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?