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Pyruvate Oxidation
(Aerobic )
Krebs cycle
Electron Transport Chain
Two mechanisms for generating ATP
• Substrate level phosphorylation (directly) – responsible for 4 of 36 ATP made
• Oxidative phosphorylation (indirectly) – responsible for remaining 32 ATP made
much more to come later…
6O2 -------> 6CO2 + 6H2O +
(Δ G = - 2870 KJ/mol glucose)
Oxygen is not the only possible electron acceptor in the oxidation of glucose in a cell.
obligate anaerobes – micro-organisms that use NO2, SO4, CO2 as final electron
acceptors (cannot live in the presence of oxygen)
obligate aerobes – most animals, plants, fungi and bacteria require oxygen as the
final electron acceptor (most eukaryotes)
facultative anaerobes – organisms that can tolerate aerobic and anaerobic conditions
(mostly bacteria)
• designed to increase surface area for oxygen to bind (why is lots of Oxygen
• Pyruvate oxidation, Kreb’s cycle (citric acid cycle) and ETC occur inside
Glycolysis (sugar-splitting)
• occurs in the cytoplasm
• first 10 reactions of cellular respiration
• glucose backbone is essentially split in half
Glycolysis is not highly efficient in energy harnessing;
2 ATP x 30.5 KJ/mol = 61 KJ
total free energy in 1 mol of glucose = 2870 KJ
energy conversion efficiency = 61 KJ x 100% = 2.1%
2870 KJ
Glycolysis is most likely the earliest form of metabolism, provides enough energy for
smaller simple organisms, but does not provide enough energy for multicellular
2 ATP molecules are used in first 5 steps
these reaction essentially prime the glucose molecule by adding phosphates (costs)
Fructose 1,6-bisphosphate is split into dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3phosphate (G3P).
(DHAP is quickly converted to G3P)
2 NADH molecules are produced as 2 molecules of G3P processed
2 ATP are produced by substrate level phosphorylation, as 1,3 bisphosphoglycerate (BPG) are processed
2 more ATP are produced by substrate level phosphorylation as 2 molecules of phosphoenolpyruvate
(PEP) are converted to pyruvate molecules
Overall Equation
Glucose + 2ADP + 2Pi + 2NAD+ -----> 2 pyruvate + 2ATP + 2 (NADH + H+)
4 ATP produced
2 ATP used
2 ATP produced (net)
2 NADH produced (for further processing)
Pyruvate Oxidation…