citric acid cycle

• Pyruvate entering the mitochondrial matrix

  Finding Coenzyme A, undergoing decarboxylation, oxidation by NAD+, and attachment to Coenzyme A to generate acetyl CoA
• Higher organisms like animals evolved additional metabolic pathways that generate far more energy than glycolysis
• First simple organisms on earth were able to generate energy through glycolysis for millions of years
• Fourth step of the citric acid cycle

  Ketoglutarate dehydrogenase further oxidizes alpha-ketoglutarate by NAD+ to form succinyl-CoA
• Third step of the citric acid cycle

  Isocitrate dehydrogenase oxidizes isocitrate by NAD+ and then decarboxylates to form alpha-ketoglutarate
• Plants covering the earth filled the atmosphere with oxygen, allowing for large-scale oxygen-dependent aerobic respiration
• Fifth step of the citric acid cycle

  Succinyl-CoA synthetase displaces Coenzyme A with a phosphate group to form succinate, producing one molecule of GTP
• First step of the citric acid cycle

  Citrate synthase removes the acetyl group and tacks it onto oxaloacetate to form citrate
• Glycolysis


  An anaerobic process that does not require oxygen to occur
• Two ATPs per glucose are generated in glycolysis
• Seventh step of the citric acid cycle

  Fumarase catalyzes hydration to form malate
• The products of the citric acid cycle move on to oxidative phosphorylation, which generates the majority of the ATP produced in aerobic respiration
• According to endosymbiotic theory, mitochondria were incorporated into eukaryotes for their respiratory abilities
• Second step of the citric acid cycle

  Aconitase removes a water molecule and adds another to generate isocitrate
• For every acetyl CoA that enters the citric acid cycle, three NADHs, one FADH2, and one ATP are produced
• Citric acid cycle


  An eight-step pathway requiring eight separate enzymes
• Each glucose molecule will produce two acetyl CoAs in glycolysis, doubling the amounts per glucose molecule
• Sixth step of the citric acid cycle

  Succinate dehydrogenase oxidizes succinate by FAD to form fumarate and FADH2
• The location in the cell where aerobic respiration occurs is the mitochondria, eukaryotic cell organelles
• Eighth step of the citric acid cycle

  Malate dehydrogenase oxidizes malate by NAD+ to give oxaloacetate, restarting the cycle