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

W wielu przypadkach enzymy wymagają do działania dodatkowych cząsteczek - zwanych kofaktorami. Te cząsteczki pomocnicze można sklasyfikować jako jony metali lub organiczne, niebiałkowe cząsteczki. 

Na przykład podczas pierwszego etapu glikolizy kofaktor magnez wiąże się z ATP, zacieśniając wiązanie między dwiema grupami fosforanowymi. Działanie to pozwala na łatwiejsze uwolnienie ostatniej grupy fosforanowej przez enzym heksokinazę, przekształcając glukozę w 6-fosforan glukozy. Dlatego magnez, jako kofaktor, wiąże się z ATP i zwiększa jego efektywność. 

Drugi podzbiór kofaktorów – koenzymy – to związki organiczne, zwykle pochodne witamin.  

Na przykład witamina C jest ważnym koenzymem w syntezie kolagenu białkowego. Kiedy hydroksylaza wiąże się z kolagenem, witamina C ułatwia hydroksylację reszt na kolagenie. Za pomocą witaminy C hydroksylaza wspomaga zmianę kształtu kolagenu do jego końcowej struktury potrójnej helisy, która jest niezbędna do utrzymania ważnych tkanek ciała.

Tong, Liang. "Struktura i funkcja karboksylaz zależnych od biotyny." Nauki o Życiu Komórkowym i Molekularnym 70, nr 5 (2013): 863-891. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3508090/">Źródło</a>]

Yang, Wei, Jae Young Lee i Marcin Nowotny. "Wytwarzanie i rozbijanie kwasów nukleinowych: kataliza dwu-Mg2+-jonowa i specyficzność substratu." Komórka Molekularna 22, nr 1 (2006): 5-13. [<a href="https://doi.org/10.1016/j.molcel.2006.03.013">Źródło</a>]

kofaktory i koenzymy

Cofactors and Coenzymes

Enzymy wymagają dodatkowych składników do prawidłowego funkcjonowania. Istnieją dwie takie klasy cząsteczek: kofaktory i koenzymy. Kofaktorami są jony metali, a koenzymy to niebiałkowe cząsteczki organiczne. Obydwa typy cząsteczek pomocniczych mogą być ściśle związane z enzymem lub wiązane tylko wtedy, gdy wiąże się substrat.

Kofaktory występują w ~30% dojrzałych białek. Często są włączane do enzymu podczas jego składania i biorą udział w aktywności katalitycznej enzymu. Magnez jest niezbędnym kofaktorem ponad 300 enzymów w organizmie człowieka, w tym polimerazy DNA. W tym przypadku jon magnezu pomaga w tworzeniu wiązania fosfodiestrowego w szkielecie DNA. Żelazo, miedź, kobalt i mangan to inne popularne kofaktory.

Wiele witamin to koenzymy, ponieważ są to niebiałkowe, organiczne cząsteczki pomocnicze dla enzymów. Na przykład biotyna — rodzaj witaminy B — odgrywa ważną rolę w różnych enzymach przenoszących dwutlenek węgla z jednej cząsteczki na drugą.  Biotyna, witamina A i inne witaminy muszą być spożywane w naszej diecie, ponieważ ludzkie komórki nie mogą ich wytworzyć.

Kofaktory i koenzymy

Enzymy wymagają dodatkowych składników do prawidłowego funkcjonowania. Istnieją dwie takie klasy cząsteczek: kofaktory i koenzymy. Kofaktory to jony metali ...

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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

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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Energy flow in a food web shows the First Law of Thermodynamics in action. Energy cannot be created or destroyed. It can only change form as it moves through living things and the environment. Sunlight is the starting point. Plants capture radiant energy from the sun during photosynthesis and turn it into chemical energy stored in complex carbohydrates. At the same time, oxygen is released into the atmosphere. Herbivores eat the plants and use those sugars during digestion. The energy is...

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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,...

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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...

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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 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...

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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...

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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...

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Competitive vs Noncompetitive Inhibitors

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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 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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