Name: electron carriers in cell energy transfer
Uploaded: 2023-04-30T10:09:20.000Z
Duration: 1 min 19 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Physical Science

SC.912.P.8

SC.912.P.8.10

oxidation-and-reduction-of-organic-molecules

Oxidation and Reduction of Organic Molecules

Les organismes vivants décomposent les molécules organiques dans une série de réactions pour générer de l’énergie. Beaucoup de ces réactions sont des réactions d’oxydoréduction ou des réactions d’oxydoréduction.
L’oxydation est l’élimination d’électrons d’un atome, tandis que la réduction est l’ajout d’électrons. Parce que le nombre d’électrons dans une réaction est conservé, les demi-réactions d’oxydation et de réduction se produisent toujours par paires.
À l’intérieur des cellules, lorsqu’une molécule gagne un électron, elle accepte souvent un proton de son environnement. Cet ajout d’hydrogène s’appelle l’hydrogénation, et la molécule est réduite. À l’inverse, lorsqu’une molécule perd des hydrogènes, il s’agit d’une déshydrogénation, et la molécule est oxydée.
Les protons et les électrons peuvent être transférés à des molécules porteuses d’électrons, y compris les coenzymes.
Par exemple, lors de la déshydrogénation du succinate en fumarate, les électrons et les protons sont transférés à la coenzyme FAD, la réduisant à FADH2. Le FADH2 réduit transfère ensuite les électrons à travers la chaîne de transport d’électrons et est oxydé en FAD.

les réactions d’oxydation et de réduction des molécules organiques

La production d'énergie au sein d'une cellule implique de nombreuses voies chimiques coordonnant les unes avec les autres . La plupart de ces voies sont des combinaisons de réactions d’oxydation et de réduction qui se produisent simultanément. Une réaction d’oxydation enlève un électron à un atome d’un composé, et l’ajout de cet électron à un autre composé est dite une réaction de réduction. Étant donné que l’oxydation et la réduction se produisent généralement ensemble, ces paires de réactions sont appelées “réactions redox”.

La suppression d’un électron d’une molécule entraîne une diminution de l’énergie potentielle du composé oxydé. Cependant, l’électron (parfois faisant partie d’un atome d’hydrogène) ne reste pas libre dans le cytoplasme de la cellule. Au lieu de cela, il est déplacé vers un deuxième composé, le réduisant ainsi. Le déplacement d'un électron d'un composé vers un autre supprime une partie de l'énergie potentielle du premier composé (le composé oxydé) et augmente celle du deuxième (le composé réduit). Le transfert d’électrons entre molécules est important car la majeure partie de l’énergie stockée dans les atomes et utilisée pour alimenter les fonctions cellulaires se présente sous forme d’électrons de haute énergie. Le transfert d’énergie sous la forme d’électrons de haute énergie permet à la cellule de transférer et d’utiliser l’énergie de manière progressive, par petits paquets plutôt que par une seule rafale destructrice.

Au sein des systèmes vivants, une petite classe de composés fait office de navettes électroniques : liant et transportant des électrons de haute énergie entre les composés impliqués dans des voies biochimiques. Les principaux porteurs d’électrons dont nous allons parler sont issus du groupe des vitamines B et sont des dérivés de nucléotides. Ces composés peuvent être facilement réduits (c’est-à-dire qu’ils acceptent des électrons) ou oxydés (ils perdent des électrons). Le nicotinamide adénine dinucléotide (NAD) est dérivé de la vitamine B3, la niacine. NAD+ est la forme oxydée de la molécule ;tandis que  le NADH en est la forme réduite après que celle-ci ait accepté deux électrons et un proton (qui, ensemble, sont l'équivalent d'un atome d'hydrogène avec un électron supplémentaire).

Ce texte est adapté de <a href="https://openstax.org/books/biology-2e/pages/7-1-energy-in-living-systems">Openstax, Biology 2e, Section 7.1 Energy in Living Systems</a>

Les réactions d’oxydation et de réduction des molécules organiques

La production d’énergie à l’intérieur d’une cellule implique de nombreuses voies chimiques coordonnées. La plupart de ces voies sont des combinaisons de réactions d’oxydation et de réduction, ...

Education

Enseignement

JoVE Core

Cell Biology

Biologie cellulaire

Unit 1

Unité 1

Energy and Catalysis

Énergie et catalyse

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

electron carriers in cell energy transfer

Cell energy production depends on redox reactions, which are oxidation and reduction reactions that happen together. In oxidation, an electron is removed from an atom in a compound. In reduction, that same electron is added to another compound. Because these reactions usually occur as a pair, they are called redox reactions.

