Q.Give an account of glycolysis. Where does it occur? What are the end products? Trace the fate of these products in both aerobic and anaerobic respiration.
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Start your 14-day free trial to unlock the full solution →Glycolysis breaks one glucose into two pyruvic acid molecules in the cytoplasm, with a net gain of 2 ATP and 2 NADH; the pyruvate is fully oxidised via Krebs cycle and ETC in aerobic respiration (much ATP + CO2 + water), or converted to ethanol + CO2 or lactic acid in anaerobic respiration (fermentation).
Glycolysis (from 'glycos' = sugar, 'lysis' = splitting) is the process of partial oxidation of glucose into two molecules of pyruvic acid. It is also called the EMP pathway (Embden-Meyerhof-Parnas pathway). It is the first step of respiration and is common to both aerobic and anaerobic respiration.
Where it occurs: Glycolysis takes place in the cytoplasm (cytosol) of the cell. It does not require oxygen.
Outline of the process:
- Glucose (6C) is first phosphorylated using ATP to form glucose-6-phosphate, then fructose-6-phosphate, and then fructose-1,6-bisphosphate (using another ATP). Thus 2 ATP are invested.
- Fructose-1,6-bisphosphate splits into two 3-carbon molecules (glyceraldehyde-3-phosphate).
- Through further steps, each 3-carbon molecule is converted to pyruvic acid, releasing energy that produces ATP and NADH.
End products (per glucose):
- 2 molecules of pyruvic acid (3C each),
- a net gain of 2 ATP (4 produced minus 2 used),
- 2 molecules of NADH + H+.
Fate of the products (pyruvic acid):
(a) In aerobic respiration (in presence of oxygen):
- Pyruvic acid moves from the cytoplasm into the mitochondrion.
- It undergoes oxidative decarboxylation to form acetyl-CoA (releasing CO2 and NADH).
- Acetyl-CoA enters the Krebs cycle (citric acid cycle), where it is completely oxidised to CO2, producing NADH, FADH2 and some ATP.
- The NADH and FADH2 pass their electrons to the electron transport chain (ETC), where oxygen is the final electron acceptor and forms water; this drives oxidative phosphorylation producing a large amount of ATP. …
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