Name: how catalysts lower reaction barriers
Uploaded: 2019-03-11T09:21:09.000Z
Duration: 1 min 26 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Chemistry

Matter And Its Interactions

HS-PS1-4

Activation Energy

- [Narratore] L'energia
di attivazione è l'energia

necessaria per avviare
una reazione chimica

tra i reagenti che sono presenti.

La fonte viene spesso
fornita dall'energia termica,

che fa muovere le molecole più velocemente

e le fa scontrare l'una contro l'altra,

causando la rottura dei
legami dei reagenti.

Quindi, i reagenti originali
richiedevano energia libera

perché la reazione si verifichi,

rappresentata come la parte
in salita di questa curva,

ed è la quantità di energia di
attivazione per la reazione.

Al culmine, noto come
stato di transizione,

le molecole non legate sono
ora in condizioni instabili.

Come gli atomi si
ricollegano con nuovi legami,

rilasciano energia libera nell'ambiente,

che viene mostrato come la
parte in discesa della reazione.

Gli umani metabolizzano
zucchero e grasso per l'energia;

se l'energia termica fosse
usata per abbattere le molecole,

così tanta energia libera
sarebbe rilasciata come calore,

che le proteine nella
cellula avrebbero denaturato.

Invece, sostanze conosciute
come catalizzatori

sono specificatamente aggiunte
per regolare la velocità

del metabolismo, come accelerarlo.

Ad esempio, un catalizzatore
biologico, un enzima, abbassa

l'energia di attivazione
richiesta per rompere i legami

e consente alle reazioni di
verificarsi a tassi ragionevoli

senza danni cellulari.

Robinson, Peter K. "Enzimi: principi e applicazioni biotecnologiche". Saggi in biochimica 59 (15 novembre 2015): 1–41. [<a href="https://doi.org/10.1042/bse0590001" target="__blank">Sorgente</a>]

energia di attivazione

L'energia di attivazione è la quantità minima di energia necessaria affinché una reazione chimica proceda in avanti. Più alta è l'energia di attivazione, più lento è il tasso della reazione. Tuttavia, l'aggiunta di calore alla reazione aumenterà il tasso, poiché provoca che le molecole si muovano più velocemente e aumentino la probabilità che le molecole collidano. La collisione e la rottura dei legami rappresenta la fase in salita di una reazione e genera lo stato di transizione. Lo stato di transizione è uno stato instabile ad alta energia dei reanti. La formazione di nuovi legami chimici e prodotti finali, e il rilascio di energia libera è la fase in discesa della reazione. I catalizzatori aumentano il tasso di reazione abbassando l'energia di attivazione. Ad esempio, in biologia, gli enzimi che metabolizzano lo zucchero e i grassi aumentano il tasso con cui avviene la loro ripartizione e allo stesso tempo impediscono la sovrapproduzione di energia libera che altrimenti denaturano le proteine nella cellula.

<h4>Catalizzatori</h4>

Un catalizzatore è una sostanza che aumenta il tasso di reazione abbassando l'energia di attivazione e, nel processo, si rigenera. Un catalizzatore fornisce un percorso alternativo o un meccanismo per la reazione che avviene e accelera sia le reazioni in avanti che inverse. In biologia, gli enzimi sono esempi di catalizzatori perché abbassano l'energia di attivazione necessaria per le reazioni nel metabolismo cellulare.

Per esempio, gli esseri umani metabolizzano lo zucchero e i grassi per l'energia. Gli enzimi sono vitali per l'uomo per abbattere queste molecole, perché se si utilizzasse l'energia termica da sola, l'energia libera rilasciata sotto forma di calore causerebbe la denaturazione delle proteine nella cellula. Inoltre, l'energia termica catalizzare in modo non specifico tutte le reazioni. Tuttavia, gli enzimi si legano solo a specifici reati chimici, chiamati substrati, e abbassano la loro energia di attivazione per catalizzare le reazioni cellulari selettive.

Energia di attivazione

Activation energy is the minimum amount of energy necessary for a chemical reaction to move forward. The higher the activation energy, the slower the rate ...

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JoVE Core

Biology

Biologia

Cellular Processes

Processi cellulari

Metabolism

Metabolismo

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

how catalysts lower reaction barriers

Activation energy is the minimum energy a chemical reaction needs to keep going. When the activation energy is higher, the reaction usually happens more slowly. Adding heat can speed the reaction because molecules move faster and collide more often.

As reactants collide, bonds break and the reaction moves through an uphill phase. That step creates the transition state, which is an unstable, high-energy state of the reactants. After that, new bonds form, products appear, and free energy is released in the downhill phase.

Catalysts speed up reactions by lowering the activation energy. A catalyst is a substance that takes part in the reaction pathway and then regenerates itself. It offers an alternate mechanism and speeds up both the forward and reverse reactions.

