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Related Concept Videos

Electron Transport Chain Components01:29

Electron Transport Chain Components

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The electron transport chain (ETC) is a crucial metabolic pathway that facilitates energy conversion in prokaryotic and eukaryotic cells. In eukaryotes, the ETC comprises four membrane-associated protein complexes in the inner mitochondrial membrane. In prokaryotes, the ETC in the plasma membrane can vary in composition, with fewer or different complexes depending on the organism and environmental conditions. These complexes transfer electrons from electron donors, such as NADH and FADH2, to...
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ATP Synthase: Mechanism01:48

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In animals, the mitochondrial F1F0 ATP synthase is the key protein that synthesizes ATP molecules through a complex catalytic mechanism. While the nuclear genome encodes the majority of ATP synthase subunits, the mitochondrial genome encodes some of the enzyme's most critical components. The formation of this multi-subunit enzyme is a complex multi-step process regulated at the level of transcription, translation, and assembly. Defects in one or more of these steps can result in decreased...
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ATP Synthase: Structure01:18

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ATP synthase or ATPase is among the most conserved proteins found in bacteria, mammals, and plants. This enzyme can catalyze a forward reaction in response to the electrochemical gradient, producing ATP from ADP and inorganic phosphate. ATP synthase can also work in a reverse direction by hydrolyzing ATP and generating an electrochemical gradient. Different forms of ATP synthases have evolved special features to meet the specific demands of the cell. Based on their specific feature, ATP...
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Electron Transport Chains01:28

Electron Transport Chains

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The final stage of cellular respiration is oxidative phosphorylation that consists of two steps: the electron transport chain and chemiosmosis. The electron transport chain is a set of proteins found in the inner mitochondrial membrane in eukaryotic cells. Its primary function is to establish a proton gradient that can be used during chemiosmosis to produce ATP and generate electron carriers, such as NAD+ and FAD, that are used in glycolysis and the citric acid cycle.
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Electron Transport Chain: Complex III and IV01:43

Electron Transport Chain: Complex III and IV

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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...
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Electron Transport Chain: Complex I and II01:46

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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.
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Visualizing the protons in a metalloenzyme electron proton transfer pathway.

Hanna Kwon1, Jaswir Basran2,3, Juliette M Devos4

  • 1School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom.

Proceedings of the National Academy of Sciences of the United States of America
|March 11, 2020
PubMed
Summary

This study reveals precise proton locations in ascorbate peroxidase using neutron crystallography. This advances understanding of proton-coupled electron transfer in biological redox reactions.

Keywords:
ascorbatehemeneutronperoxidaseproton transfer

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Enzymology

Background:

  • Proton-coupled electron transfer (PCET) is crucial for biological redox processes like respiration and photosynthesis.
  • Understanding PCET mechanisms requires detailed knowledge of proton pathways and hydrogen bonding within metalloenzymes.
  • Proton delivery mechanisms in metalloenzymes remain incompletely understood.

Purpose of the Study:

  • To elucidate the protonation states and hydrogen bonding structures within a metalloenzyme's proton pathway.
  • To provide direct structural insights into proton movement during redox catalysis.

Main Methods:

  • Neutron crystallography was employed to determine the 2.1-Å structure of the ascorbate peroxidase-ascorbate complex.
  • Direct observation of protonation states of the substrate and enzyme residues involved in electron/proton transfer.

Main Results:

  • The neutron crystal structure directly revealed the protonation states of ascorbate and key residues in the transfer pathway.
  • Detailed hydrogen bonding networks and proton locations were identified within the enzyme-substrate complex.

Conclusions:

  • The findings offer direct structural evidence for proton movements during heme-catalyzed oxygen activation.
  • This work illuminates the mechanism of ascorbate oxidation and provides a foundation for studying other PCET processes.