Name: enzyme helpers: metals, vitamins, and more
Uploaded: 2019-07-31T14:21:57.000Z
Duration: 1 min 27 s
Channel: JoVE

- [Instructeur] Dans de nombreux cas, les enzymes ont besoinde molécules supplémentaires,appelées cofacteurs, pour fonctionner. 
Ces molécules auxiliaires peuvent être classées comme desions métalliques ou des molécules organiques non protéiques. 
Par exemple, au cours de la première étape de la glycolyse,le cofacteur magnésium se lie à l'ATP,resserrant la liaison entre deux des groupes phosphate. 
Cette action permet au dernier groupe phosphated'être libéré plus facilement par l'enzyme hexokinase,transformant le glucose en glucose 6-phosphate. 
Par conséquent, le magnésium,en tant que cofacteur, se lie àl'ATP et augmente son efficacité. 
Les autres cofacteurs, les coenzymes,sont des composés organiquesgénéralement des dérivés de vitamines. 
Par exemple, la vitamine C est un coenzyme importantdans la synthèse de la protéine collagène. 
Lorsque le collagène se lie à son enzyme hydroxylase,la vitamine C se lie à l'enzymeet donne un groupe hydroxyle. 
Maintenant, l'hydroxylase hydrolysée peut aiderà changer la forme du collagèneen sa structure finale à triple hélice,essentielle au maintiendes tissus corporels importants.

Tong, Liang. « Structure et fonction des carboxylases dépendantes de la biotine. » Sciences de la vie cellulaire et moléculaire 70, n° 5 (2013) : 863-891. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3508090/">Source</a>]

Yang, Wei, Jae Young Lee et Marcin Nowotny. « Fabrication et décomposition des acides nucléiques : catalyse à deux ions Mg2+ et spécificité du substrat. » Molecular Cell 22, n° 1 (2006) : 5-13. [<a href="https://doi.org/10.1016/j.molcel.2006.03.013">Source</a>]

cofacteurs et coenzymes

Cofactors and Coenzymes

Les enzymes ont besoin de composants supplémentaires pour bien fonctionner. Il existe deux catégories de molécules de ce type : les cofacteurs et les coenzymes. Les cofacteurs sont des ions métalliques et les coenzymes sont des molécules organiques non protéiques. Ces deux types de molécules auxiliaires peuvent être fortement liés à l’enzyme ou liés seulement lorsque le substrat se lie.
 
 Les cofacteurs sont présents dans environ 30 % des protéines matures. Ils sont fréquemment incorporés dans une enzyme alors qu’elle est repliée et ils sont impliqués dans l’activité catalytique de l’enzyme. Le magnésium est un cofacteur essentiel pour plus de 300 enzymes dans le corps humain, y compris la polymérase d’ADN. Dans ce cas, l’ion magnésium aide à la formation de la liaison phosphodiester sur le squelette de l’ADN. Le fer, le cuivre, le cobalt et le manganèse sont d’autres cofacteurs courants.
 
 Beaucoup de vitamines sont des coenzymes car ce sont des molécules auxiliaires organiques non protéiques pour les enzymes. Par exemple, la biotine — un type de vitamine B — est importante dans une variété d’enzymes qui transfèrent le dioxyde de carbone d’une molécule à l’autre.  La biotine, la vitamine A et d’autres vitamines doivent être ingérées par le biais de notre alimentation car elles ne peuvent pas être fabriquées par des cellules humaines.

Cofacteurs et coenzymes

Les enzymes nécessitent des composants supplémentaires pour fonctionner correctement. Il existe deux classes de molécules : les cofacteurs et les coenzymes. Les cofacteurs sont des ions métalliques...

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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 300 enzymes in the human body, including DNA polymerase. In DNA polymerase, magnesium helps form the phosphodiester bond in the DNA backbone. Iron, copper, cobalt, and manganese are other common cofactors.

Many coenzymes come from vitamins. These organic helper molecules assist enzymes during reactions. Biotin, which is a B vitamin, helps several enzymes move carbon dioxide from one molecule to another. Vitamin A and other vitamins must come from the diet because human cells cannot make them.

Enzyme Helpers: Metals, Vitamins, and More

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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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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...

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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

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

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cofactors and coenzymes

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 cofactors and coenzymes help enzymes work, from magnesium in DNA polymerase to biotin and other vitamin-based helpers.

Enzyme Helpers: Metals, Vitamins, and More | JoVE K12

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Enzyme Helpers: Metals, Vitamins, and More

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