Name: enzyme action and inhibition
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 34 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.5.1

Enzymes

Les enzymes sont des catalyseurs biologiques qui accélérent le rythme des réactions biochimiques. La plupart des enzymes sont des protéines, constituées d'acides aminés;tandis que certains sont des molécules d'ARN appelées ribozymes. Les enzymes agissent en abaissant l'énergie de l'activation d'une réaction, augmentant ainsi la vitesse de réaction.Ils peuvent catalyser à la fois la synthèse et la rupture des liaisons chimiques mais n'affectent pas la direction ou l'équilibre de la réaction. Chaque enzyme se lie à un réactif spécifique, appelé substrat, et catalyse une réaction particulière. Le substrat se lie à une région catalytique distincte de l'enzyme appelée site actif par des interactions telles que les forces intermoléculaires et des liaisons covalentes transitoires, résultant dans un complexe enzyme-substrat.Cette liaison est très spécifique en raison de la complémentarité conformationnelle nécessaire entre l'enzyme et son substrat. Ainsi, une enzyme particulière ne peut catalyser des réactions spécifiques sur la base de sa conformation. Un moyen simple de comprendre la formation complexe est le modèle de verrouillage et de clé, qui suppose que le substrat s'insère dans le site actif de l'enzyme, analogue à une clé"s'insérant dans sa serrure"correspondante.Cependant, un autre modèle, le modèle d'ajustement induit, tient compte de la nature dynamique du complexe. Ce modèle indique que lorsqu'un substrat se lie, il induit de petits changements conformationnels, résultant en un ajustement qui favorise la réaction. L'énergie d'activation d'une réaction peut être réduite par diverses méthodes.Les mécanismes courants incluent l'induction de changements conformationnels dans le substrat qui permettent de rompre plus facilement une liaison ou amener les groupes réactifs de deux substrats à proximité immédiate, ce qui favorise la formation de liens. L'activité enzymatique peut être supprimé de manière temporaire ou permanente par des molécules naturelles ou synthétiques appelées inhibiteurs. Par exemple, un inhibiteur compétitif entre en concurrence avec le substrat pour se lier au site actif de l'enzyme, donc empêche la liaison du substrat.D'autre part, un inhibiteur non compétitif se lie à un autre endroit de l'enzyme, ce qui provoque un changement de conformation sur le site actif, réduisant l'activité catalytique de l'enzyme.