In biology, enzymes are catalysts that help cells control metabolism. They help break down sugar and fat for energy, and they do it without releasing too much free energy as heat. That matters because excess heat could denature proteins in the cell.

Enzymes are also selective. They bind only to specific reactants called substrates and lower the activation energy for those reactions. Thermal energy alone would not be as selective and could drive many reactions at once, but enzymes support specific cellular reactions instead.

How Catalysts Lower Reaction Barriers

what is metabolism?

Metabolism, Energy, and Cell Reactions

Metabolism is the set of chemical reactions that happen in a cell. It includes anabolism, which builds molecules, and catabolism, which breaks them down. These reactions help cells manage energy and keep life processes running. Cells use metabolism to turn food into energy, make cell parts, and remove waste products. Food stores potential energy in the bonds between atoms. Catabolic pathways break large food molecules into smaller ones and release that energy. Anabolic pathways use that energy...

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Entropy in Food Web Energy Flow

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kinetic energy

Motion as a Source of Energy

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potential energy

Stored Energy in Motion and Bonds

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free energy

Gibbs Free Energy in Chemical Reactions

Gibbs free energy is a measure of useful energy that can be taken from a chemical reaction to do work. It is written as G and named for scientist Gibbs, who discovered it. This energy is what remains after entropy is considered. A reaction can either take in energy or release it. Reactions that absorb energy are called endergonic reactions. Reactions that release energy are called exergonic reactions. The direction of energy flow helps show which type of reaction is happening. Plants carry...

activation energy

Activation energy is the minimum energy a chemical reaction needs to keep going. When the activation energy is higher, the reaction usually happens more slowly. Adding heat can speed the reaction because molecules move faster and collide more often. As reactants collide, bonds break and the reaction moves through an uphill phase. That step creates the transition state, which is an unstable, high-energy state of the reactants. After that, new bonds form, products appear, and free energy is...

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ATP Breakdown and Energy Release

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phosphorylation

Phosphorylation and Protein Control

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induced-fit model

How Enzymes Adjust to Their Substrates

Enzymes speed up many chemical reactions in cells. They are biological catalysts, so they increase reaction speed without being consumed or permanently changed. They do this by lowering the activation energy needed to turn reactants into products. Enzymes are proteins that usually work by binding to a substrate, which is the reactant molecule they act on. They show substrate specificity, meaning they bind only certain substrates. This specificity depends mainly on the shape and chemical...

enzyme kinetics

Substrate Effects on Enzyme Rates

Enzyme kinetics examines how enzymes change the rate of a reaction. Enzymes speed reactions by lowering the activation energy of the reactants. The reaction rate is the speed at which an enzyme turns reactants into products, and it can be affected by several factors, including the number of available reactants. Scientists often study enzyme kinetics in a test tube with a fixed amount of enzyme. When more substrate, or reactant, is added, the reaction rate increases because the enzyme can make...

enzyme inhibition

Competitive vs Noncompetitive Inhibitors

Enzyme inhibitors are molecules that reduce enzyme activity by binding to enzymes. Cells use these inhibitors to help regulate normal enzyme function. Drugs and toxins can also block enzymes and change how they work. Some inhibitors bind at the active site, which is the part of the enzyme where the substrate normally fits. Competitive inhibitors do this by occupying the active site and preventing the substrate from binding. If the substrate concentration becomes high enough, it can outcompete...

feedback inhibition

How Cells Control Product Buildup

Cells use enzymes to run biochemical reactions and make the products they need. These reactions are happening constantly, and enzymes speed them up so they happen fast enough to matter. Enzyme activity also has to be regulated. Cells need the right amounts of starting materials, intermediate metabolites, and final products. If these substances build up too much or drop too low, the cell can be harmed. That is why cells use control systems to keep metabolic levels balanced. One important...

allosteric regulation

Allosteric Control of Enzyme Speed

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cofactors and coenzymes

Enzyme Helpers: Metals, Vitamins, and More

Enzyme helpers are needed for many enzymes to work properly. These helpers fall into two groups: cofactors and coenzymes. Cofactors are metallic ions, while coenzymes are non-protein organic molecules. Both can be tightly bound to an enzyme or attach only when the substrate binds. Cofactors are common in mature proteins, appearing in about 30% of them. They are often added as the enzyme folds and help with catalytic activity. Magnesium is one important cofactor, and it is needed by more than...

key terms and concepts

Learn how heat, transition states, catalysts, and enzymes affect reaction speed. See how lowering activation energy helps cells break down sugar and fat.

How Catalysts Lower Reaction Barriers | JoVE K12

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Tennessee Academic Standards

Energy

CHEM1.PS3.3

Minnesota Academic Standards in Science

9-12

3.1.1 9C.2.2.1.1

Alabama Course of Study Science

Physical Science

9-12.PS.1.1

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How Catalysts Lower Reaction Barriers

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