Name: cellular enthalpy and energy changes
Uploaded: 2023-04-30T10:40:59.000Z
Duration: 1 min 18 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Biology

BIO.11

BIO.11.A

Enthalpy within the Cell

L’énergie interne, ou E, est l’énergie contenue dans un système, telle que l’énergie contenue dans les liaisons chimiques et le mouvement aléatoire de ses particules. Un système et son environnement peuvent transférer de l’énergie entre eux.
La variation de l’énergie interne d’un système, delta E, est égale à la somme de q, la chaleur totale transférée au système, et w, le travail total effectué sur le système.
Dans la plupart des réactions biochimiques, aucun travail n’est effectué ; par conséquent, la variation de l’énergie interne est équivalente à une autre fonction thermodynamique appelée enthalpie.
La variation d’enthalpie d’un système ou d’un ∆H s’accompagne d’une variation égale et opposée de l’enthalpie de l’environnement.
Un processus exothermique se produit lorsque le système libère de la chaleur dans l’environnement et est représenté par une enthalpie négative. Un processus endothermique se produit lorsque le système gagne de la chaleur, représentée par une enthalpie positive.
Les cellules vivantes sont des systèmes ouverts qui échangent de la matière et de l’énergie avec leur environnement, par des processus exothermiques et endothermiques, selon la première loi de la thermodynamique.

enthalpie dans la cellule

L'enthalpie (H) est utilisée pour décrire la thermodynamique des processus chimiques et physiques. L'enthalpie est définie comme la somme de l'énergie interne (U) d'un système et du produit mathématique de sa pression (P) et de son volume (V) :

H = U + PV

L'enthalpie est également une fonction d'état. Les valeurs d'enthalpie de substances spécifiques ne peuvent pas être mesurées directement ; seules les modifications d'enthalpie liées aux processus chimiques ou physiques peuvent être déterminées. Pour les processus qui se déroulent à pression constante (une condition courante pour de nombreux changements chimiques et physiques), la variation d'enthalpie (ΔH) est :

ΔH = ΔU + PΔV

La chaleur dégagée lorsque vous faites fonctionner un bec Bunsen est égale au changement d’enthalpie de la réaction de combustion du méthane qui a lieu, puisqu’elle se produit à la pression atmosphérique essentiellement constante. Une valeur négative d'un changement d'enthalpie, ΔH < 0, indique une réaction exothermique ; une valeur positive, ΔH > 0, indique une réaction endothermique.

Le ΔH et la variation de l'énergie libre, appelé delta G (∆G), sont liés par l'équation suivante, connue sous le nom d'équation de Gibbs Helmholtz ;

ΔG = ΔH − TΔS

Nous calculons généralement les conditions standard de pH, de température et de pression à pH 7,0 dans les systèmes biologiques, respectivement à 25 degrés Celsius et 100 kilopascals (1 bar). Notez que les conditions cellulaires varient considérablement de ces conditions standard, et donc les valeurs ∆G calculées standard pour les réactions biologiques seront différentes à l’intérieur de la cellule.

Ce texte est adapté d'Openstax, Biologie 2e, <a href="https://openstax.org/books/biology-2e/pages/6-3-the-laws-of-thermodynamics">Section 6.3: The Laws of Thermodynamics</a> et Openstax, Chimie 2e, <a href="https://openstax.org/books/chemistry-2e/pages/5-3-enthalpy">Section 5.3: Enthalpy</a>.
<body id="cke_pastebin" style="position: absolute; top: 287px; width: 1px; height: 180px; overflow: hidden; margin: 0px; padding: 0px; left: -1000px;">
et Openstax, Chimie 2e,
</body>

Enthalpie dans La Cellule

L’enthalpie (H) est utilisée pour décrire la thermodynamique des processus chimiques et physiques. L'enthalpie est définie comme la somme de l'énergie interne d'un système ...

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

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 occur at constant pressure, which is common in many chemical and physical processes, ΔH equals ΔU + PΔV.

A simple example is the heat released when a Bunsen burner burns methane. That heat is equal to the enthalpy change of the combustion reaction because the reaction happens at essentially constant atmospheric pressure. A negative ΔH means the reaction is exothermic, while a positive ΔH means it is endothermic.

Enthalpy also connects to free energy through the Gibbs-Helmholtz equation, ΔG = ΔH − TΔS. In biology, standard conditions are usually pH 7.0, 25 degrees Celsius, and 100 kilopascals, or 1 bar. Cellular conditions often differ from these standards, so standard calculated ΔG values for biological reactions can change inside the cell.

Cellular Enthalpy and Energy Changes

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 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

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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

oxidation-and-reduction-of-organic-molecules

Electron Carriers in Cell Energy Transfer

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Enzyme Function, Cofactors, and Inhibitors

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enzymes and activation energy

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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...

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Graphing Enzyme Kinetics Data

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turnover number and catalytic efficiency

How Fast Enzymes Work in Digestion

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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

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ribozymes

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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

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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

Explore enthalpy, ΔH, and Gibbs free energy in cells. Learn how constant pressure, exothermic and endothermic reactions, and cellular conditions affect energy change.

Cellular Enthalpy and Energy Changes | 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.

Enthalpy (H) is used to describe the thermodynamics of chemical and physical processes. Enthalpy is defined as the sum of a system&#39;s internal energy ...

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BIO.11.B

Science concepts--biological structures, functions, and processes. The student knows the significance of matter cycling, energy flow, and enzymes in living organisms. The student is expected to:

Cellular Enthalpy and Energy Changes

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