[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Glycolysis [Biochemistry](https://durgical.com/en/biochemistry/) · Metabolic pathway # Glycolysis Glycolysis splits one glucose into two pyruvates in the cytosol, leaving a net 2 ATP and 2 NADH; it runs with or without oxygen. Updated 2026-10-31 ## Interactive map **Balance:** ATP +2 NADH +2 pyruvate +2 ## Key facts - It happens in the cytosol of every cell; the red blood cell, which has no mitochondria, relies on it alone. - Investment phase (steps 1–5): 2 ATP spent. Payoff phase (steps 6–10): 4 ATP and 2 NADH made. Net: 2 ATP, 2 NADH, 2 pyruvate. - Three steps are irreversible and regulated: hexokinase, phosphofructokinase-1 (the committed step) and pyruvate kinase. - Without oxygen, lactate dehydrogenase turns pyruvate into lactate and regenerates the NAD⁺ glycolysis needs to keep going. - ATP is made by substrate-level phosphorylation (steps 7 and 10), with no respiratory chain. **Also called** Embden–Meyerhof pathway ## Regulation - PFK-1 is the main control: AMP and fructose 2,6-bisphosphate activate it; ATP, citrate and acidity inhibit it. - Insulin raises fructose 2,6-bisphosphate in the liver and speeds glycolysis; glucagon lowers it. - Hexokinase is slowed by its product, glucose 6-phosphate; liver glucokinase is not. - Fructose 1,6-bisphosphate activates pyruvate kinase ahead of time; ATP, alanine and (in the liver) glucagon slow it. ## The steps, one by one - **Step 1 · [Hexokinase (glucokinase in liver and pancreas)](https://durgical.com/en/biochemistry/enzymes/hexokinase/)** irreversible [Glucose](https://durgical.com/en/biochemistry/molecules/glucose/) + [ATP](https://durgical.com/en/biochemistry/molecules/atp/) → [Glucose 6-phosphate](https://durgical.com/en/biochemistry/molecules/glucose-6-phosphate/) + ADP Phosphorylates glucose at carbon 6: charged, it can no longer leave the cell. **If it fails:** Glucokinase mutations: MODY 2 (mild, stable hyperglycemia); hexokinase deficiency: a rare hemolytic anemia. [Type 2 diabetes mellitus →](https://durgical.com/en/conditions/type-2-diabetes-mellitus/) - **Step 2 · Phosphoglucose isomerase** [Glucose 6-phosphate](https://durgical.com/en/biochemistry/molecules/glucose-6-phosphate/) ⇌ fructose 6-phosphate Turns an aldose into a ketose: the six-membered ring becomes a five-membered one and C1 is free for another phosphate. **If it fails:** Glucose-6-phosphate isomerase deficiency: the second enzyme cause of non-spherocytic hemolytic anemia. - **Step 3 · [Phosphofructokinase-1 (PFK-1)](https://durgical.com/en/biochemistry/enzymes/phosphofructokinase-1/)** irreversible fructose 6-phosphate + [ATP](https://durgical.com/en/biochemistry/molecules/atp/) → [Fructose 1,6-bisphosphate](https://durgical.com/en/biochemistry/molecules/fructose-1-6-bisphosphate/) + ADP The committed, rate-limiting step: once made, fructose 1,6-bisphosphate can only go on through glycolysis. **If it fails:** Muscle PFK deficiency (Tarui disease): cramps, myoglobinuria and mild hemolysis. [Tarui disease (muscle phosphofructokinase deficiency) →](https://durgical.com/en/conditions/tarui-disease/) - **Step 4 · Aldolase** [Fructose 1,6-bisphosphate](https://durgical.com/en/biochemistry/molecules/fructose-1-6-bisphosphate/) ⇌ dihydroxyacetone phosphate + glyceraldehyde 3-phosphate Splits the six-carbon sugar into two triose phosphates (a reverse aldol reaction). **If it fails:** Aldolase B (liver): its deficiency causes hereditary fructose intolerance; aldolase A: rare myopathy and hemolysis. - **Step 5 · Triose phosphate isomerase** dihydroxyacetone phosphate ⇌ glyceraldehyde 3-phosphate Turns dihydroxyacetone phosphate into glyceraldehyde 3-phosphate: from here everything happens twice per glucose. **If it fails:** TPI deficiency: hemolytic anemia with progressive neurological disease. - **Step 6 · [Glyceraldehyde-3-phosphate dehydrogenase](https://durgical.com/en/biochemistry/enzymes/glyceraldehyde-3-phosphate-dehydrogenase/)** glyceraldehyde 3-phosphate + [NAD⁺](https://durgical.com/en/biochemistry/molecules/nad/) + phosphate (Pi) ⇌ 1,3-bisphosphoglycerate + NADH Oxidises the aldehyde and adds an inorganic phosphate: the only step that makes NADH. **If it fails:** Arsenic poisoning: arsenate uncouples this step (and arsenite blocks PDH). [Arsenic poisoning →](https://durgical.com/en/conditions/arsenic-poisoning/) - **Step 7 · Phosphoglycerate kinase** 1,3-bisphosphoglycerate + ADP ⇌ 3-phosphoglycerate + [ATP](https://durgical.com/en/biochemistry/molecules/atp/) First substrate-level phosphorylation: the high-energy phosphate goes to ADP. **If it fails:** In red cells, bisphosphoglycerate mutase diverts 1,3-BPG to 2,3-BPG (no ATP), which tunes hemoglobin. PGK1 deficiency: hemolysis, myopathy. - **Step 8 · Phosphoglycerate mutase** 3-phosphoglycerate ⇌ 2-phosphoglycerate Moves the phosphate from C3 to C2, via a phosphorylated histidine and 2,3-BPG. **If it fails:** Muscle PGAM deficiency (glycogen storage disease type X): exercise intolerance