatic activity. A cofactor may be either a coenzymean organic molecule, such as a vitaminor an inorganic metal ion; some enzymes require both. A cofactor may be either tightly or loosely bound to the enzyme. If tightly connected, the cofactor is referred to as a prosthetic group.

Nomenclature

An enzyme will interact with only one type of substance or group of substances, called the substrate, to catalyze a certain kind of reaction. Because of this specificity, enzymes often have been named by adding the suffix -ase to the substrates name (as in urease, which catalyzes the breakdown of urea). Not all enzymes have been named in this manner, however, and to ease the confusion surrounding enzyme nomenclature, a classification system has been developed based on the type of reaction the enzyme catalyzes. There are six principal categories and their reactions: (1) oxidoreductases, which are involved in electron transfer; (2) transferases, which transfer a chemical group from one substance to another; (3) hydrolases, which cleave the substrate by uptake of a water molecule (hydrolysis); (4) lyases, which form double bonds by adding or removing a chemical group; (5) isomerases, which transfer a group within a molecule to form an isomer; and (6) ligases, or synthetases, which couple the formation of various chemical bonds to the breakdown of a pyrophosphate bond in adenosine triphosphate or a similar nucleotide.

Mechanism of enzyme action

In most chemical reactions, an energy barrier exists that must be overcome for the reaction to occur. This barrier prevents complex molecules such as proteins and nucleic acids from spontaneously degrading, and so is necessary for the preservation of life. When metabolic changes are required in a cell, however, certain of these complex molecules must be broken down, and this energy barrier must be surmounted. Heat could provide the additional needed energy (called activation energy), but the rise in temperature would kill the cell. The alternative is to lower the activation energy level through the use of a catalyst. This is the role that enzymes play. They react with the substrate to form an intermediate complexa transition statethat requires less energy for the reaction to proceed. The unstable intermediate compound quickly breaks down to form reaction products, and the unchanged enzyme is free to react with other substrate molecules.

enzyme; active site

enzyme; active site

Only a certain region of the enzyme, called the active site, binds to the substrate. The active site is a groove or pocket formed by the folding pattern of the protein. This three-dimensional structure, together with the chemical and electrical properties of the amino acids and cofactors within the active site, permits only a particular substrate to bind to the site, thus determining the enzymes specificity.

Enzyme synthesis and activity also are influenced by genetic control and distribution in a cell. Some enzymes are not produced by certain cells, and others are formed only when required. Enzymes are not always found uniformly within a cell; often they are compartmentalized in the nucleus, on the cell membrane, or in subcellular structures. The rates of enzyme synthesis and activity are further influenced by hormones, neurosecretions, and other chemicals that affect the cells internal environment.

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