Glycolysis
links: reference: https://www.youtube.com/watch?v=SUPQVg1vO0Q 4-11-2021
Glycolysis #
Glycolysis takes place in the Cytosol, while the citric acid cycle, which glycolysis sorta the first step of, occurs in the mitochondria.
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During anaerobic glycolysis (AKA erobic glycolysis) the pyruvate is ultimately fermented into Lactate (NOT lactic acid).
- Mitochondrial respiration is 93% more efficient than fermentation as far as energy is concerned, mainly due to CO2.
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Glucose + 2 NAD + 2 ATP + 2 Phosphate $\ce{->}$ 2 Pyruvate + 2 NADH + 2 $\ce{H+}$ + 4 ATP + 2 H2O
- Net reaction for respiration: $\ce{C6H12O6 + 6O2 -> 6CO2 + 6H2O + ATP}$
All steps except 2, 4, and 5 use Mg++ as a cofactor.
- Glucose is phosphorylized via Hexokinase into Glucose 6-Phosphate. Consumes 1 ATP.
- Glucose 6-Phosphate is reconfigured via phosphoglucoisomerase into fructose 6-phosphate.
- Fructose 6-phosphate is phosphorylized via phosphofructokinase 1 into Fructose 1,6-bisphosphase Consumes 1 ATP.
- Cleavage: Fructose 1,6-bisphosphase is split via fructose bisphosphate aldolase into Glyceraldehyde 3-Phosphate (GADP/G3P) AND Dihydroxyacetone Phosphate (DHAP).
- Dihydroxyacetone Phosphate (DHAP) is converted via triosephosphate isomerase into Glyceraldehyde 3-Phosphate (GADP/G3P), leaving us with 2 GADP. So, the following steps happen twice in one full sequence.
- Glucose + 2 ATP $\ce{->}$ 2 GADP
- Oxidation: GADP is converted via glyceraldehyde 3-phosphate dehydrogenase into [1,3-bisphosphoglycerate]. Requires 1 Pi and converts NAD+ into NADH + H+.
- This part is where the magic happens. A phosphate bond is formed without an ATP-utilizing kinase like the other steps. Was all this buildup just to make the most opportunistic molecule ever that only needs NAD+? How’s it even doing that? Is there some kind of ‘buildup’ of anabolism from the ATP that eventually allows that bond to be formed, perhaps simply thanks to environmental conditions, i.e. high presence of oxygen, in the same way one is thankful for sunlight for creating glucose?
- The reaction is two-step: oxidation and phosphorylation. Overall ΔG=6.3 kJ/mol. Oxidation is ΔG=-50kJ/mol, phosphorylation is ΔG=+50kJ/mol (highly endergonic, requires energy into system). GAPDH uses covalent catalysis and general base catalysis to decrease the very large activation energy of the second step (phosphorylation) of this reaction.
- This part is where the magic happens. A phosphate bond is formed without an ATP-utilizing kinase like the other steps. Was all this buildup just to make the most opportunistic molecule ever that only needs NAD+? How’s it even doing that? Is there some kind of ‘buildup’ of anabolism from the ATP that eventually allows that bond to be formed, perhaps simply thanks to environmental conditions, i.e. high presence of oxygen, in the same way one is thankful for sunlight for creating glucose?
- 1,3-bisphosphoglycerate is dephosphorylated via phosphoglycerate kinase into [3-phosphoglycerate]. Produces 1 ATP, out of the ADP made in steps 1/3.
- Phosphate Transfer: [3-phosphoglycerate] is converted via phosphoglycerate mutase into [2-phosphoglycerate].
- Dehydration: [2-phosphoglycerate] is converted via enolase into [Phosphoenolpyruvate]
- [Phosphoenolpyruvate] is dephosphorylated via Pyruvate Kinase into the almighty Pyruvate, and Produces 1 ATP (costing 1 ADP, synthesized in steps 1/3)
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2 GADP $\ce{->}$ 2 Pyruvate + 4 ATP.
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From here, pyruvate either enters the Pyruvate Dehydrogenase complex in the mitochondria via something like MPC2, before it enters the Citric Acid Cycle, or it is converted into Lactate via Lactate Dehydrogenase.