Electron Transport Chain https://en.wikipedia.org/wiki/Electron_transport_chain

In Complex I (NADH reductase or NADH dehydrogenase), two electrons are removed from NADH and ultimately transferred to a lipid-soluble carrier, ubiquinone (UQ). The reduced product, ubiquinol (UQH2), freely diffuses within the membrane, and Complex I translocates four protons (H+) across the membrane, thus producing a proton gradient. Complex I is one of the main sites at which premature electron leakage to oxygen occurs, thus being one of the main sites of production of superoxide. This complex is inhibited by Alkylguanides (Example: Guanethidine), Rotenone, Barbiturates, Chlorpromazine, Piericidin. In Complex II (succinate dehydrogenase or fumarate reductase) additional electrons are delivered into the quinone pool (Q) originating from succinate and transferred (via flavin adenine dinucleotide (FAD)) to Q. Complex II consists of four protein subunits: succinate dehydrogenase, (SDHA); succinate dehydrogenase [ubiquinone] iron-sulfur subunit, mitochondrial, (SDHB); succinate dehydrogenase complex subunit C, (SDHC) and succinate dehydrogenase complex, subunit D, (SDHD). Other electron donors (e.g., fatty acids and glycerol 3-phosphate) also direct electrons into Q (via FAD). Complex 2 is a parallel electron transport pathway to complex 1, but unlike complex 1, no protons are transported to the intermembrane space in this pathway. Therefore, the pathway through complex 2 contributes less energy to the overall electron transport chain process. This complex is inhibited by Carboxin In Complex III (cytochrome bc1 complex or cytochrome c reductase), the Q-cycle contributes to the proton gradient by an asymmetric absorption/release of protons. Two electrons are removed from QH2 at the QO site and sequentially transferred to two molecules of cytochrome c, a water-soluble electron carrier located within the intermembrane space. The two other electrons sequentially pass across the protein to the Qi site where the quinone part of ubiquinone is reduced to quinol. A proton gradient is formed by one quinol (oxidations at the Qo site to form one quinone () at the Qi site. (In total, four protons are translocated: two protons reduce quinone to quinol and two protons are released from two ubiquinol molecules.) QH2 + 2 cytochrome c(FeIII) + 2H+

in à Q + 2 cytochrome c(FeII) + 4H+out

When electron transfer is reduced (by a high membrane potential or respiratory inhibitors such as antimycin A), Complex III may leak electrons to molecular oxygen, resulting in superoxide formation. This complex is inhibited by dimercaprol (British Antilewisite, BAL), Napthoquinone and Antimycin.

In Complex IV (cytochrome c oxidase), four electrons are removed from four molecules of cytochrome c and transferred to molecular oxygen (O2), producing two molecules of water. At the same time, eight protons are removed from the mitochondrial matrix (although only four are translocated across the membrane), contributing to the proton gradient. The activity of cytochrome c oxidase is inhibited by cyanide, carbon monoxide, azide, and hydrogen sulphide(H2S).

Pyruvate is Produced by Glycolysis

http://www.chemistry.wustl.edu/~edudev/LabTutorials/Cytochromes/cytochromes.html

Glucose --> 2 Pyruvate + 2 NADH + 2 ATP

NADH/NAD+ Redox

Complex II and the TCA Cycle

https://www.sciencedirect.com/science/article/pii/S2213231713000992

Notes:

1. In Complex II, the pyruvate dehydrogenase complex (PDH) converts pyruvate produced

by glycolysis and NAD+ into acetyl-CoA, NADH, and CO2. 2. Acetyl-CoA enters the TCA cycle. 3. Succinate a product of the TCA cycle is converted to fumarate by Complex II (succinate

dehydrogenase or fumarate reductase).

Creatine Kinase Shuttle https://en.wikipedia.org/wiki/Creatine_phosphate_shuttle

The creatine phosphate shuttle is an intracellular energy shuttle which facilitates transport of high energy phosphate from muscle cell mitochondria to myofibrils. In mitochondria, ATP levels are very high as a result of glycolysis, TCA cycle, oxidative phosphorylation processes, whereas creatine phosphate levels are low. This makes conversion of creatine to phosphocreatine a highly favored reaction. Phosphocreatine is a very-high-energy compound. It then diffuses from mitochondria to myofibrils. In myofibrils, during exercise (contraction) ADP levels are very high, which favors resynthesis of ATP. Thus, phosphocreatine breaks down to creatine, giving its inorganic phosphate for ATP formation. This is done by the enzyme creatine phosphokinase which transduces energy from the transport molecule of phosphocreatine to the useful molecule for contraction demands, ATP, an action performed by ATPase in the myofibril. The resulting creatine product acts as a signal molecule indicating myofibril contraction and diffuses in the opposite direction of phosphocreatine, back towards the mitochondrial intermembrane space where it can be rephosphorylated by creatine phosphokinase.

https://www.researchgate.net/figure/Phosphocreatine-shuttle-system-Adapted-from-Neubauer-S-Influence-of-left_fig1_261609410

F0F1ATPase or the ATP Synthase of Mitochondria

https://www.sciencedirect.com/topics/medicine-and-dentistry/inner-mitochondrial-membrane

http://thebiologyprimer.com/steps-of-cellular-respiration

“ATP consists of adenosine and three phosphate groups (triphosphate). ATP is an unstable molecule in water, in which it hydrolyses to ADP and phosphate. This is because the strength of the bonds between the phosphate groups in ATP are less than the strength of the hydrogen bonds, between its products (ADP + phosphate), and water. Thus, if ATP and ADP are in chemical equilibrium in water, almost all of the ATP will eventually be converted to ADP. A system that is far from equilibrium is capable

of doing work. Living cells maintain the ratio of ATP to ADP at a point ten orders of magnitude from equilibrium, with ATP concentrations a thousand-fold higher than the concentration of ADP. This displacement from equilibrium means that the

hydrolysis of ATP in the cell releases a large amount of free energy.”

https://www.sciencedirect.com/topics/medicine-and-dentistry/inner-mitochondrial-membrane

“Electron transport chain ROS generation by mitochondria and dissipation of the proton gradient by UCPs. Scavenging by antioxidant defenses is insufficient to prevent oxidative stress.”