and myoglobinuria. - **Step 9 · Enolase** 2-phosphoglycerate ⇌ phosphoenolpyruvate + H₂O Removes a water molecule and makes phosphoenolpyruvate, a very high-energy compound. **If it fails:** Neuron-specific enolase (NSE) is used as a marker of small-cell lung cancer and neuroblastoma. - **Step 10 · [Pyruvate kinase](https://durgical.com/en/biochemistry/enzymes/pyruvate-kinase/)** irreversible phosphoenolpyruvate + ADP → [Pyruvate](https://durgical.com/en/biochemistry/molecules/pyruvate/) + [ATP](https://durgical.com/en/biochemistry/molecules/atp/) Second substrate-level phosphorylation; the enol becomes a ketone and the reaction cannot go back. **If it fails:** Pyruvate kinase deficiency: the most common enzyme cause of non-spherocytic hemolytic anemia. [Pyruvate kinase deficiency →](https://durgical.com/en/conditions/pyruvate-kinase-deficiency/) - **Without oxygen (LDH) · Lactate dehydrogenase (without oxygen)** [Pyruvate](https://durgical.com/en/biochemistry/molecules/pyruvate/) + NADH ⇌ [Lactate](https://durgical.com/en/biochemistry/molecules/lactate/) + [NAD⁺](https://durgical.com/en/biochemistry/molecules/nad/) Reduces pyruvate to lactate and returns NAD⁺ to step 6: that is how glycolysis keeps going without oxygen. **If it fails:** When lactate is made faster than the liver can use it, lactic acidosis follows. [Lactic acidosis →](https://durgical.com/en/conditions/lactic-acidosis/) ## Clinical notes - Defects of red-cell glycolytic enzymes cause non-spherocytic hemolytic anemia; the most common is pyruvate kinase deficiency. - Tumours burn a lot of glucose even with oxygen (Warburg effect); FDG-PET uses the fact that hexokinase traps labelled 2-deoxyglucose. - The fluoride in grey-top tubes inhibits enolase: the blood stops using glucose and the reading stays accurate. - Arsenate uncouples step 6: glycolysis goes on but leaves no net ATP. ## Related conditions - [Pyruvate kinase deficiency](https://durgical.com/en/conditions/pyruvate-kinase-deficiency/) - [Tarui disease (muscle phosphofructokinase deficiency)](https://durgical.com/en/conditions/tarui-disease/) - [Arsenic poisoning](https://durgical.com/en/conditions/arsenic-poisoning/) - [Lactic acidosis](https://durgical.com/en/conditions/lactic-acidosis/) - [Type 2 diabetes mellitus](https://durgical.com/en/conditions/type-2-diabetes-mellitus/) ## Related - [Glucose](https://durgical.com/en/biochemistry/molecules/glucose/) - [Glucose 6-phosphate](https://durgical.com/en/biochemistry/molecules/glucose-6-phosphate/) - [Fructose 1,6-bisphosphate](https://durgical.com/en/biochemistry/molecules/fructose-1-6-bisphosphate/) - [Pyruvate](https://durgical.com/en/biochemistry/molecules/pyruvate/) - [Lactate](https://durgical.com/en/biochemistry/molecules/lactate/) - [ATP (adenosine triphosphate)](https://durgical.com/en/biochemistry/molecules/atp/) - [NAD⁺ (nicotinamide adenine dinucleotide)](https://durgical.com/en/biochemistry/molecules/nad/) - [Hexokinase](https://durgical.com/en/biochemistry/enzymes/hexokinase/) - [Phosphofructokinase-1 (PFK-1)](https://durgical.com/en/biochemistry/enzymes/phosphofructokinase-1/) - [Glyceraldehyde-3-phosphate dehydrogenase (GAPDH)](https://durgical.com/en/biochemistry/enzymes/glyceraldehyde-3-phosphate-dehydrogenase/) - [Pyruvate kinase](https://durgical.com/en/biochemistry/enzymes/pyruvate-kinase/) - [Hemoglobin and 2,3-BPG](https://durgical.com/en/biochemistry/enzymes/hemoglobin-and-2-3-bpg/) - [Krebs cycle (citric acid cycle)](https://durgical.com/en/biochemistry/pathways/krebs-cycle/) - [Pyruvate dehydrogenase complex (PDH)](https://durgical.com/en/biochemistry/enzymes/pyruvate-dehydrogenase-complex/) - [Acetyl-CoA](https://durgical.com/en/biochemistry/molecules/acetyl-coa/) ## Test yourself Think of the answer, then tap the question to see it. ## What is the net yield of glycolysis per glucose? 2 ATP, 2 NADH and 2 pyruvate: 2 ATP are spent (steps 1 and 3) and 4 are made (steps 7 and 10). ## Which enzyme catalyses the committed step of glycolysis? Phosphofructokinase-1; AMP and fructose 2,6-bisphosphate activate it, ATP and citrate inhibit it. ## Why does the red blood cell need lactate dehydrogenase? It has no mitochondria: only LDH regenerates the NAD⁺ that step 6 uses up. ## What does arsenate do to glycolysis? It replaces phosphate at GAPDH; the product falls apart and the ATP of step 7 is lost, leaving no net ATP. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/biochemistry/pathways/glycolysis/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [Glycolysis](https://reactome.org/PathwayBrowser/#/R-HSA-70171) (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011); [Lactic acidosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000391.htm) (MedlinePlus, US National Library of Medicine, 2026). [← All of biochemistry](https://durgical.com/en/biochemistry/) ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/biochemistry/pathways/glycolysis/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/pathways/glycolysis/