enzymes

À l'intérieur des organismes vivants, les enzymes agissent comme des catalyseurs pour de nombreuses réactions biochimiques impliquées dans le métabolisme cellulaire. Le rôle des enzymes est de réduire les énergies d'activation des réactions biochimiques en formant des complexes avec ses substrats. La diminution des énergies d'activation favorise une élévation des vitesses de réactions biochimiques. 
 Les carences enzymatiques peuvent souvent se traduire par des maladies potentiellement mortelles. Par exemple, une anomalie génétique entraînant une déficience de l'enzyme G6PD (glucose-6-phosphate déshydrogénase) impacte négativement la voie métabolique alimentant les cellules en NADPH. 
 Une perturbation de cette voie métabolique peut réduire le glutathion dans les globules rouges causant des dommages à d'autres enzymes et protéines comme l'hémoglobine. La métabolisation excessive de l'hémoglobine augmente le taux de bilirubine, ce qui entraîne une jaunisse, un état de santé qui peut devenir grave. Par conséquent, les personnes qui souffrent d'un déficit en G6PD doivent éviter certains aliments et médicaments contenant des produits chimiques qui pourraient déclencher des dommages à leurs globules rouges déficients en glutathion. 
 Fonction et structure des enzymes 
 Les enzymes sont regroupées en différentes classes basées sur la fonction spécifique qu'elles exécutent. Par exemple, les oxydoréductases sont impliquées dans les réactions redox, tandis que les transférases catalysent le transfert de groupes fonctionnels. La formation de liaisons avec l'hydrolyse de l'ATP nécessite des ligases, alors que les réactions d'hydrolyse et la formation de doubles liaisons sont respectivement catalysées par les hydrolases et les lyases. Les enzymes isomérases catalysent généralement les réactions d'isomérisation. 
 Les enzymes possèdent généralement des sites actifs. Il s'agit de régions précises de la molécule avec une conformation qui favorise la fixation de l'enzyme à un substrat spécifique (une molécule de réactif) pour former un complexe enzyme-substrat ou l'intermédiaire de la réaction. 
 Deux modèles, le modèle clé-serrure et l'ajustement induit, tentent d'expliquer le fonctionnement d'un site actif (figure 1). L'hypothèse clé-serrure la plus simpliste suggère que le site actif et la forme moléculaire du substrat sont complémentaires, s'ajustant ensemble comme une clé dans une serrure (figure 1a). D'autre part, l'hypothèse de l'ajustement induit suggère que l'enzyme est une molécule souple et qu'elle change de forme pour adapter une liaison avec le substrat (figure 1b). 
 Cependant, le modèle clé-serrure et le modèle d'ajustement induit tiennent compte du fait que les enzymes ne peuvent se lier qu'à des substrats spécifiques et ne catalysent qu'une réaction particulière. 
 <img alt="Eq1" src="/files/ftp_upload/11384/11384_Image_1.png" style="text-align: center; height: 300px;" />
 Figure 1 (a) Selon le modèle clé-serrure, la forme du site actif d’une enzyme est parfaitement ajustée au substrat. (b) Selon le modèle d'ajustement induit, le site actif est quelque peu flexible et peut changer de forme afin de se lier au substrat. 
 Inhibiteurs enzymatiques 
 L'activité des enzymes peut également être interrompue par le processus d'inhibition enzymatique. Il existe plusieurs types communs d'inhibition enzymatique. 
 Pendant l'inhibition compétitive, une molécule (naturelle ou synthétique) autre que le substrat se lie directement au site actif de l'enzyme. La similarité structurale et chimique entre l'inhibiteur et le substrat facilite sa fixation au site actif. De tels inhibiteurs compétitifs sont, donc, en concurrence avec les substrats, les empêchant de se lier à l'enzyme. Le plus souvent, l'augmentation de la concentration du substrat peut supprimer les effets de l'inhibition compétitive. 
 En cas d'inhibition non compétitive, une molécule (naturelle ou synthétique) se lie à une région allostérique (autre) de l'enzyme, différente de son site actif. La fixation de l'inhibiteur entraîne un changement conformationnel du site actif de l'enzyme, ce qui entraîne une diminution de la capacité de l'enzyme à catalyser la réaction. Contrairement à l'inhibition compétitive, une augmentation de la concentration du substrat n'atténue pas les effets inhibiteurs de l'inhibition non compétitive. 
 Une partie de ce texte est adaptée de<a href="https://openstax.org/books/chemistry-2e/pages/12-7-catalysis"> Openstax, Chimie 2e, Section 12.7 : Catalyse. </a>

À l’intérieur des organismes vivants, les enzymes agissent comme des catalyseurs pour de nombreuses réactions biochimiques impliquées dans le métabolisme cellulaire. Le rôle des enzymes est de réduire le ...

Education

Enseignement

JoVE Core

Chimie

Chemical Kinetics

Cinétique chimique

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

enzyme action and inhibition

Enzymes are biological catalysts that speed up many reactions in living organisms. They help control cellular metabolism by lowering the activation energy needed for biochemical reactions. When activation energy drops, reaction rates can increase.

Enzyme problems can also lead to serious disease. A genetic abnormality that causes G6PD, or glucose-6-phosphate dehydrogenase, deficiency can disrupt the pathway that supplies NADPH to cells. In red blood cells, this can reduce glutathione and damage other enzymes and proteins such as hemoglobin. As hemoglobin is broken down too much, bilirubin builds up and can cause jaundice. People with G6PD deficiency often need to avoid certain foods and medicines that may trigger damage to their red blood cells.

