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

Em um processo regulatório chamado de inibição por feedback, o produto de uma reação inibe uma enzima em uma etapa anterior na via metabólica que o produziu, assim diminuindo ou encerrando sua própria produção. O produto faz isso por meio de uma ligação a um sítio regulador na enzima, que é distinto do sítio ativo que se liga ao substrato. Quando o produto se liga ao sítio regulador, causa uma mudança conformacional na enzima que o inibe de continuar a catalisar a reação.Esta atividade impede que níveis excessivamente altos do produto se acumulem. E uma vez que o nível cai o suficiente, o produto não inibe mais a enzima e a produção pode continuar normalmente.

Sander, Timur, Niklas Farke, Christoph Diehl, Michelle Kuntz, Timo Glatter e Hannes Link. "A inibição do feedback alostérico permite a biossíntese robusta de aminoácidos em E. coli, reforçando a superabundância enzimática." Cell Systems 8, nº 1 (23 de janeiro de 2019): 66-75.e8. [<a href="https://doi.org/10.1016/j.cels.2018.12.005" target="__blank">Fonte</a>]

Bulfer, Stacie L., Erin M. Scott, Lorraine Pillus e Raymond C. Trievel. "Base estrutural para a inibição do feedback da L-lisina da homocitrato sintase." The Journal of Biological Chemistry 285, nº 14 (2 de abril de 2010): 10446–53. [<a href="https://doi.org/10.1074/jbc.M109.094383" target="__blank">Fonte</a>]

inibição de feedback

Feedback Inhibition

As reações bioquímicas ocorrem constantemente nas células, convertendo substâncias iniciais em diferentes produtos, geralmente com a ajuda de enzimas que aceleram as reações. Sem enzimas, levaria demasiado tempo para que a maioria das reações ocorresse de forma a terem utilidade para a célula!
 
 Uma vez que as enzimas ajudam a controlar a velocidade das reações, a sua atividade é regulada para que se mantenha quantidades adequadas de materiais iniciais, metabolitos intermediários e produtos na célula. A acumulação excessiva ou esgotamento de substâncias pode ter consequências desastrosas na saúde da célula e do organismo.
 
 Em um processo regulatório chamado inibição de feedback, o produto de uma reação inibe uma enzima de um passo anterior na via metabólica que o produziu. O produto liga-se a um local regulatório na enzima, que é distinto do local ativo onde se liga o substrato, retardando ou desligando a sua própria produção. Quando o produto se liga ao local regulatório, causa uma mudança conformacional na enzima que a impede de se ligar ao substrato e continuar a catalisar a reação.
 
 Isso evita que níveis excessivamente altos do produto se acumulem na célula. Quando o seu nível diminui o suficiente, o produto deixa de inibir a enzima, e a reação pode continuar normalmente.

Inibição de Feedback

As reações bioquímicas estão ocorrendo constantemente nas células, convertendo substâncias iniciais em diferentes produtos, geralmente com a ajuda de enzimas que aceleram ...

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TERMOS-CHAVE E CONCEITOS

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...

first law of thermodynamics

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free energy

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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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hydrolysis of atp

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induced-fit model

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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

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

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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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