aerobic metabolism
- Krebs cycle
- Electron Transport Chain
- Electron Shuttle System
Krebs cycle
Krebs cycle start with the oxidation of pyruvate. Pyruvate that is produced by glycolysis will enter the mitochondria when there is sufficient oxygen. This process is catalysed by the enzyme pyruvate dehydrogenase and will produce acetyl coA, NADH and carbon dioxide. Acetyl coA will then enter the Krebs cycle.
- Upon entering the Krebs cycle, acetyl coA (2C) will enter oxaloacetate (4C) to form citrate (6C). The enzyme catalysing this reaction is citrate synthetase enzyme. Citric acid rearranges itself to become isometric acid. Aconitase enzyme catalyses this reaction
- Oxidative decarboxylation of isocitric acid (6C) produces α-ketoglutarate (5C). Carbon dioxide and NADH is produced during this reaction.
- Oxidative decarboxylation of α-ketoglurate (5C) will produce succinic acid (4C). Carbon dioxide and NADH is formed during this reaction. GTP is also produced. This GTP is then hydrolysed into GDP. This hydrolysis reaction produces energy that is used for phosphorylation of ADP to ATP.
- Succinic acid is then oxidised to fumarate. This reaction is catalysed by the succinate dehydrogenase. FADH2 is formed in this oxidation.
- Fumarate is hydrated to become malic acid. This reaction is catalysed by fumarase.
- Malic acid is then oxidised to produce oxaloacetate again, catalysed by malate dehydrogenase. NADH is produced.
electron transport chain
Electron transport system is a series of electron carrier and hydrogen carriers embedded in the inner membrane of the mitochondrion.
- In the initial step, NADH transfers hydrogen atom to flavoprotein, the first carrier of the system. Flavoprotein accepts the hydrogen and is reduced to reduces flavoprotein.
- Reduced flavoprotein then transfers the hydrogen atoms to coenzyme Q. Coenzyme accepts the hydrogen atoms and becomes reduced coenzyme Q.
- After coenzyme Q, both hydrogen atoms spilt into 2 protons (H+) and a pair of electrons. This pair of electrons is then transferred through a series of electron carries which are at progressively low energy level. Electrons are first transferred to cytochrome b, which become reduced cytochrome b. Reduced cytochrome b then transfer 2 electrons to cytochrome C which become reduced cytochrome C. Reduced cytochrome C finally transfer its electron to cytochrome aa3.
- Reduced cytochrom aa3 then transfers electrons t oxygen. Oxygen then combines with hydrogen ions to form water. In the final set of aerobic respiration, oxygen is reduced to water.
- The transfer of electrons along the electron carrie, causes protons (H+) to be pumped from the matrix to the inter membrane space of the mitochondrion. This process establishes an electrochemical gradient across the inner membrane of the mitochondrion. Protons then move along this gradient from the inter membrane space to the matrix through a channel protein ATP synthetase. As this occurs, energy is realised. This energy is used by ATP synthetase for the phosphorylation of ADP to ATP.
electron shuttle system
NADH generated outside the mitochondria cannot be transported through he inner membrane. Therefore, cytoplasmic NADH must be recycled by Electron Shuttle System. This system carries electron through the membrane in the form of educed substrates.
- Malate-Aspartate Shuttle
- Glycerol-3-Phosphate Shuttle
Malate Aspartate Shuttle
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Glycerol-3-Phosphate Shuttle
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