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Electron Transport Chain: Complex I and II

Electron Transport Chain: Complex I and II

The mitochondrial electron transport chain (ETC) is the main energy generation system in the eukaryotic cells. However, mitochondria also produce cytotoxic reactive oxygen species (ROS) due to the large electron flow during oxidative phosphorylation. While Complex I is one of the primary sources of superoxide radicals, ROS production by Complex II is uncommon and may only be observed in cancer cells with mutated complexes.
ROS generation is regulated and maintained at moderate levels necessary...

Cofactors and Coenzymes

Cofactors and Coenzymes

Enzymes are proteins made of amino acids. The functional group of each constituent amino acid catalyzes a wide variety of chemical reactions via ionic interactions or acid-base reactions. However, amino acids cannot catalyze oxidation-reduction and group transfer reactions and need to be aided by non-protein components called cofactors. Cofactors are also referred to as the chemical teeth of an enzyme.
Cofactors can be metallic ions or organic molecules called coenzymes. These types of helper...

Cofactors and Coenzymes

Cofactors and Coenzymes

Enzymes require additional components for proper function. There are two such classes of molecules: cofactors and coenzymes. Cofactors are metallic ions and coenzymes are non-protein organic molecules. Both of these types of helper molecule can be tightly bound to the enzyme or bound only when the substrate binds.

Cofactors and Coenzymes

Cofactors and Coenzymes

Enzymes require additional components for proper function. There are two such classes of molecules: cofactors and coenzymes. Cofactors are metallic ions and coenzymes are non-protein organic molecules. Both of these types of helper molecule can be tightly bound to the enzyme or bound only when the substrate binds.

Electron Transport Chain: Complex III and IV

Electron Transport Chain: Complex III and IV

During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...

Role of Reduced Coenzymes NADH and FADH₂

Role of Reduced Coenzymes NADH and FADH₂

The energy released from the breakdown of the chemical bonds within nutrients can be stored either through the reduction of electron carriers or in the bonds of adenosine triphosphate (ATP). In living systems, a small class of compounds functions as mobile electron carriers, molecules that bind to and shuttle high-energy electrons between compounds in pathways. The principal electron carriers that will be considered originate from the B vitamin group and are derivatives of nucleotides; they are...

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Related Experiment Video

Updated: Jun 27, 2026

Inner Mitochondrial Membrane Sensitivity to Na+ Reveals Partially Segmented Functional CoQ Pools

Inner Mitochondrial Membrane Sensitivity to Na⁺ Reveals Partially Segmented Functional CoQ Pools

Published on: July 20, 2022

The evolution of coenzyme Q.

Frederick L Crane¹

¹Department of Biological Science, Purdue University, West Lafayette, IN, USA. flccoq10@aol.com

Biofactors (Oxford, England)

|December 20, 2008

Summary

This summary is machine-generated.

Coenzyme Q, initially found as an electron carrier, performs diverse cellular roles including antioxidant and proton transfer functions. Ongoing research continues to uncover its therapeutic potential and complex cellular mechanisms.

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Quantification of Coenzyme A in Cells and Tissues

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Last Updated: Jun 27, 2026

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Assessment of Open Probability of the Mitochondrial Permeability Transition Pore in the Setting of Coenzyme Q Excess

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Quantification of Coenzyme A in Cells and Tissues

Quantification of Coenzyme A in Cells and Tissues

Published on: September 27, 2019

Area of Science:

Biochemistry
Cell Biology
Mitochondrial Function

Background:

Coenzyme Q was identified as a crucial mitochondrial electron carrier.
Its discovery followed earlier work on flavins and cytochromes.
Research in D.E. Green's lab identified coenzyme Q's role in electron transport between dehydrogenases and cytochromes.

Purpose of the Study:

To explore the diverse and unexpected functions of coenzyme Q in cellular processes.
To investigate the roles of coenzyme Q beyond its initial identification as an electron carrier.
To understand the basis for coenzyme Q deficiency and its therapeutic applications.

Main Methods:

Investigated membrane lipids to identify coenzyme Q.
Studied transmembrane proton transfer in relation to ATP synthesis.
Examined the distribution and functions of coenzyme Q in various cellular compartments.

Main Results:

Coenzyme Q functions as a primary antioxidant.
It plays a role in the acidification of Golgi and lysosomal vesicles.
Evidence suggests roles in proton release, H2O2 generation, and apoptosis prevention.

Conclusions:

Coenzyme Q has multifaceted cellular functions, including antioxidant and signaling roles.
Identification of coenzyme Q synthesis genes aids in defining deficiency.
Further research is needed to fully elucidate its effects on membrane structure and therapeutic actions.