Name: how enzymes adjust to their substrates
Uploaded: 2019-03-11T09:21:10.000Z
Duration: 1 min 13 s
Channel: JoVE

الانزيمات والتي عادة ما تكون بروتينات تعمل من خلال الربط مع ركيزة،وهي الجزيئات التي تعمل عليها ولها خصائص مؤثرة عليها. وهذا يعني أنها لا ترتبط إلا بركائز محددة. يتم تحديد هذه الخاصية بشكل أساسي حسب الشكل والخصائص الكيميائية لموقعها النشط،وهي منطقة الانزيم الذي يرتبط عندها بالركيزة.بما يتوافق مع نموذج الانزيم الناجم عن النشاط،هذا الربط يغير التكوين،وهو شكل كل من الانزيم والركيزة. وهذا يجعل الركيزة أقرب إلى حالة الانتقال ذات طاقة أعلى اللازمة لحدوث التفاعل. على سبيل المثال،من خلال إضعاف روابطها بحيث يمكن أن تتفاعل بسهولة أكبر.بعد إنتاج ناتج التفاعل،يتم إطلاق الإنزيم ويمكن استخدامه لتحفيز تفاعلات مرة أخرى.

نموذج الملاءمة المستحَثّ

Induced-fit Model

تتطلب معظم التفاعلات الكيميائية في الخلايا تتطلب إنزيمات _ و هي محفزات بيولوجية تسرع التفاعل دون استهلاكها أو تغييرها بشكل دائم. إنها تعمل عن طريق تقليل طاقة التنشيط اللازمة لتحويل المواد المتفاعلة إلى منتجات. تعمل الإنزيمات ، التي تكون عادةً بروتينات ، عن طريق الارتباط بركيزة _ جزيء متفاعل تعمل عليه.

<h4>خصوصيه</h4>

تُظهر الإنزيمات خصوصية الركيزة ، مما يعني أنها يمكن أن ترتبط فقط بركائز معينة. يتم تحديد ذلك بشكل أساسي من خلال الشكل والخصائص الكيميائية لموقعها النشط _ منطقة الإنزيم التي ترتبط بالركيزة.

وفقاً لنموذج الملاءمة المستحثة لنشاط الإنزيم ، يغير هذا الارتباط التشكل _ أو الشكل _ لكل من الإنزيم والركيزة. هذا يجعل الركيزة أقرب إلى حالة انتقال الطاقة الأعلى اللازمة لحدوث التفاعل ، على سبيل المثال ، عن طريق إضعاف روابطها بحيث يمكن أن تتفاعل بسهولة أكبر. قد تسرع الإنزيمات أيضاً التفاعل عن طريق خلق ظروف داخل الموقع النشط تكون أكثر ملاءمة لاستمرار التفاعل من البيئة الخلوية المحيطة.

بمجرد تكوين نواتج التفاعل ، يتم إطلاقها من الموقع النشط ويمكن استخدام الإنزيم لتحفيز التفاعلات مرة أخرى.

تتطلب معظم التفاعلات الكيميائية في الخلايا إنزيمات - محفزات بيولوجية تسرع التفاعل دون استهلاكها أو تغييرها بشكل دائم. هم...

Education

JoVE Core

Biology

علم الأحياء

Cellular Processes

العمليات الخلوية

Metabolism

عملية التمثيل الغذائي (الأيض)

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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 features of the enzyme’s active site, the region that binds the substrate.

The induced-fit model explains what happens after the substrate binds. The binding changes the enzyme’s shape, or conformation. This change helps bring the substrate closer to the higher-energy transition state needed for the reaction, such as by weakening bonds so the substrate can react more easily.

Enzymes can also make the active site a better place for the reaction than the surrounding cell environment. After the products form, they leave the active site. The enzyme can then catalyze the reaction again.

How Enzymes Adjust to Their Substrates

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

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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

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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

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...

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

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

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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 enzyme active sites change shape in the induced-fit model, helping substrates reach the transition state and reactions happen faster.

How Enzymes Adjust to Their Substrates | JoVE K12

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How Enzymes Adjust to Their Substrates

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