Q.Give a detailed account of glycolysis (EMP pathway). OR Explain the mechanism of fermentation.
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Start your 14-day free trial to unlock the full solution →Glycolysis (the Embden-Meyerhof-Parnas or EMP pathway) occurs in the cytoplasm and converts one molecule of glucose into two molecules of pyruvic acid through a 10-step sequence, with a net gain of 2 ATP and 2 NADH — common to both aerobic and anaerobic respiration.
Option (a): Glycolysis (EMP pathway)
Glycolysis takes place in the cytoplasm of the cell and is common to both aerobic and anaerobic modes of respiration. In this pathway, one molecule of glucose (6-carbon) is partially oxidised and split into two molecules of pyruvic acid (3-carbon), through the following broad steps:
- Glucose is phosphorylated to glucose-6-phosphate, consuming 1 ATP.
- It is isomerised to fructose-6-phosphate.
- This is phosphorylated to fructose-1,6-bisphosphate, consuming a second ATP.
- Fructose-1,6-bisphosphate is split into two 3-carbon molecules — dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P); DHAP is also converted to G3P, so effectively two molecules of G3P proceed further.
- Each G3P is oxidised and phosphorylated to 1,3-bisphosphoglycerate, generating NADH.
- This is dephosphorylated to 3-phosphoglyceric acid, generating ATP by substrate-level phosphorylation.
- It is converted via 2-phosphoglycerate and then dehydrated to phosphoenolpyruvate (PEP).
- PEP is finally converted to pyruvic acid, generating a further ATP.
Since these last steps happen twice (once for each 3-carbon fragment), glycolysis has a gross yield of 4 ATP and 2 NADH, but since 2 ATP were consumed early on, the net yield is 2 ATP and 2 NADH per glucose molecule, along with 2 pyruvate molecules.
Option (b): Mechanism of fermentation
Fermentation is the anaerobic breakdown of pyruvic acid (from glycolysis), regenerating NAD+ so glycolysis can continue, but without complete oxidation and with much less energy release than aerobic respiration. There are two common types:
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