• In cytoplasm
  • anaerobic
  • uses 2 ATP in total and produces 4: net total is 2 ATP
  • oxidation of glucose to 3-C Pyruvate
  • Regulated by hexokinase, phoshofructokinase, pruvate kinase
  • Has 3 stages: activation, cleavage and oxidation 
  • INtermediate NAD+ reduced 2x = 3 ATP made
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Glycolysis Step 1 - Activation

  • Divided into 3 steps; phosphorylation, isomerisation and 2nd phosphorylation.
  • Starting product: glucose
  • Final Product- fructose-1,6-bisphosphate
  • 1st step: phosphate added to glucose and energy from hydrolysis of Atp used - hexokinase - glucose-6-phosphate formed.
  • 2nd step: isomerisation g-6-p to fructose-6-phosphate - glucose ring opens - phosphoglucose isomerase.
  • 3rd step: second isomerisation- uses Atp and producs is fructose 1,6 - bisphosphate-  phosphofructokinase.
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Glycolysis Step 2 - Cleavage

  • The products are isomers 
  • initial cleavage forms 2 3-C sugars- dihydroxyacetone phosphate - aldolase 
  • driven by consumption of glyceraldehyde-3-phosphate- triose phosphate isomerase
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Glycolysis Step 3 - Second Phosphorylation

  • 2x of everything
  • From glyceraldehyde 3 - phosphate phosphorylaion is ocupled with oxidation and occurs via the thioester intermediate and uses amino acids at the active site of the enzyme - glyceraldehyde - 3 - phosphate dehydrogenase - forms 1,3 biphosphoglycerate. Nad+ also reduced to NADH 
  • Atp produced- formes 3-phosphoglycerate - phospho- glycerate kinase 
  • rearrangement - 2-phosphoglycerate formed - phospho-glycerate mutase
  • phosphoenolpyruvate formed - enolase
  • PYRUVATE formed - pyruvate kinase also more ATP.
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Glycolysis - Regulation


  • inhibited by glocose-6-phosphae and feedback inhibition from phosphofructokinase


  • inhibited allosterically by ATP, by drop in ph, citrate and activated allostericaly by AMP and fructose 2.6-biphosphate.

Pyruvate Kinase:

  • inhibited allosterically by ATP, alamine and by phosphorylation in live. It is activated by fructose 1,6-biphosphate.

AMP- build up of AMP means ATP is needed ,  a small increase in ATP leads to higher increase in AMP.

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Glycolysis - Fate of Pyruvate


  • fermentation, 2 steps carboxylation with enzyme pyruvate decarboxylase - forms acetaldehyde then reduction of NAD+  ( catalysis by alcohol dehydrogenase) which leads to ethanol. 


  • Important in muscles during intense actvity- lactate dehydrogenase which regenarates nad+ as NADH gets oxidised.

Acetyl Coa

  • Carier protein takes pyruvate to mitochondrial matrix and oxidative decarboxylation takes place which is irreversible and allows the citric acid cycle to begin with acetyl coa. Pyruvate dehydrogenase is used aerobic conditions. Nad+ reduced.
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Glycolysis - Pyruvate to Acetyl Coa

Pyruvate Dehydrogenase - enzyme complex - 3 cofactors: TPP, lipoic acid and FAD

Pyruvate Dehydrogenase (E1) - pyrvate combines iwth tpp (decarboxylation) andn oxidation to acetyl and transfer to lipoamide- TPP regenerated.

Dihydrolipoyl transacetylase (E2) - Transfer of acetyl group to CoA forming Acetyl Coa

Dihydrolipoyl dehydrogenase (E3) - regenaretion of lipoamide via transfer of H2 to FAD, NAD+ reduced and FAD regenerated. 

SUMMARY- 1NADH formed: 2.5 ATP

All cofactors regenerated

CO2 removed from pyruvate = Acetyl CoA

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Citric Acid Cycle:

  • Aka krebs cycle- 1937
  • Final common pathway fro all fuels 
  • 8 steps
  • In mitochondria
  • Acetyl group to 2co2
  • Forms 3NADH and 1FADH2, 1GTP (=1ATP) or 1ATP via Substrate phosphorylation.
  • Source of precursors for biosynthesis 
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Citric Acid Cycle: 1-5

  • 1: Citrate synthisis- citrate synthase , oxaloacetate (causes structural change by creating a binding site for acetyl CoA and regulates reaction - induced fit) consendensation with acetyl Coa giving citryl CoA (has high thioester bond that drives overall reaction) Then hydrolysis to Citrate and CoA.
  • 2: Isomerisation to Isocitrate: aconitase - dehydration and hydration.
  • 3- First oxidation/reduction: isocitrate dehydrogenase- 2 steps dehydrogenation and decarboxylation- oxidative decarboxylation, generates NADH and co2 and froms alpha-ketogluterate.
  • 4- Second Oxidation/reduction: alpha-ketogluterate dehydrigenase: oxidative decarboxylation forming succinyl CoA - generate NADH - comparable to formation of Actyl Coa enzyme complex has 3 co enzymes like pyruvate dehydrogenase. coa->co2
  • Susbtrate Phosphorylation- succinyl Coa Synthetase - coupled reaction- yeld 1 gtp/ATP as the phosphat egroup can be transfered to the ATP (nucleoside diphosphokinase)- Coa Formed.
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Citric Acid Cycle: 6-8

  • Rest of the steps are for the regenartion of oxaloactate 
  • 6- Oxidation: succinyl dehydrogenase- formes fumarate and reduced FAD to FADH2 (stays bound to enzyme), the enzyme forms 1 of the enzyme complexes of etc, contains ironsulphur clusters.
  • 7- Hydration: fumarase- h2o added
  • 8- Oxidation: malate dehydrogenase - yields NADH and oxaloacetate is regenarated, has a large +ve DeltaG which is riven by the consumption of oxaloacetate and NADH.
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Citric Acid Cycle: Regulation

1- Pyruvate dehydrogenase:

Between pyruvate and acetyl coa- its inhibited by products acetyl coa and nadh and also Atp. It is activated by ADP and pyruvate. Enzyme itself is reguated by phosphorylation and kinase is activated by high acetl coa, nadh and atp and inhibited by adp and pyruvate. the phosphatase is activated by Calcium and hormones.

2-Isocitrate dehydrogenase:

Activated allosterically by adp and inhibited allosterically by ATP and at the active site by NADH.

3; alpha-ketolutarate dehydrogenase-

Inhibited by succinyl coa, nadh and atp.

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Glycolysis and Citric Acid Yields

glycolysis- net yield of 2 ATP and 2NADH (=3ATP)

pyruvate to Acetyl Coa- 2NADH (=5ATP)

Citric Acid Cycle- 2x Pyruvate from 1 Glucose

6NADH (15 ATP)

2FADH2 (=3ATP)


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