Electron carriers and the mitochondrial electron transport chain are crucial for cellular energy production. These molecules and protein complexes work together to transfer electrons, creating a proton gradient that powers ATP synthesis.
ATP synthesis, driven by the electron transport chain, is the primary source of cellular energy. This process is not only vital in mitochondria but also plays a role in other cellular processes like photosynthesis, bacterial energy production, and various metabolic pathways.
Electron Carriers and Mitochondrial Electron Transport Chain
Structure and function of electron carriers
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Electron carriers accept and donate electrons in redox reactions transferring electrons between components of electron transport chains
Nicotinamide adenine dinucleotide (NAD+/) consists of two nucleotides joined by phosphate groups carrying two electrons and one proton
Flavin adenine dinucleotide (FAD/) contains riboflavin attached to an ADP molecule carrying two electrons and two
Coenzyme Q (ubiquinone) lipid-soluble benzoquinone with long isoprenoid tail shuttles electrons between complexes in mitochondrial membrane
Cytochromes heme-containing proteins transfer single electrons through changes in iron oxidation state
Organization of mitochondrial electron transport
houses electron transport chain components
(NADH dehydrogenase) accepts electrons from NADH transferring to coenzyme Q
(Succinate dehydrogenase) accepts electrons from FADH2 transferring to coenzyme Q
(Cytochrome bc1 complex) accepts electrons from reduced coenzyme Q transferring to
(Cytochrome c oxidase) accepts electrons from cytochrome c transferring to molecular oxygen forming water
Electrons move from complexes with lower to higher reduction potentials releasing energy used to pump protons into intermembrane space
ATP Synthesis and Other Cellular Processes
Coupling of electron transport to ATP synthesis
Chemiosmosis drives ATP synthesis using electrochemical gradient
Proton gradient forms as Complexes I, III, and IV pump protons into intermembrane space creating electrochemical gradient across inner mitochondrial membrane
(Complex V) consists of F0 and F1 subunits catalyzing ATP synthesis using energy from proton flow
ATP synthesis mechanism:
Protons flow through ATP synthase from intermembrane space to matrix
Proton flow energy drives F0 subunit rotation
F0 rotation causes F1 conformational changes leading to ATP synthesis
ATP yield approximately 2.5 ATP molecules per NADH and 1.5 ATP molecules per FADH2
Electron transport chains in cellular processes
Photosynthesis light-dependent reactions involve electron transport chains in thylakoid membranes generating proton gradient for ATP synthesis (chloroplasts)
Bacteria and archaea use diverse electron transport chains for various energy sources with alternative terminal electron acceptors (nitrate, sulfate)
Plasma membrane electron transport present in various cell types functions in redox homeostasis and cell signaling (red blood cells)
Endoplasmic reticulum electron transport involved in protein folding and lipid metabolism including cytochrome P450 systems for detoxification and hormone synthesis (liver cells)
Nitrogen fixation electron transport chains in nitrogen-fixing bacteria provide energy for N2 reduction (Rhizobium)