When a molecule loses an electron, its potential energy goes down. The electron does not stay free in the cytoplasm. Instead, it moves to a second compound and reduces that compound. This transfer lowers the energy of the oxidized compound and raises the energy of the reduced compound.

Electron transfer matters because much of the energy stored in atoms and used for cell functions is carried by high-energy electrons. Cells pass this energy along in small steps rather than in one large burst. That makes energy transfer more controlled and less destructive.

Living systems use a small group of compounds as electron shuttles. These carriers bind high-energy electrons and move them between compounds in biochemical pathways. The main carriers discussed here are derived from B vitamins and are nucleotide derivatives. They can be reduced when they accept electrons or oxidized when they lose electrons.

One key example is nicotinamide adenine dinucleotide, or NAD. NAD comes from vitamin B3, also called niacin. NAD+ is the oxidized form. NADH is the reduced form after it accepts two electrons and a proton, which together are the equivalent of a hydrogen atom with an extra electron.

Electron Carriers in Cell Energy Transfer

electron-carriers-in-cell-energy-transfer

the first law of thermodynamics

Energy Changes in Cells and Matter

The first law of thermodynamics describes how energy changes form in the universe. The total amount of energy stays constant. Energy can move from one place to another or change into a different form, but it cannot be created or destroyed. These energy changes happen in everyday life. A light bulb changes electrical energy into light energy. A gas stove changes chemical energy in natural gas into heat energy. Plants also carry out a major energy transformation when they convert sunlight energy...

the second law of thermodynamics

Entropy and Spontaneous Change

Entropy helps predict whether a process will happen on its own. Entropy is a measure of randomness or disorder in a system. High entropy means high disorder and low energy. A student’s bedroom is a simple example. If no work is done, the room becomes messy over time. That messy state is highly disordered and has high entropy. To make the room clean again, energy must be added as the student puts things away. That organized state has low entropy. Processes that increase the entropy of the...

enthalpy within the cell

Cellular Enthalpy and Energy Changes

Cellular enthalpy describes how heat and energy change during chemical and physical processes. Enthalpy is written as H and is defined as the sum of a system’s internal energy, U, and the product of pressure and volume, PV. It is a state function, which means its value depends on the state of the system, not the path taken. Scientists cannot measure the enthalpy of a single substance directly. They can determine enthalpy changes, or ΔH, for a process instead. For reactions or changes that...

entropy within the cell

Cell Energy Loss and Entropy

Cell energy loss and entropy explain why living things need constant energy input. Cells obtain energy, transform it, and use it to do work, but these transfers are never completely efficient. In each transfer, some energy is lost in a form that cannot be used. In many cases, that lost energy is heat energy.

an introduction to free energy

Gibbs Free Energy and Reaction Work

Gibbs free energy describes the usable energy in a chemical reaction. It helps scientists compare how much energy different reactions release. This measurement is called Gibbs free energy, or G, after Josiah Willard Gibbs. The second law of thermodynamics explains why not all energy stays available for work. Some energy is lost in an unusable form, such as heat, and this loss increases entropy. Gibbs free energy is the energy left after that entropy loss is taken into account. Every chemical...

endergonic and exergonic reactions in the cell

endergonic-and-exergonic-reactions-in-the-cell

Cell Reactions That Release or Store Energy

Cell reactions can either release energy or store it for later use. In chemistry, this difference is described by the value of ΔG, or free energy change. When energy is released during a reaction, ΔG is negative. The products then have less free energy than the reactants because some free energy has been given off. Reactions with a negative ΔG are called exergonic reactions. Exergonic means energy is leaving the system. These reactions are also called spontaneous reactions because they can...

the equilibrium binding constant and binding strength

the-equilibrium-binding-constant-and-binding-strength

How Equilibrium Binding Constant Affects Binding

The equilibrium binding constant describes how strongly two molecules bind at equilibrium. It is a useful way to compare binding strength in molecular interactions. This topic focuses on how binding is measured and what the equilibrium binding constant means. A higher value indicates stronger binding, while a lower value indicates weaker binding. Understanding this constant helps explain how tightly molecules stay together under equilibrium conditions. The page also connects the binding...

free energy and equilibrium

Free Energy and Reaction Direction

Free energy and reaction direction are linked in chemical equilibrium. A free energy change, ΔG, shows the driving force for a process. When ΔG is negative, the process is driven forward. When ΔG is positive, the reverse direction is favored. When ΔG is zero, the forward and reverse driving forces are equal, and the system is at equilibrium. The reaction quotient, Q, helps show how close a system is to equilibrium. Q is the numerical value of the mass action expression for the system. It can...

