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

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.5.1

Enzymes

Enzymes are biological catalysts that accelerate the rate of biochemical reactions. Most enzymes are proteins, made up of amino acids; while some are RNA molecules known as ribozymes. 
Enzymes act by lowering the activation energy of a reaction, thereby increasing the reaction rate. They can catalyze both synthesis and breakdown of chemical bonds, but do not affect the direction or equilibrium of the reaction. 
Each enzyme binds to a specific reactant, called the substrate, and catalyzes a particular reaction. The substrate binds to a distinct catalytic region of the enzyme called the active site through interactions such as intermolecular forces and transient covalent bonds, resulting in an enzyme-substrate complex.
This binding is highly specific due to the conformational complementarity required between the enzyme and its substrate. Thus, a particular enzyme can only catalyze specific reactions based on its conformation. 
A simple way of understanding complex formation is the lock-and-key model, which hypothesizes that the substrate fits into the enzyme&#39;s active site, analogous to a &#39;key&#39; fitting into its corresponding &#39;lock&#39;. 
However, another model, the induced-fit model, takes into account the dynamic nature of the complex. This model states that when a substrate binds, it induces small conformational changes, resulting in a tighter fit that favors the reaction. 
The activation energy for a reaction can be lowered by various methods. 
Common mechanisms include inducing conformational changes in the substrate that allow a bond to be broken more easily or bringing the reactive groups of two substrates in close proximity, thereby promoting bond formation.\Enzyme activity can be temporarily or permanently suppressed by natural or synthetic molecules called inhibitors.
For example, a competitive inhibitor competes with the substrate to bind to the enzyme&#39;s active site, thereby preventing substrate binding.
On the other hand, a noncompetitive inhibitor binds to another location on the enzyme, which causes a conformational change at the active site, reducing the enzyme&#8217;s catalytic activity.

enzymes

Inside living organisms, enzymes act as catalysts for many biochemical reactions involved in cellular metabolism. The role of enzymes is to reduce the activation energies of biochemical reactions by forming complexes with its substrates. The lowering of activation energies favor an increase in the rates of biochemical reactions.
Enzyme deficiencies can often translate into life-threatening diseases. For example, a genetic abnormality resulting in the deficiency of the enzyme G6PD (glucose-6-phosphate dehydrogenase) adversely affects the metabolic pathway supplying NADPH to cells.
A disruption in this metabolic pathway can reduce glutathione in red blood cells causing damage to other enzymes and proteins like hemoglobin. The excessive metabolization of hemoglobin builds up the bilirubin level, which leads to jaundice, a condition that can become severe. Hence, people who suffer from G6PD deficiency must avoid certain foods and medicines containing chemicals that could trigger damage to their glutathione-deficient red blood cells.
Enzyme Function and Structure
Enzymes are grouped into different classes based on the specific function they perform. For example, oxidoreductases are involved in redox reactions, while transferases catalyze the transfer of functional groups. Bond formation with ATP hydrolysis requires ligases, whereas hydrolysis reactions and double bonds formation are catalyzed by hydrolases and lyases, respectively. Isomerase enzymes usually catalyze isomerization reactions.
Enzymes generally possess active sites. These are specific regions on the molecule with a conformation that favors the enzyme to bind to a specific substrate (a reactant molecule) to form an enzyme-substrate complex or the reaction intermediate.
Two models&#8212;the lock-and-key model and the induced-fit model&#8212;attempt to explain the working of an active site (Figure 1). The most simplistic lock-and-key hypothesis suggests that the active site and the molecular shape of the substrate are complementary&#8212;fitting together like a key in a lock (Figure 1a). On the other hand, the induced-fit hypothesis suggests that the enzyme molecule is flexible and changes shape to accommodate a bond with the substrate (Figure 1b).
However, both the lock-and-key model and the induced-fit model account for the fact that enzymes can only bind with specific substrates and catalyzes only a particular reaction.
<img alt="Enzyme-substrate interaction diagram showing catalytic process sequence." src="/files/ftp_upload/11384/11384_Image_1.png" style="text-align: center; height: 300px;" data-altupdatedat="1754904545000" data-alt="Enzyme catalysis process with substrate binding and product release, schematic diagram." />
Figure 1 (a) According to the lock-and-key model, the shape of an enzyme&#8217;s active site is a perfect fit for the substrate. (b) According to the induced fit model, the active site is somewhat flexible, and can change shape in order to bond with the substrate.
Enzyme Inhibitors
The activity of enzymes can also be interrupted by the process of enzyme inhibition. There are several common types of enzyme inhibition.
During competitive inhibition, a molecule (natural or synthetic) other than the substrate directly binds to the enzyme's active site. The structural and chemical similarity of the inhibitor to the substrate facilitates its binding to the active site. Such competitive inhibitors, thus, compete with substrates, preventing them from binding to the enzyme. Most often, increasing substrate concentration can suppress the effects of competitive inhibition.
In non-competitive inhibition, a molecule (natural or synthetic) binds to an allosteric (other) region of the enzyme, different from its active site. The inhibitor-binding causes a conformational change to the enzyme's active site, resulting in a decrease in the enzyme's ability to catalyze the reaction. Unlike competitive inhibition, an increase in substrate concentration does not mitigate the inhibitory effects of non-competitive inhibition.
Part of this text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/12-7-catalysis">Openstax, Chemistry 2e, Section 12.7: Catalysis.</a>

Inside living organisms, enzymes act as catalysts for many biochemical reactions involved in cellular metabolism. The role of enzymes is to reduce the ...

Education

JoVE Core

Chemical Kinetics

KEY TERMS AND CONCEPTS

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 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

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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Enzyme Action and Inhibition

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