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

As enzimas são catalisadores biológicos que aceleram a taxa de reações bioquímicas. A maioria das enzimas são proteínas, compostas por aminoácidos;enquanto algumas são moléculas de RNA conhecidas como ribozimas. As enzimas atuam na dedução da energia de ativação de uma reação, aumentando a taxa de reação.Podem catalisar ambas as sínteses e quebra de ligações químicas mas não afetam a direção ou o equilíbrio da reação. Cada enzima liga-se a um reagente específico, chamado de substrato, e catalisa uma reação em particular. O substrato liga-se a uma região catalítica distinta da enzima chamada a zona ativa através de interações tais como forças intermoleculares e ligações covalentes transitórias, que resultam num complexo enzima-substrato.Esta ligação é altamente específica devido à complementaridade e conformidade necessária entre a enzima e o seu substrato. Assim, uma enzima em particular só pode catalisar reações específicas com base na sua conformação. Uma forma simples de entender a formação complexa é o modelo chave-fechadura, que levanta a hipótese de que o substrato encaixa na zona ativa da enzima, correspondente a um encaixe chave na sua fechadura"No entanto, outro modelo, o modelo de ajuste induzido, tem em conta a natureza dinâmica do complexo.Este modelo afirma que quando um substrato se liga, induz pequenas alterações conformacionais, resultando num melhor encaixe que favorece a reação. A energia de ativação para uma reação pode ser diminuída por vários métodos. Os mecanismos comuns incluem a indução de mudanças conformacionais no substrato que permite que uma ligação seja quebrada mais facilmente ou ter os grupos reativos de dois substratos bastante próximos, promovendo assim a formação de ligações.A atividade enzimática pode ser temporária ou permanentemente suprimida por moléculas naturais ou sintéticas chamadas de inibidores. Por exemplo, um inibidor competitivo compete com o substrato para se ligar à enzima da zona ativa, evitando assim a ligação do substrato. Por outro lado, um inibidor não competitivo liga-se a outro local na enzima, o que causa uma mudança conformacional na zona ativa, reduzindo a atividade catalítica das enzimas

enzimas

Dentro dos organismos vivos, as enzimas funcionam como catalisadores para muitas reações bioquímicas envolvidas no metabolismo celular. O papel das enzimas é reduzir as energias de ativação das reações bioquímicas através da formação de complexos com os seus substratos. A redução das energias de ativação favorece um aumento nas velocidades das reações bioquímicas.
As deficiências enzimáticas podem frequentemente traduzir-se em doenças que causam risco de vida. Por exemplo, uma anormalidade genética que resulta na deficiência da enzima G6PD (glicose-6-fosfato desidrogenase) afeta adversamente a via metabólica que fornece NADPH às células.
Uma interrupção nesta via metabólica pode reduzir a glutationa em glóbulos vermelhos causando danos em outras enzimas e proteínas como a hemoglobina. A metabolização excessiva da hemoglobina aumenta o nível de bilirrubina, o que leva à icterícia, condição que se pode tornar grave. Por isso, os povos que sofrem de deficiência em G6PD devem evitar determinados alimentos e medicamentos que contêm produtos químicos que poderiam provocar danos nos seus glóbulos vermelhos deficientes em glutationa. 
Função e Estrutura Enzimática
As enzimas estão agrupadas em classes diferentes com base na função específica que desempenham. Por exemplo, oxidoredutases estão envolvidas em reações redox, enquanto que transferases catalisam a transferência de grupos funcionais. A formação de ligações com hidrólise de ATP requer ligases, enquanto que as reações de hidrólise e a formação de ligações duplas são catalisadas por hidrolases e liases, respectivamente. As enzimas isomerase normalmente catalisam reações de isomerização.
As enzimas geralmente possuem locais ativos. Estas são regiões específicas da molécula com uma conformação que favorece a ligação da enzima a um substrato específico (uma molécula de reagente) para formar um complexo enzima-substrato ou o intermediário da reação.
Dois modelos—o modelo de cadeado e chave e o modelo de adaptação induzida—tentam explicar o funcionamento de um local ativo (Figura 1). A hipótese mais simplista de cadeado e chave sugere que o local ativo e a forma molecular do substrato são complementares—encaixando-se um no outro como uma chave em um cadeado (Figura 1a). Por outro lado, a hipótese de adaptação induzida sugere que a molécula enzimática é flexível e muda de forma para acomodar uma ligação com o substrato (Figura 1b).
No entanto, tanto o modelo de cadeado e chave como o modelo de adaptação induzida são responsáveis pelo facto de as enzimas só se poderem ligar a substratos específicos e catalisar apenas uma reação específica.
<img alt="Eq1" src="/files/ftp_upload/11384/11384_Image_1.png" style="text-align: center; height: 300px;" />
Figura 1 (a) De acordo com o modelo de cadeado e chave, a forma do local ativo de uma enzima é um encaixe perfeito para o substrato. (b) De acordo com o modelo de adaptação induzida, o local ativo é algo flexível, e pode mudar de forma para se ligar ao substrato.
Inibidores Enzimáticos
A atividade das enzimas também pode ser interrompida pelo processo de inibição enzimática. Existem vários tipos comuns de inibição enzimática.
Durante a inibição competitiva, uma molécula (natural ou sintética) que não o substrato liga-se diretamente ao local ativo da enzima. A semelhança estrutural e química do inibidor com o substrato facilita a sua ligação ao local ativo. Tais inibidores competitivos competem, assim, com substratos, impedindo-os de se ligarem à enzima. Frequentemente, o aumento da concentração do substrato pode suprimir os efeitos da inibição competitiva.
Na inibição não competitiva, uma molécula (natural ou sintética) liga-se a uma região alósterica (outra) da enzima, diferente do seu local ativo. A ligação do inibidor provoca uma alteração conformacional no local ativo da enzima, resultando em uma diminuição da capacidade da enzima catalisar a reação. Ao contrário da inibição competitiva, o aumento da concentração do substrato não atenua os efeitos inibitórios da inibição não competitiva.
Parte deste texto é adaptado de <a href="https://openstax.org/books/chemistry-2e/pages/12-7-catalysis">Openstax, Chemistry 2e, Section 12.7: Catalysis.</a>

Enzimas

Dentro dos organismos vivos, as enzimas atuam como catalisadores para muitas reações bioquímicas envolvidas no metabolismo celular. O papel das enzimas é reduzir o ...

Education

JoVE Core

Química

Chemical Kinetics

Cinética Química

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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

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 - Química dá vida a conceitos gerais de química usando vídeos de animação fáceis de entender. Além disso, nos vídeos Cientistas em ação, demonstramos experimentos de pesquisa clássicos e originais realizados atualmente por cientistas em laboratórios em todo o mundo.

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.2.1

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Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

PS.Chm.2.2

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	...

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PS.Chm.3.1

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PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Enzyme Action and Inhibition

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