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

Les enzymes, qui sont en général des protéines,fonctionnent en se liant à un substrat,une molécule sur laquelle elles agissentde façon spécifique. 
Elles peuvent donc uniquement se lier à certains substrats. 
La propriété est principalement déterminée par la formeet les caractéristiques chimiques de leur site actif,la région de l'enzyme qui se lie au substrat. 
Selon le modèle de l'ajustement induitde l'activité de l'enzyme, cette liaison changela structure, la formede l'enzyme et du substrat. 
Le substrat se rapproche alorsd'un état de transition d'énergie plus élevéenécessaire pour que la réaction se produise. 
Par exemple, en affaiblissant ses liaisonspour qu'il puisse réagir plus facilement. 
Après avoir obtenu le produit de la réaction,l'enzyme est libérée et peut être utiliséepour de nouveau catalyser des réactions.

modèle à ajustement induit

Induced-fit Model

La plupart des réactions chimiques dans les cellules nécessitent des enzymes — des catalyseurs biologiques qui accélèrent la réaction sans être utilisés ou modifiés de façon permanente. Elles fonctionnent en réduisant l’énergie d’activation nécessaire pour que les réactifs soient transformés en produits. Les enzymes, qui sont habituellement des protéines, fonctionnent en se liant à un substrat — une molécule de réactif sur laquelle elles agissent.
 
 <h4>La spécificité</h4> 
 
 Les enzymes présentent une spécificité du substrat, ce qui signifie qu’elles ne peuvent se lier qu’à certains substrats. Ceci est principalement déterminé par la forme et les caractéristiques chimiques de leur site actif — la région de l’enzyme qui se lie au substrat.
 
 Selon l’activité enzymatique du modèle de l’ajustement induit, cette liaison modifie la conformation, ou la forme, de l’enzyme et du substrat. Cela rapproche le substrat de l’état de transition énergétique plus élevé nécessaire à la réaction, par exemple, en affaiblissant ses liaisons afin qu’il puisse réagir plus facilement. Les enzymes peuvent également accélérer une réaction en créant des conditions dans le site actif qui sont plus propices au déroulement de la réaction que le milieu cellulaire environnant.
 
 Une fois que les produits de la réaction sont formés, ils sont libérés du site actif et l’enzyme peut être utilisée pour catalyser des réactions encore une fois.

Modèle à ajustement induit

La plupart des réactions chimiques dans les cellules nécessitent des enzymes, des catalyseurs biologiques qui accélèrent la réaction sans être consommés ou modifiés de façon permanente. Ils...

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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.

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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.

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How Enzymes Adjust to Their Substrates

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