Name: how cells control product buildup
Uploaded: 2019-03-11T09:21:10.000Z
Duration: 46 s
Channel: JoVE

- [Instructeur] Dans un processus de régulationqu'on appelle rétro-inhibition,le produit d'une réaction inhibe une enzymeà une étape antérieure du processus métaboliquequi l'a produite, ralentissant ou arrêtant ainsisa propre production. 
Pour ce faire, le produit se lie à un site régulateursur l'enzyme, différent du site actifqui se lie au substrat. 
Quand le produit se lie au site régulateur,il provoque un changement conformationnel de l'enzymequi l'empêche de continuer à catalyser la réaction. 
Cette activité empêche l'accumulationdu produit à des niveaux excessivement élevés. 
Une fois le niveau suffisamment descendu,Le produit n'inhibe plus l'enzyme,et la production peut reprendre.

Sander, Timur, Niklas Farke, Christoph Diehl, Michelle Kuntz, Timo Glatter et Hannes Link. « L’inhibition de la rétroaction allostérique permet une biosynthèse robuste des acides aminés chez E. coli en renforçant la surabondance d’enzymes. » Cell Systems 8, n° 1 (23 janvier 2019) : 66-75.e8. [<a href="https://doi.org/10.1016/j.cels.2018.12.005 » target="__blank">Source</a>]

Bulfer, Stacie L., Erin M. Scott, Lorraine Pillus et Raymond C. Trievel. « Base structurelle de l’inhibition de la rétroaction L-lysine de l’homocitrate synthase. » The Journal of Biological Chemistry 285, n° 14 (2 avril 2010) : 10446-53. [<a href="https://doi.org/10.1074/jbc.M109.094383 » target="__blank">Source</a>]

inhibition de rétroaction

Feedback Inhibition

Les réactions biochimiques se produisent constamment dans les cellules, transformant les substances de départ en différents produits, généralement à l’aide d’enzymes qui accélèrent les réactions. Sans enzymes, il faudrait beaucoup trop de temps pour que la plupart des réactions se produisent afin d’être utiles à la cellule !
 
 Puisque les enzymes aident à contrôler la vitesse des réactions, leur activité est régulée pour que des quantités appropriées de matériaux de départ, de métabolites intermédiaires et de produits soient maintenus dans la cellule. L’accumulation excessive ou l’épuisement des substances peut avoir des conséquences désastreuses sur la santé de la cellule et de l’organisme.
 
 Dans un mécanisme de régulation appelé rétro-inhibition, le produit d’une réaction inhibe une enzyme à une étape antérieure dans la voie métabolique qui l’a produit. Le produit se lie à un site de régulation sur l’enzyme, qui est distinct du site actif qui se lie au substrat, ralentissant ou arrêtant ainsi sa propre production. Lorsque le produit se lie au site de régulation, il provoque un changement conformationnel dans l’enzyme qui l’empêche de se lier au substrat et de continuer à catalyser la réaction.
 
 Cela empêche que des niveaux excessivement élevés du produit s’accumulent dans la cellule. Lorsque son niveau est assez bas, le produit n’inhibe plus l’enzyme et la réaction peut se poursuivre comme d’habitude.

Inhibition de rétroaction

Des réactions biochimiques se produisent constamment dans les cellules, convertissant les substances de départ en différents produits, généralement à l’aide d’enzymes qui accélèrent ...

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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 control process is feedback inhibition. In this process, the final product of a reaction slows an enzyme from an earlier step in the same pathway.

The product binds to a regulatory site on the enzyme. This site is different from the active site, which is where the substrate normally binds. Binding at the regulatory site changes the enzyme’s shape. That conformational change prevents the enzyme from binding the substrate and keeps the reaction from continuing.

Feedback inhibition helps stop too much product from accumulating in the cell. When product levels fall, the product no longer inhibits the enzyme. The pathway can then start again and continue producing the molecule as needed.

How Cells Control Product Buildup

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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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...

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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...

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enzyme kinetics

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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

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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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 feedback inhibition lets cells regulate enzymes, stop product buildup, and keep metabolic reactions balanced in high school biology.

How Cells Control Product Buildup | JoVE K12

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How Cells Control Product Buildup

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