non-equilibrium in the cell

Cells Stay Out of Equilibrium

Cells stay out of chemical equilibrium by constantly using energy and moving materials in and out. Chemical reactions in metabolism are often reversible. They can go in both directions. In one direction, they release energy to the surroundings. In the reverse direction, they absorb energy. The same idea applies to reactions that build and break down cell molecules. Proteins, for example, can be broken into individual amino acids, and amino acids can be used to build proteins again. In a closed...

oxidation and reduction of organic molecules

Cell energy production depends on redox reactions, which are oxidation and reduction reactions that happen together. In oxidation, an electron is removed from an atom in a compound. In reduction, that same electron is added to another compound. Because these reactions usually occur as a pair, they are called redox reactions. When a molecule loses an electron, its potential energy goes down. The electron does not stay free in the cytoplasm. Instead, it moves to a second compound and reduces...

introduction to enzymes

Enzyme Function, Cofactors, and Inhibitors

Enzymes are proteins that speed up biochemical reactions without being used up. Humans have used enzymes since about 7000 BCE, when they fermented sugars to make alcohol without knowing the reaction was enzyme-catalyzed. The word enzyme was coined by Wilhelm Kuhne in 1877. It comes from the Greek words en, meaning “in” or “within,” and zyme, meaning “yeast.” Enzymes work through active sites, which are regions that bind substrates and help convert them into products. Many enzymes also have...

enzymes and activation energy

How Enzymes Lower Reaction Energy

Enzymes lower the energy needed for a chemical reaction to begin. That starting energy is called activation energy, or free energy of activation, and it is often written as Ea. During a reaction, bonds break and new bonds form. In glucose breakdown, for example, bonds between carbon atoms break and release energy because they are energy-storing bonds. Before a reaction can move forward, reactant molecules must reach a high-energy, unstable shape called the transition state. To get there, the...

introduction to enzyme kinetics

Graphing Enzyme Kinetics Data

Enzyme kinetics uses graphs to show how fast a biochemical reaction happens. Scientists measure the initial reaction rate, or velocity (Vo), at different substrate concentrations ([S]). They may also run trials with inhibitors or other molecules that change the reaction rate. The results are often plotted as Vo against [S]. For many single-substrate reactions, the data fits the Michaelis-Menten equation. This equation, named after Leonor Michaelis and Maud Menten, helps estimate the maximum...

turnover number and catalytic efficiency

How Fast Enzymes Work in Digestion

Enzymes can work at very different speeds, and their turnover number shows how fast they convert substrate molecules into products. Turnover number is the maximum number of substrate molecules an enzyme can transform per unit time. For most enzymes, this value is between 1 and 1000 molecules per second. Some enzymes are especially fast. Catalase has the highest known turnover number and can convert up to 2.8×10^6 molecules of hydrogen peroxide into water and oxygen each second. Lysozyme has...

catalytically perfect enzymes

Diffusion-Controlled Enzymes and Reaction Speed

Catalytically perfect enzymes are enzymes that speed up biochemical reactions at very high rates. The idea was first proposed by W. J. Albery and J. R. Knowles in 1976. These enzymes have catalytic efficiency values of about 10^8 to 10^9 M^-1 s^-1 and are also called diffusion-controlled enzymes because diffusion of the substrate into the active site is the only rate-limiting step. Examples of catalytically perfect enzymes include triose phosphate isomerase, fumarase, and superoxide dismutase.

introduction to mechanisms of enzyme catalysis

introduction-to-mechanisms-of-enzyme-catalysis

How Enzymes Change Shape to Catalyze

Enzyme catalysis depends on how enzymes bind substrates and how the active site responds during the reaction. Scientists once described this process with a simple lock-and-key model, where the enzyme and substrate fit together in one instant. Research now supports induced fit, a more dynamic model in which binding causes a small change in the enzyme’s shape. That shift helps create an ideal match between the enzyme and the substrate’s transition state, which improves catalysis. The active site...

ligand binding and linkage

Ligand Binding and Allosteric Effects

Ligand binding and linkage describe how one molecule can affect another when it binds to a protein. In this topic, the focus is on how binding at one site can influence activity at a different site on the same protein. This idea is important for understanding protein function in high school biology. It helps explain why some proteins respond more strongly after a ligand attaches. The transcript centers on the connection between ligand binding and linkage, which is a key concept in molecular...

cooperative allosteric transitions

How Proteins Shift Shape Together

Proteins can change shape in a coordinated way during allosteric transitions. In a cooperative transition, one part of the protein affects another part, so the change spreads through the molecule. These shape changes help proteins switch between different states. The shift can influence how the protein works and how it responds to other molecules. Cooperative allosteric transitions are an important idea in protein function. They explain how a small change at one site can lead to a larger...

