exergonic reaction

Examples of exergonic reaction in the following topics:

• Activation Energy

  • Activation energy must be considered when analyzing both endergonic and exergonic reactions.
  • Exergonic reactions have a net release of energy, but they still require a small amount of energy input before they can proceed with their energy-releasing steps.
  • Cells will at times couple an exergonic reaction $(\Delta G<0)$ with endergonic reactions $(\Delta G>0)$, allowing them to proceed.
  • The free energy released from the exergonic reaction is absorbed by the endergonic reaction.
  • Although the image above discusses the concept of activation energy within the context of the exergonic forward reaction, the same principles apply to the reverse reaction, which must be endergonic.

• Free Energy

  • Reactions that have a negative ∆G and, consequently, release free energy, are called exergonic reactions.
  • Exergonic means energy is exiting the system.
  • On the other hand, the catabolic process of breaking sugar down into simpler molecules releases energy in a series of exergonic reactions.
  • Exergonic and endergonic reactions result in changes in Gibbs free energy.
  • Exergonic reactions release energy; endergonic reactions require energy to proceed.

• ATP: Adenosine Triphosphate

  • Cells couple the exergonic reaction of ATP hydrolysis with endergonic reactions to harness the energy within the bonds of ATP.
  • ATP provides the energy for both energy-consuming endergonic reactions and energy-releasing exergonic reactions, which require a small input of activation energy.
  • Cells couple the exergonic reaction of ATP hydrolysis with the endergonic reactions of cellular processes.
  • In this example, the exergonic reaction of ATP hydrolysis is coupled with the endergonic reaction of converting glucose for use in the metabolic pathway.
  • Sodium-potassium pumps use the energy derived from exergonic ATP hydrolysis to pump sodium and potassium ions across the cell membrane.

• The Second Law of Thermodynamics

  • Likewise, some energy is lost in the form of heat during cellular metabolic reactions.
  • Entropy changes also occur in chemical reactions.
  • In an exergonic chemical reaction where energy is released, entropy increases because the final products have less energy inside them holding their chemical bonds together.
  • As living systems take in energy-storing molecules and transform them through chemical reactions, they lose some amount of usable energy in the process because no reaction is completely efficient.

• Citric Acid Cycle

  • The citric acid cycle is a series of reactions that produces two carbon dioxide molecules, one GTP/ATP, and reduced forms of NADH and FADH2.
  • The eight steps of the cycle are a series of redox, dehydration, hydration, and decarboxylation reactions that produce two carbon dioxide molecules, one GTP/ATP, and reduced forms of NADH and FADH2 .
  • This step is irreversible because it is highly exergonic.
  • The rate of this reaction is controlled by negative feedback and the amount of ATP available.
  • If ATP levels increase, the rate of this reaction decreases.

• ATP in Metabolism

  • In this way, ATP is a direct link between the limited set of exergonic pathways of glucose catabolism and the multitude of endergonic pathways that power living cells.
  • The energy from ATP can also be used to drive chemical reactions by coupling ATP hydrolysis with another reaction process in an enzyme.
  • During an endergonic chemical reaction, ATP forms an intermediate complex with the substrate and enzyme in the reaction.
  • This is illustrated by the following generic reaction:
  • In phosphorylation reactions, the gamma phosphate of ATP is attached to a protein.

• The Two Parts of Photosynthesis

  • Light-dependent and light-independent reactions are two successive reactions that occur during photosynthesis.
  • Just as the name implies, light-dependent reactions require sunlight.
  • Photosystems consist of a light-harvesting complex and a reaction center.
  • In the light-independent reactions or Calvin cycle, the energized electrons from the light-dependent reactions provide the energy to form carbohydrates from carbon dioxide molecules.
  • Photosynthesis takes place in two stages: light-dependent reactions and the Calvin cycle (light-independent reactions).

• Hydrolysis

  • During these reactions, the polymer is broken into two components.
  • These reactions are in contrast to dehydration synthesis (also known as condensation) reactions.
  • Dehydration and hydrolysis reactions are chemical reactions that are catalyzed, or "sped up," by specific enzymes; dehydration reactions involve the formation of new bonds, requiring energy, while hydrolysis reactions break bonds and release energy.
  • This is the reverse of the dehydration synthesis reaction joining these two monomers.
  • This is the reverse of the dehydration synthesis reaction joining these two monomers.

• Enzyme Active Site and Substrate Specificity

  • In some reactions, a single-reactant substrate is broken down into multiple products.
  • Two reactants might also enter a reaction, both become modified, and leave the reaction as two products.
  • This dynamic binding maximizes the enzyme's ability to catalyze its reaction.
  • The enzyme will always return to its original state at the completion of the reaction.
  • After an enzyme is done catalyzing a reaction, it releases its products (substrates).

• Chemical Reactions and Molecules

  • The equations that describe these reactions contain a unidirectional arrow and are irreversible.
  • Reversible reactions are those that can go in either direction.
  • In biological reactions, however, equilibrium is rarely obtained because the concentrations of the reactants or products or both are constantly changing, often with a product of one reaction being a reactant for another.
  • These reactions are important for maintaining the homeostasis of our blood.
  • Explore reactions in which chemical bonds are formed and broken with this model.