3.10:

3.10: Oxydation et réduction des molécules organiques

Oxidation and Reduction of Organic Molecules

JoVE Core
Cell Biology

A subscription to JoVE is required to view this content. Sign in or start your free trial.

JoVE Core Cell Biology

Oxidation and Reduction of Organic Molecules

3.6: Endergonic and Exergonic Reactions in the Cell

3.11: Introduction to Enzymes

6,680 Views

•

01:19 min

•

April 30, 2023

Overview

Energy production within a cell involves many coordinated chemical pathways. Most of these pathways are combinations of oxidation and reduction reactions, which occur at the same time. An oxidation reaction strips an electron from an atom in a compound, and the addition of this electron to another compound is a reduction reaction. Because oxidation and reduction usually occur together, these pairs of reactions are called redox reactions.

The removal of an electron from a molecule, results in a decrease in potential energy in the oxidized compound. However, the electron (sometimes as part of a hydrogen atom) does not remain unbonded in the cytoplasm of a cell. Rather, the electron is shifted to a second compound, reducing the second compound. The shift of an electron from one compound to another removes some potential energy from the first compound (the oxidized compound) and increases the potential energy of the second compound (the reduced compound). The transfer of electrons between molecules is important because most of the energy stored in atoms and used to fuel cell functions is in the form of high-energy electrons. The transfer of energy in the form of high-energy electrons allows the cell to transfer and use energy in an incremental fashion—in small packages rather than in a single, destructive burst.

In living systems, a small class of compounds functions as electron shuttles: they bind and carry high-energy electrons between compounds in biochemical pathways. The principal electron carriers we will consider are derived from the B vitamin group and are derivatives of nucleotides. These compounds can be easily reduced (that is, they accept electrons) or oxidized (they lose electrons). Nicotinamide adenine dinucleotide (NAD) is derived from vitamin B3, niacin. NAD⁺ is the oxidized form of the molecule; NADH is the reduced form of the molecule after it has accepted two electrons and a proton (which together are the equivalent of a hydrogen atom with an extra electron).

This text is adapted from Openstax, Biology 2e, Section 7.1 Energy in Living Systems

Transcript

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.

Key Terms and definitions

Learning Objectives

Questions that this video will help you answer

This video is also useful for

Tags

Oxydation réduction réactions d’oxydoréduction transfert d’électrons production d’énergie NAD NADH oxydé réduit transporteurs d’électrons voies biochimiques