2. What is Glycolysis?
Glycolysis is the sequence of reactions that convert glucose into pyruvate in
the presence of oxygen (aerobic)
or
lactate in the absence of oxygen (anaerobic) with the production of ATP.
Embden Meyerhof pathway.
Location: Cytosol of all cells / Cytoplasm.
Pathway: The breakdown of glucose (6-carbon compound) to two moles of
pyruvate (3-carbon compound) is brought about by sequential action of ten
enzymes which can be divided into two phases.
Ist phase: Energy requiring phase or preparative phase
IInd phase: Energy generating phase.
5. Keys to remember:
Starting substrate: Glucose
End product: Pyruvate(Aerobic) & Lactate (Anaerobic)
Total Substrate: 12 ( countable 11)
Total Steps: 11 (Countable 10)
Total Enzymes: 11
ATP: -1, -3 & +6, +9.
NAD: 5 , 10
Water: 8
6. Energetics of Glycolysis:
Net production of ATP in aerobic glycolysis = Number of ATP produced minus number of ATPs
consumed = 10 – 2 = 8
It is assumed that NADH formed in glycolysis uses malate shuttle to produce 6 ATPs
Total ATP per molecule of glucose under anaerobic glycolysis = 2
Reaction Reaction catalyzed by
No. of ATP formed or
consumed per glucose
molecule
Glucose to glucose-6-phosphate Hexokinase, glucokinase -1
Fructoe-6-phosphate to fructose 1,6
biphosphate
Phosphofructokinase -1
Glyceraldehyde-3-phosphate to 1,3-
bisphosphoglycerate
Glyceraldehyde-3-phosphate
dehydrogenase
+6*
1,3-bisphosphoglycerate to 3-
phosphoglycerate
Phosphoglycerate kinase +2
Phosphoenolpyruvate to Pyruvate Pyruvate kinase +2
7. Under anaerobic conditions [oxidation of glucose to lactate]
Total ATP used = 2 ……….. as follows,
One ATP in the activation of glucose to glucose-6-phosphate.
One ATP in the activation of fructose-6-phosphate to
fructose1,6-bisphosphate.
Total ATP gained = 4 ………. as follows,
2 ATP by substrate level phosphorylation from 1,3-bis
phosphoglycerate
2 ATP from substrate level phosphorylation from phosphoenol -
pyruvate.
Net ATP gained = 4 ATP gained - 2 ATP used = 2 ATP
8. :
Under Aerobic conditions
Total ATP used = 2 ATP as under Anaerobic conditions
Total ATP gained = 10 ATP, generated as follows,
4 ATP (obtained by substrate level phosphorylation) +
6 ATP, obtained after complete oxidation of 2 NADH
molecules in respiratory chain.
Net ATP gained = 8 ATP as follows,
10 ATP gained – 2 ATP used = 8 ATP
9. Significance:
Glycolysis -principal route -glucose metabolism.
Glycolysis provides ATP.
It provides pyruvate needed for Krebs' cycle.
Generates precursors for biosynthetic pathway, e.g.
Pyruvate amino acid (alanine).
pyruvate acetyl-CoA fatty acid.
Glycerol-3-phosphate triacylglycerol
Reversal of glycolysis [ with 3 more steps] is gluconeogenesis, an
important source of glucose.
10. Comparison of Aerobic and Anaerobic Glycolysis
Occurs in presence of oxygen
Pyruvate is the end product
Oxidation of NADH in the
electron transport chain.
08 Net ATP produced
Occurs in absence of oxygen
Lactate is the end product.
No oxidation of NADH in the
electron transport chain.
02 Net ATP produced