Enzymes are grouped by the reactions they carry out. Oxidoreductases take part in redox reactions. Transferases move functional groups from one molecule to another. Ligases form bonds and use ATP hydrolysis, while hydrolases drive hydrolysis reactions and lyases help form double bonds. Isomerases catalyze isomerization reactions.

Most enzymes have an active site, which is the region that binds a specific substrate, or reactant molecule. The enzyme and substrate form an enzyme-substrate complex, which acts as the reaction intermediate. Two models explain how this binding works. In the lock-and-key model, the active site and substrate fit together like a key in a lock. In the induced-fit model, the enzyme changes shape to fit the substrate. Both models explain enzyme specificity, meaning an enzyme usually binds only certain substrates and catalyzes only one particular reaction.

Enzyme activity can also be blocked by inhibitors. In competitive inhibition, an inhibitor that is similar to the substrate binds directly to the active site and competes with the substrate. Increasing substrate concentration can often reduce this effect. In non-competitive inhibition, the inhibitor binds to an allosteric site, which is a different region of the enzyme. This binding changes the shape of the active site and lowers enzyme activity. Unlike competitive inhibition, adding more substrate does not fix non-competitive inhibition.

Enzyme Action and Inhibition

reaction rate

Measuring Reaction Rates

Measuring reaction rates shows how fast reactants are used up or products are formed over time. The rate of reaction is the change in the amount of a reactant or product per unit time. Because of that, scientists measure how a property changes as the reaction proceeds and connect that change to reactant or product amounts. For reactions that make or use a gas, the rate can be followed by changes in volume or pressure. A rate expression is the mathematical way to write how concentration changes...

measuring reaction rates

Tracking Reaction Kinetics with Light and Pressure

Reaction kinetics can be tracked with polarimetry, spectrometry, and pressure measurements. These methods let scientists follow a reaction without disturbing the sample. They also help determine how reactant or product concentrations change over time. Polarimetry is used for optically active substances. These substances rotate the plane of polarized light, which is called optical rotation. The effect comes from molecular structure. Normal monochromatic light is unpolarized, but after it passes...

concentration and rate law

Reaction Order from Concentration

Reaction order from concentration shows how reactant amounts affect reaction rate. Rate laws, also called differential rate laws or rate equations, are mathematical expressions that connect reaction rate with the concentrations of reactants. For a generic reaction a A + b B → products, the rate law can be written using the reactant concentrations [A] and [B] and a rate constant k. In a rate law, k is the rate constant for one specific reaction at one specific temperature. The exponents m and n...

determining order of reaction

Finding Rate Law from Initial Rates

Rate laws connect the speed of a chemical reaction to the concentration of its reactants. The rate constant, k, and the reaction orders are not taken from the chemical equation. They are found experimentally by watching how the rate changes when the reactant concentrations change. One common way to do this is the method of initial rates. In this method, several trials are run with different starting concentrations. The measured rates are then compared to determine the reaction orders and,...

the integrated rate law: the dependence of concentration on time

the-integrated-rate-law-the-dependence-of-concentration-on-time

Reading Reaction Progress with Integrated Laws

Integrated rate laws connect reaction concentration to time. They help show how much reactant or product is present after a certain period. They can also help estimate how long a reaction must run to reach a given extent. A common use is finding how long radioactive material must be stored before its radioactivity drops to a safe level. These equations come from the differential rate law after it is integrated with respect to time. For a first-order reaction, where rate = k[A], the integrated...

half-life of a reaction

Reaction Half-Life in Kinetics

Reaction half-life is the time needed for half of a reactant to be consumed. After each half-life, half of the remaining reactant is used up. A hydrogen peroxide decomposition example shows this pattern clearly. The concentration drops from 1.000 M to 0.500 M in the first 6.00 hours, then to 0.250 M in the next 6.00 hours, and then to 0.125 M in the third period. Each later 6.00-hour interval removes half of what is left. For first-order reactions, the half-life does not depend on the reactant...

