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Aerobic Respiration: Glycolysis, Pyruvate Oxidation & the Citric Acid Cycle
Image of glucose powder from:
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Glycolysis found in almost all living organisms
occurs in the cytoplasm does not require oxygen first stage of aerobic cellular respiration
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Reactions of Glycolysis
10 enzyme-catalyzed reactions 6-carbon glucose is split into two 3-carbon pyruvate molecules net energy gain of 2 ATP 2 NAD+ are reduced to NADH occurs in three stages
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What does the term phosphorylation mean?
What does isomerization mean?
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Investment (#1-3) glucose undergoes two phosphorylations & an isomerization 2 ATP are invested Phosphorylation: glucose --> glucose-6-phosphate Isomerization: G6P --> fructose 6-phosphate Phosphorylation F6P --> fructose 1,6-biphosphate Image from:
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Cleavage (#4-5) splits into two 3-carbon molecules: G3P & DHAP
DHAP isomerizes into G3P Image from: olysis.htm
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Energy pay-off (#6-10) 4 ATP are made (net 2 ATP)
some electrons & protons are released & stored for ETC (2 NADH) Final result: 3-carbon pyruvate (x2) Image from:
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2 pyruvate + 2 NADH + 2 H+ + 2 ATP
Energy Yield 2 NADH per glucose molecule 2 molecules of ATP are used 4 molecules of ATP are produced overall net yield of 2 ATP per glucose molecule Net Equation glucose + 2 NAD+ + 2 ADP + 2 Pi -----> 2 pyruvate + 2 NADH + 2 H+ + 2 ATP
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Aerobic Respiration: Glycolysis, Pyruvate Oxidation & the Citric Acid Cycle
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The Transition Reaction -Pyruvate Oxidation
Before pyruvate enters the Krebs Cycle, it is oxidised in the transition step. Pyruvate molecules are actively transported into the mitochondrial matrix.
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The Transition Reaction -Pyruvate Oxidation
Carbon dioxide is removed from the pyruvate Hydrogen atoms are removed and transferred to NAD+. reactions are carried out by enzymes A 2-carbon compound called an acetyl group is formed & is attached to coenzyme A. The resulting acetyl CoA can enter the Citric Acid Cycle.
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If no ATP is created in the pyruvate oxidation stage, does that mean no energy is harvested?
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Aerobic Respiration: Glycolysis, Pyruvate Oxidation & the Citric Acid Cycle
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The Citric Acid Cycle (Krebs)
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The Citric Acid (Krebs) Cycle
Acetyl CoA from the transition step is combined with a 4C compound called oxaloacetate, forming 6C citrate. Citrate undergoes a series of decarboxylation and dehydrogenation reactions which result in the regeneration of oxaloacetate.
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The Krebs Cycle
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Products of the Krebs Cycle
Each turn of the Krebs Cycle produces: 4 molecules of reduced NAD+ (1 from Pyr Ox) 1 molecule of reduced FAD 1 molecule of ATP 3 molecules of CO2 (1 from Pyr.Ox.) The Krebs Cycle turns twice for every glucose molecule broken down; per glucose molecule the yield is doubled: 8 NAD+; 2 FAD; 2ATP and 6 CO2
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What is left of the glucose molecule at the end of the citric acid cycle?
How many ATP have been produced so far?
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