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

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.5.1

Enzymes

Enzymy są katalizatorami biologicznymi, które przyspieszają tempo reakcji biochemicznych. Większość enzymów to białka, składające się z aminokwasów; podczas gdy niektóre są cząsteczkami RNA znanymi jako rybozymy. 
Enzymy działają poprzez obniżenie energii aktywacji reakcji, zwiększając w ten sposób szybkość reakcji. Mogą katalizować zarówno syntezę, jak i rozpad wiązań chemicznych, ale nie wpływają na kierunek ani równowagę reakcji. 
Każdy enzym wiąże się z określonym reagentem, zwanym substratem, i katalizuje określoną reakcję. Substrat wiąże się z odrębnym regionem katalitycznym enzymu zwanym miejscem aktywnym poprzez interakcje, takie jak siły międzycząsteczkowe i przejściowe wiązania kowalencyjne, w wyniku czego powstaje kompleks enzym-substrat.
To wiązanie jest wysoce specyficzne ze względu na wymaganą komplementarność konformacyjną między enzymem a jego substratem. Tak więc konkretny enzym może katalizować określone reakcje tylko w oparciu o swoją konformację. 
Prostym sposobem zrozumienia tworzenia się kompleksów jest model zamka i klucza, który zakłada, że substrat pasuje do miejsca aktywnego enzymu, analogicznie do "klucza" pasującego do odpowiadającego mu "zamka". 
Jednak inny model, model indukowanego dopasowania, uwzględnia dynamiczny charakter kompleksu. Model ten stwierdza, że gdy substrat się wiąże, indukuje niewielkie zmiany konformacyjne, co skutkuje ściślejszym dopasowaniem, które sprzyja reakcji. 
Energia aktywacji reakcji może być obniżona na różne sposoby. 
Typowe mechanizmy obejmują wywoływanie zmian konformacyjnych w podłożu, które umożliwiają łatwiejsze zerwanie wiązania lub zbliżenie reaktywnych grup dwóch substratów, sprzyjając w ten sposób tworzeniu wiązań.\Aktywność enzymu może być tymczasowo lub trwale stłumiona przez naturalne lub syntetyczne cząsteczki zwane inhibitorami.
Na przykład inhibitor kompetycyjny konkuruje z substratem, aby związać się z miejscem aktywnym enzymu, zapobiegając w ten sposób wiązaniu substratu.
Z drugiej strony, niekonkurencyjny inhibitor wiąże się z innym miejscem na enzymie, co powoduje zmianę konformacyjną w miejscu aktywnym, zmniejszając aktywność katalityczną enzymu.

enzymy

Wewnątrz żywych organizmów enzymy działają jako katalizatory wielu reakcji biochemicznych związanych z metabolizmem komórkowym. Rolą enzymów jest zmniejszanie energii aktywacji reakcji biochemicznych poprzez tworzenie kompleksów z ich substratami. Obniżenie energii aktywacji sprzyja wzrostowi szybkości reakcji biochemicznych.

Niedobory enzymów często mogą prowadzić do chorób zagrażających życiu. Na przykład nieprawidłowość genetyczna powodująca niedobór enzymu G6PD (dehydrogenazy glukozo-6-fosforanowej) niekorzystnie wpływa na szlak metaboliczny dostarczający NADPH do komórek.

Zakłócenie tego szlaku metabolicznego może spowodować redukcję glutationu w czerwonych krwinkach, powodując uszkodzenie innych enzymów i białek, takich jak hemoglobina. Nadmierny metabolizm hemoglobiny zwiększa poziom bilirubiny, co prowadzi do żółtaczki, która może mieć ciężki przebieg. Dlatego osoby cierpiące na niedobór G6PD muszą unikać niektórych pokarmów i leków zawierających substancje chemiczne, które mogą spowodować uszkodzenie czerwonych krwinek z niedoborem glutationu.

