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

Aktivierungsenergie ist die Energie, die benötigt wird, um eine chemische Reaktion zwischen den vorhandenen Reaktanten auszulösen.
 Die Quelle wird häufig durch Wärmeenergie gespeist, wodurch sich Moleküle schneller bewegen und miteinander kollidieren und die Bindungen der Reaktanten aufbrechen.
 Somit benötigten die ursprünglichen Reaktanten freie Energie, damit die Reaktion ablief, dargestellt als der ansteigende Teil dieser Kurve, dies ist die Menge an Aktivierungsenergie für die Reaktion.
 Auf dem Höhepunkt, der als Übergangszustand bekannt ist, befinden sich die ungebundenen Moleküle jetzt in einem instabilen Zustand.
 Wenn sich Atome mit neuen Bindungen verbinden, geben sie freie Energie an die Umgebung ab, was als abschüssiger Teil der Reaktion dargestellt wird.
 Während der Mensch Zucker und Fett zu Energie umwandelt, würde beim Abbau dieser Moleküle durch thermische Energie so viel freie Energie als Wärme freigesetzt, dass die Proteine in der Zelle denaturieren würden.
 Stattdessen werden gezielt als Katalysatoren bekannte Substanzen zugesetzt, um die Stoffwechselrate zu regulieren, beispielsweise um sie zu beschleunigen.
 Beispielsweise senkt ein biologischer Katalysator, ein Enzym, die Aktivierungsenergie, die zum Aufbrechen von Bindungen erforderlich ist und ermöglicht das Auftreten von Reaktionen mit angemessenen Raten ohne Zellschädigung.

Robinson, Peter K. "Enzyme: Prinzipien und biotechnologische Anwendungen." Essays in Biochemistry 59 (15. November 2015): 1–41. [<a href="https://doi.org/10.1042/bse0590001" target="__blank">Quelle</a>]

aktivierungsenergie

Die Aktivierungsenergie stellt die minimale Energiemenge dar, welche für den Ablauf einer chemischen Reaktion benötigt wird. Je höher die Aktivierungsenergie, desto langsamer ist die Reaktionsgeschwindigkeit. Durch die Zufuhr von Wärme zur Reaktion wird die Geschwindigkeit erhöht, da sich die Moleküle nun schneller bewegen und somit die Wahrscheinlichkeit steigt, dass die Moleküle miteinander kollidieren. Die Kollisionen und das Aufbrechen von Bindungen stellt die Anstiegsphase einer Reaktion dar und erzeugt den Übergangszustand. Der Übergangszustand ist ein instabiler hochenergetischer Zustand der Edukte. Die Bildung neuer chemischer Bindungen und der Endprodukte sowie die Freisetzung freier Energie ist die abfallende Reaktionsphase. Katalysatoren erhöhen die Geschwindigkeit einer Reaktion, indem sie die Aktivierungsenergie senken. Zum Beispiel erhöhen Enzyme die Geschwindigkeit des Abbaus von Nährstoffen wie Zucker und Fetten. Gleichzeitig verhindern sie eine Überproduktion freier Energie, die sonst Proteine in der Zelle denaturieren würde.
 
 <h4>Katalysatoren</h4>
 
 Ein Katalysator ist ein Stoff, der die Geschwindigkeit einer Reaktion durch Senkung der Aktivierungsenergie erhöht und sich dabei selbst wieder regeneriert. Ein Katalysator stellt einen alternativen Weg oder Mechanismus für eine Reaktion zur Verfügung und beschleunigt sowohl die Vorwärts-als auch die Umkehrreaktion. In der Biologie sind Enzyme Beispiele für Katalysatoren. Sie senken die Aktivierungsenergie für Reaktionen, die im Zellstoffwechsel benötigt werden.
 