ribozymes

Catalytic RNA: Ribozymes in Action

Ribozymes are RNA molecules that can act as enzymes. They help speed up specific chemical reactions without being protein enzymes. This makes them an important example of RNA with more than one job in the cell. Some ribozymes can cut RNA molecules, and others can join them together. This shows that RNA can do catalytic work as well as carry genetic information. Ribozymes are a key part of how scientists think about the many roles of RNA in biology. One well-known ribozyme is ribonuclease P,...

atp energy storage and release

ATP Powers Cellular Transport and Reactions

ATP powers cellular transport and many reactions by transferring energy through phosphorylation. ATP is a highly unstable molecule. If it is not used quickly, it breaks down into ADP and inorganic phosphate, and the released energy is lost as heat. Cells use ATP through energy coupling. This means the exergonic reaction of ATP hydrolysis is linked to an endergonic reaction so the reaction can move forward. One major example is the sodium-potassium pump, a transmembrane ion pump that is vital...

atp and macromolecule synthesis

ATP in Building Cell Macromolecules

ATP helps cells build biological macromolecules. These organic compounds are mainly made of carbon atoms bonded to hydrogen, oxygen, nitrogen, and small amounts of other elements. The four major classes of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids. Most macromolecules start as small subunits called monomers. Cells join monomers with covalent bonds to make larger molecules called polymers. This building process needs energy, so cells depend on ATP, the...

coupled reactions

ATP Powers Cellular Work

ATP powers many kinds of cellular work by coupling energy-releasing reactions to energy-requiring ones. Some reactions happen on their own and release energy. Others need an energy input to move forward. Cells link these reactions so important processes can still occur. Adenosine triphosphate, or ATP, stores energy that cells can use quickly. ATP hydrolysis is the breaking of ATP, and it releases energy. Cells often use that released energy to drive endergonic reactions, which are reactions...

key terms and concepts

Learn how redox reactions move electrons in cells and how NAD and NADH act as electron carriers in energy transfer for high school biology.

Electron Carriers in Cell Energy Transfer | JoVE K12

cell biology

JoVE Core Biologie cellulaire illustre les processus cellulaires complexes dans des leçons vidéos complètes mais faciles à comprendre. Cette collection se concentre sur les composants et fonctions essentiels de la cellule ; cela inclut les organelles et les membranes ainsi que le transport et le métabolisme énergétique cellulaire. Elle est complétée par nos vidéos de scientifiques à l'action qui démontrent l'application de la biologie cellulaire dans des expériences concrètes.

Classifying Matter by State

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States of Matter

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States of Matter and Phase Changes

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Differentiate between physical and chemical properties and physical and chemical changes of matter.

SC.912.P.8.1

physical-and-chemical-properties-of-matter

Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

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Phase Transitions

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Phase Transitions: Vaporization and Condensation

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Vapor Pressure

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Clausius-Clapeyron Equation

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Phase Diagrams

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SC.912.P.8.2

The Atomic Theory of Matter

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Subatomic Particles

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Emission Spectra

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The de Broglie Wavelength

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The Quantum-Mechanical Model of an Atom

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Explore the scientific theory of atoms (also known as atomic theory) by describing changes in the atomic model over time and why those changes were necessitated by experimental evidence.

SC.912.P.8.3

Elements: Chemical Symbols and Isotopes

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Ions and Ionic Charges

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Atomic Mass

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SC.912.P.8.4

Periodic Classification of the Elements

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Electron Configurations

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Electron Behavior

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atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

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Atomic Orbitals

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The Pauli Exclusion Principle

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The Energies of Atomic Orbitals

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electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

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SC.912.P.8.5

Types of Chemical Bonds

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SC.912.P.8.6

A. A working definition of matter is that it takes up space, has mass, and has measurable properties. Matter is comprised of atomic, subatomic, and elementary particles.

B. Electrons are key to defining chemical and some physical properties, reactivity, and molecular structures. Repeating (periodic) patterns of physical and chemical properties occur among elements that define groups of elements with similar properties. The periodic table displays the repeating patterns, which are related to the atom's outermost electrons. Atoms bond with each other to form compounds.

C. In a chemical reaction, one or more reactants are transformed into one or more new products. Many factors shape the nature of products and the rates of reaction. 

D. Carbon-based compounds are building-blocks of known life forms on earth and numerous useful natural and synthetic products.

Electron Carriers in Cell Energy Transfer

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