Aerobic Respiration:Glycolysis, Pyruvate Oxidation & the Citric
Acid Cycle
Glycolysis!
• found in almost all living organisms
• occurs in the cytoplasm
• does not require oxygen
• first stage of aerobic cellular respiration
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?
Investment (#1-3)• glucose undergoes two
phosphorylations & an isomerization
• 2 ATP are invested
Cleavage (#4-5)• splits into two 3-carbon molecules: G3P & DHAP
• DHAP isomerizes into G3P
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)
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
• Before pyruvate enters the Krebs Cycle, it is oxidised in the transition step.
!• Pyruvate molecules
are actively transported into the mitochondrial matrix.
The Transition Reaction -Pyruvate Oxidation
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
The Citric Acid Cycle (Krebs)
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.
The Krebs Cycle
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?