Glycolysis – Quick Reference (EMP Pathway)

Overview

  • Glycolysis is the first metabolic step of carbohydrates where glucose is converted to pyruvate (and lactate under anaerobic conditions) with ATP production.
  • Pathway name: EMP (Embden-Meyerhof-Parnas); universal glycolytic pathway.
  • Location: cytosol; anaerobic.
  • Key outputs: ATP (net), NADH, pyruvate.

Key facts

  • Site: cytosol
  • Oxygen requirement: anaerobic
  • Net energy yield (per glucose): ATP and NADH produced during the pathway

Step-by-step overview

Step 1: Hexokinase

  • Substrate: Glucose
  • Enzyme: Hexokinase (glucokinase in liver)
  • Reaction: Glucose+ATP→Glucose-6-phosphate+ADP\text{Glucose} + \text{ATP} \rightarrow \text{Glucose-6-phosphate} + \text{ADP}
  • Note: ATP consumed

Step 2: Phosphohexose isomerase

  • Substrate: Glucose-6-phosphate
  • Product: Fructose-6-phosphate
  • Enzyme: Phosphohexose isomerase
  • Reaction: Glucose-6-phosphate⇌Fructose-6-phosphate\text{Glucose-6-phosphate} \rightleftharpoons \text{Fructose-6-phosphate}

Step 3: Phosphofructokinase-1 (PFK-1)

  • Substrate: Fructose-6-phosphate + ATP
  • Product: Fructose-1,6-bisphosphate + ADP
  • Enzyme: Phosphofructo-kinase-1
  • Reaction: Fructose-6-phosphate+ATP→Fructose-1,6-bisphosphate+ADP\text{Fructose-6-phosphate} + \text{ATP} \rightarrow \text{Fructose-1,6-bisphosphate} + \text{ADP}
  • Note: Irreversible, rate-limiting

Step 4: Aldolase

  • Substrate: Fructose-1,6-bisphosphate
  • Products: Glyceraldehyde-3-phosphate (G3P) + Dihydroxyacetone phosphate (DHAP)
  • Enzyme: Aldolase
  • Reaction: Fructose-1,6-bisphosphate→G3P+DHAP\text{Fructose-1,6-bisphosphate} \rightarrow \text{G3P} + \text{DHAP}

Step 5: Triose phosphate isomerase

  • Substrate: DHAP
  • Interconversion: DHAP ⇌ G3P
  • Note: Only G3P proceeds in subsequent steps
  • Reaction: Dihydroxyacetone phosphate⇌Glyceraldehyde-3-phosphate\text{Dihydroxyacetone phosphate} \rightleftharpoons \text{Glyceraldehyde-3-phosphate}

Step 6: Glyceraldehyde-3-phosphate dehydrogenase

  • Substrate: G3P + NAD^+ + P_i
  • Product: 1,3-bisphosphoglycerate + NADH + H^+
  • Reaction: Glyceraldehyde-3-phosphate+NAD++Pi→1,3−bisphosphoglycerate+NADH+H+\text{Glyceraldehyde-3-phosphate} + \text{NAD}^+ + \text{P}_i \rightarrow 1,3-\text{bisphosphoglycerate} + \text{NADH} + \text{H}^+

Step 7: Phosphoglycerate kinase

  • Substrate: 1,3-bisphosphoglycerate + ADP
  • Product: 3-phosphoglycerate + ATP
  • Enzyme: Phosphoglycerate kinase
  • Reaction: 1,3−bisphosphoglycerate+ADP→3−phosphoglycerate+ATP1,3-\text{bisphosphoglycerate} + \text{ADP} \rightarrow 3-\text{phosphoglycerate} + \text{ATP}
  • Note: Substrate-level phosphorylation

Step 8: Phosphoglycerate mutase

  • Substrate: 3-phosphoglycerate
  • Product: 2-phosphoglycerate
  • Reaction: 3-phosphoglycerate→2-phosphoglycerate\text{3-phosphoglycerate} \rightarrow \text{2-phosphoglycerate}

Step 9: Enolase

  • Substrate: 2-phosphoglycerate
  • Product: Phosphoenolpyruvate (PEP) + H2O
  • Enzyme: Enolase
  • Reaction: 2−phosphoglycerate→phosphoenolpyruvate+H2O2-\text{phosphoglycerate} \rightarrow \text{phosphoenolpyruvate} + \text{H}_2\text{O}

Step 10: Pyruvate kinase

  • Substrate: PEP + ADP
  • Product: Pyruvate + ATP
  • Enzyme: Pyruvate kinase
  • Reaction: PEP+ADP→pyruvate+ATP\text{PEP} + \text{ADP} \rightarrow \text{pyruvate} + \text{ATP}
  • Note: Substrate-level phosphorylation; end of glycolysis

Net energy yield

  • ATP produced: 4 per glucose
  • ATP consumed: 2 per glucose
  • Net ATP: Net ATP=2\text{Net ATP} = 2
  • NADH produced: 2 per glucose
  • End product: Pyruvate

References (per transcript)

  • Byjus.com
  • Vedantu.com
  • Microbenotes.com
  • Principles of Plant Physiology: SL Kochar and Sukhbir Kaur