pyruvate oxidation - stage 2
- occurs in only in mitochondria of eukaryotes
- 1st forms acetyl-CoA from pyruvate, then oxidizes acetyl-CoA in Krebs cycle
- single "decarboxylation" reaction that cleaves off one of the carbons on pyruvate (producing acetyl group and CO2)
- catalyzed in mitochondria by multienzyme complex
- pyruvate dehydrogenase - enzyme that removes CO2 from pyruvate; has 60 subunits
- pyruvate + NAD+ + CoA (coenzyme A) >> acetyle-CoA + NADH + CO2
- acetyl-CoA - produced by a large number of metabolic processes
- key point for many catabolic processes in eukaryotes
- used for fatty acid synthesis instead of Krebs cycle when ATP levels are high
Krebs cycle - stage 3
- 9 reactions; oxidation of acetyle-CoA
- takes place in mitochondria matrix
- combines acetyle-CoA (2-carbon molecule) w/ oxaloacetate (4-carbon molecule) to extract electrons and CO2 to power proton pumps for ATP
- step A - priming; 3 reactions rearrange chemical groups in acetyl-CoA to prepare the 6-carbon molecule for energy extraction
- step B - energy extraction; 4/6 reactions oxidize and remove electrons
- reaction 1 - condensation
- acetyle-CoA combines w/ oxaloacetate to form citrate
- irreversible reaction; inhibited when ATP concentration is high
- reaction 2/3 - isomerization
- repositions hydroxyl group by taking away H2O and adding it back to a different carbon
- forms isocitrate from citrate
- reaction 4 - 1st oxidation
- oxidized to yield pair of electrons that make NADH from a NAD+
- decarboxylated to split off a CO2 to form a-ketoglutarate (5-carbon molecule)
- reaction 5 - 2nd oxidation
- a-ketoglutarate decarboxylated into succinyl group, which bonds to coenzyme A to form succinyl-CoA
- CO2 removed
- oxidized to yield pair of electrons that make NADH from a NAD+
- reaction 6 - substrate-level phosphorylation
- bond between succinyl group (4-carbon molecule) and CoA cleaved to phosphorylate GDP into GTP
- GTP readily converts into ATP
- succinyl-CoA becomes succinate
- reaction 7 - 3rd oxidation
- succinate oxidized into fumarate
- energy produced not enough for NAD+, so FAD turned into FADH2 instead
- FAD part of inner mitochondrial membrane, can't diffuse within the organelle
- reaction 8/9 - oxaloacetate regeneration
- H2O added to fumarate, making malate
- malate oxidized to form oxaloacetate and 2 electrons to form NADH from NAD+
- by end of Krebs cycle, ener
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