Funkcja i struktura enzymu

Enzymy dzieli się na różne klasy w zależności od pełnionej przez nie funkcji. Na przykład oksydoreduktazy biorą udział w reakcjach redoks, podczas gdy transferazy katalizują przeniesienie grup funkcyjnych. Tworzenie wiązania za pomocą hydrolizy ATP wymaga ligaz, podczas gdy reakcje hydrolizy i tworzenie wiązań podwójnych są katalizowane odpowiednio przez hydrolazy i liazy. Enzymy izomerazy zwykle katalizują reakcje izomeryzacji.

Enzymy na ogół posiadają miejsca aktywne. Są to specyficzne regiony cząsteczki o konformacji, która sprzyja wiązaniu się enzymu z określonym substratem (cząsteczką reagenta) w celu utworzenia kompleksu enzym-substrat lub produktu pośredniego reakcji.

Dwa modele – model zamka i klucza oraz model indukowanego dopasowania – mogą być pomocne w wyjaśnieniu działania miejsca aktywnego (rysunek 1). Najbardziej uproszczona hipoteza zamka i klucza sugeruje, że miejsce aktywne i kształt molekularny podłoża uzupełniają się i pasują do siebie jak klucz w zamku (rysunek 1a). Z drugiej strony hipoteza dopasowania indukowanego sugeruje, że cząsteczka enzymu jest elastyczna i zmienia kształt, aby dostosować się do wiązania z podłożem (rysunek 1b).

Zarówno model zamka i klucza, jak i model indukowanego dopasowania wyjaśniają fakt, że enzymy mogą wiązać się tylko z określonymi substratami i katalizować tylko określoną reakcję.

<img alt="Eq1" src="/files/ftp_upload/11384/11384_Image_1.png" style="text-align: center; height: 300px;" />

Rycina 1 (a) Zgodnie z modelem zamka i klucza kształt miejsca aktywnego enzymu jest idealnie dopasowany do substratu. (b) Zgodnie z modelem indukowanego dopasowania miejsce aktywne jest dość elastyczne i może zmieniać kształt, aby związać się z podłożem.

Inhibitory enzymów

Aktywność enzymów może zostać przerwana także przez proces hamowania enzymów. Istnieje kilka powszechnych typów hamowania enzymów.

Podczas hamowania konkurencyjnego cząsteczka (naturalna lub syntetyczna) inna niż substrat bezpośrednio wiąże się z miejscem aktywnym enzymu. Strukturalne i chemiczne podobieństwo inhibitora do substratu ułatwia jego wiązanie z miejscem aktywnym. Takie konkurencyjne inhibitory konkurują zatem z substratami, uniemożliwiając im wiązanie się z enzymem. Najczęściej zwiększenie stężenia substratu może stłumić skutki hamowania konkurencyjnego.

W hamowaniu niekonkurencyjnym cząsteczka (naturalna lub syntetyczna) wiąże się z allosterycznym (innym) regionem enzymu, innym niż jej miejsce aktywne. Wiązanie inhibitora powoduje zmianę konformacyjną miejsca aktywnego enzymu, co skutkuje zmniejszeniem zdolności enzymu do katalizowania reakcji. W przeciwieństwie do hamowania konkurencyjnego, wzrost stężenia substratu nie łagodzi hamujących skutków hamowania niekonkurencyjnego.

Enzymy

Wewnątrz organizmów żywych enzymy działają jako katalizatory wielu reakcji biochemicznych biorących udział w metabolizmie komórkowym. Rolą enzymów jest zmniejszenie ...

Education

JoVE Core

Chemia

Jeden

Chemical Kinetics

Kinetyka chemiczna

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

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

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measuring reaction rates

Tracking Reaction Kinetics with Light and Pressure

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concentration and rate law

Reaction Order from Concentration

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determining order of reaction

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the integrated rate law: the dependence of concentration on time

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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

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reaction mechanisms

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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

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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

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 Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

Pennsylvania State Academic Standards

Physical Science

Chemical Reactions

3.2.9-12.D

3.2.9-12.E

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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

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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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Enzyme Action and Inhibition

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