1. Glycolysis (Cytoplasm):
* Hexokinase: Phosphorylates glucose, trapping it within the cell and preparing it for further breakdown.
* Phosphoglucose isomerase: Converts glucose-6-phosphate to fructose-6-phosphate.
* Phosphofructokinase-1 (PFK-1): The key regulatory enzyme of glycolysis. It phosphorylates fructose-6-phosphate to fructose-1,6-bisphosphate, committing the molecule to glycolysis.
* Aldolase: Cleaves fructose-1,6-bisphosphate into two 3-carbon molecules, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
* Triose phosphate isomerase: Converts dihydroxyacetone phosphate to glyceraldehyde-3-phosphate.
* Glyceraldehyde 3-phosphate dehydrogenase: Oxidizes glyceraldehyde-3-phosphate and adds a phosphate group, producing 1,3-bisphosphoglycerate.
* Phosphoglycerate kinase: Transfers a phosphate group from 1,3-bisphosphoglycerate to ADP, producing ATP.
* Phosphoglycerate mutase: Rearranges the phosphate group on 3-phosphoglycerate, creating 2-phosphoglycerate.
* Enolase: Dehydrates 2-phosphoglycerate, producing phosphoenolpyruvate (PEP).
* Pyruvate kinase: Transfers a phosphate group from PEP to ADP, producing ATP and pyruvate.
2. Pyruvate Oxidation (Mitochondrial Matrix):
* Pyruvate dehydrogenase complex: A multi-enzyme complex that converts pyruvate into acetyl-CoA, releasing carbon dioxide and reducing NAD+ to NADH.
3. Citric Acid Cycle (Mitochondrial Matrix):
* Citrate synthase: Condenses acetyl-CoA with oxaloacetate to form citrate.
* Aconitase: Isomerizes citrate to isocitrate.
* Isocitrate dehydrogenase: Oxidizes isocitrate to α-ketoglutarate, producing CO2 and reducing NAD+ to NADH.
* α-ketoglutarate dehydrogenase complex: Oxidizes α-ketoglutarate to succinyl-CoA, producing CO2 and reducing NAD+ to NADH.
* Succinyl-CoA synthetase: Converts succinyl-CoA to succinate, generating GTP (which is later converted to ATP).
* Succinate dehydrogenase: Oxidizes succinate to fumarate, reducing FAD to FADH2.
* Fumarase: Hydrates fumarate to malate.
* Malate dehydrogenase: Oxidizes malate to oxaloacetate, reducing NAD+ to NADH.
4. Oxidative Phosphorylation (Inner Mitochondrial Membrane):
* Electron transport chain: A series of protein complexes that transfer electrons from NADH and FADH2 to oxygen, releasing energy that drives the pumping of protons across the inner mitochondrial membrane.
* ATP synthase: Uses the proton gradient created by the electron transport chain to synthesize ATP from ADP and phosphate.
In summary, enzymes play an essential role in every step of cellular respiration, ensuring the efficient and controlled breakdown of glucose and the production of ATP. Their specific catalytic activities allow for the conversion of molecules, the release of energy, and the generation of electron carriers that fuel the final ATP production.