 Zum Beispiel verstoffwechselt der Mensch Zucker und Fett zu Energie. Enzyme sind für den Menschen zum Abbau dieser Moleküle lebensnotwendig. Würde sich der Körper alleine Wärmeenergie zunutze machen, würde die, in Form von Wärme freigesetzte, freie Energie die Proteine in der Zelle denaturieren. Außerdem würde die Wärmeenergie unspezifisch alle Reaktionen katalysieren. Enzyme binden jedoch nur an bestimmte chemische Reaktionspartner, sogenannte Substrate. Ihre Aktivierungsenergie wird gesenkt, um spezifische zelluläre Reaktionen zu katalysieren.

Aktivierungsenergie

Aktivierungsenergie ist die minimale Energiemenge, die erforderlich ist, damit eine chemische Reaktion ablaufen kann. Je höher die Aktivierungsenergie, desto langsamer die Rate ...

Education

Lehre

JoVE Core

Biology

Biologie

Cellular Processes

Zelluläre Prozesse

Metabolism

Stoffwechsel

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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...

first law of thermodynamics

Energy Flow in a Food Web

Energy flow in a food web shows the First Law of Thermodynamics in action. Energy cannot be created or destroyed. It can only change form as it moves through living things and the environment. Sunlight is the starting point. Plants capture radiant energy from the sun during photosynthesis and turn it into chemical energy stored in complex carbohydrates. At the same time, oxygen is released into the atmosphere. Herbivores eat the plants and use those sugars during digestion. The energy is...

second law of thermodynamics

Entropy in Food Web Energy Flow

The Second Law of Thermodynamics explains why entropy increases as energy moves through a system. Entropy means the amount of disorder in a system. Each time energy is transferred or transformed, some energy is lost as unusable heat. That heat can raise the motion of nearby molecules for a short time and make the surroundings less ordered and more random. This idea also appears in a food web. Primary producers, such as plants, take in energy from the sun and make food. During this process,...

kinetic energy

Motion as a Source of Energy

Kinetic energy is the energy of motion. It appears when an object is moving and can do work or cause change. A waterfall is one clear example. Water behind a dam has potential energy, but when it rushes downward, that moving water has kinetic energy. When the water reaches the bottom and stops moving, its energy can become potential energy again. Kinetic energy also shows up in living systems. Plants absorb light particles, called photons, which move very fast and help create chemical energy...

potential energy

Stored Energy in Motion and Bonds

Stored energy in motion and bonds is called potential energy. It depends on the structure of an object or the position of matter in space. Raising a kettlebell changes its location and increases its potential energy. A stretched rubber band also stores potential energy, which can later change into kinetic energy. Chemical bonds between atoms hold another form of stored energy called chemical energy. These bonds involve attractive forces, and that energy can change into other forms during a...

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...

hydrolysis of atp

ATP Breakdown and Energy Release

ATP breakdown releases energy for cell work. Adenosine triphosphate, or ATP, can lose one or two phosphate groups when water is added. This hydrolysis reaction is exergonic, which means it releases energy that the cell can use. When one phosphate group is removed, ATP becomes ADP, or adenosine diphosphate. Inorganic phosphate is also released. ADP can then be hydrolyzed again to form AMP, or adenosine monophosphate, after a second phosphate group is removed. ATP has a clear structure. It is...

phosphorylation

Phosphorylation and Protein Control

Phosphorylation helps control how proteins work in cells. It is the addition or removal of phosphate groups, and it is the most common chemical change that regulates cellular processes. These changes can alter a protein’s structure, activity, stability, location inside the cell, and interactions with other proteins. During phosphorylation, protein kinases move the terminal phosphate group from ATP to a specific amino acid side chain on a target protein. The amino acids most often...

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

Allosteric control changes enzyme speed when a molecule binds to a site other than the active site. That alternate binding spot is called an allosteric site. An enzyme can have more than one allosteric site. This type of control can raise or lower enzyme activity. Many enzymes with allosteric control are metabolic enzymes. They help with the breakdown or the building of specific molecules in cells. In allosteric inhibition, the effector molecule causes a shape change that lowers the enzyme's...

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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