temperature dependence on reaction rate

Collision Theory and Reaction Speed

Collision theory explains why reaction speed depends on how particles collide. Atoms, molecules, or ions must come close together before they can react. The theory says the reaction rate depends on the collision rate, the orientation of the colliding species, and whether the collision has enough energy for bonds to change. A gas-phase reaction between carbon monoxide and oxygen shows why orientation matters. The molecules can collide in more than one way. If the oxygen side of carbon monoxide...

arrhenius plots

Determining Activation Energy from Temperature

The Arrhenius equation links activation energy and the rate constant, k, for chemical reactions. It is written as k = Ae−Ea/RT. In this equation, R is the ideal gas constant with a value of 8.314 J/mol·K, T is the temperature on the kelvin scale, Ea is the activation energy in J/mole, e is the constant 2.7183, and A is the frequency factor. The frequency factor depends on collision frequency and the orientation of reacting molecules. Experimental kinetic data can be used to find the activation...

reaction mechanisms

Elementary Steps in Reaction Mechanisms

Chemical reactions can happen in steps, and a balanced equation does not show the full path at the molecular level. A reaction mechanism, also called a reaction path, gives the step-by-step process that explains how reactants become products. The decomposition of ozone is one example of a reaction that can be described by a sequence of steps. Each step in a mechanism is an elementary reaction. These elementary reactions happen in order, and when they are added together, they give the balanced...

rate-determining steps

Reaction Bottlenecks in Chemical Kinetics

Reaction bottlenecks help explain rate-determining steps in multistep reaction mechanisms. In a mechanism with several elementary steps, one step is often much slower than the others. That slowest step is called the rate-limiting step, or rate-determining step. A reaction cannot move faster than its slowest step, so this step controls the overall reaction rate. The idea is like traffic on a four-lane freeway with one lane closed. Cars can only move as fast as the bottleneck allows. In the same...

catalysis

Catalyst Action in Reaction Rates

Catalysts change the rate of a chemical reaction by giving it a faster path. A catalyst increases reaction rate without being consumed during the process. Its effect is often explained with reaction mechanisms and energy diagrams. For an endothermic reaction, the reactants and products start and end at the same energies in both cases. The uncatalyzed path is a one-step mechanism with one transition state. The catalyzed path follows a different mechanism with two transition states and a lower...

Enzymes are biological catalysts that speed up many reactions in living organisms. They help control cellular metabolism by lowering the activation energy needed for biochemical reactions. When activation energy drops, reaction rates can increase. Enzyme problems can also lead to serious disease. A genetic abnormality that causes G6PD, or glucose-6-phosphate dehydrogenase, deficiency can disrupt the pathway that supplies NADPH to cells. In red blood cells, this can reduce glutathione and...

key terms and concepts

Explore how enzymes speed reactions, how active sites work, and how competitive and non-competitive inhibitors affect enzyme activity in high school biology.

Enzyme Action and Inhibition | JoVE K12

chemistry

JoVE Core Chimie anime les concepts de chimie générale en utilisant des leçons vidéo concises et faciles à comprendre. De plus, nos vidéos de scientifiques à l'action présentent des expériences de recherche, classiques ou insolites, effectuées dans des laboratoires modernes du monde entier.

Pennsylvania State Academic Standards

Physical Science

Chemical Reactions

3.2.9-12.D

3.2.9-12.E

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.f

Arizona Science Standards

High School

HS.P1

HS.P1U1.3

Next Generation Science Standards

Matter and Its Interactions

HS-PS1-4

HS-PS1-5

Florida Department of Education

SC.912.P.12

SC.912.P.12.12

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PS.Chm.2.2

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Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

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Construct an explanation to summarize the influences intermolecular forces have on the properties of chemical compounds.

PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Enzyme Action and Inhibition

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