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Glycolysis and Krebs

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C2 ATP

GlycolysisElectron

Transport Chain

32 ATP

6O2

6H2O

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CPyruvate oxidation

CO2C2

Citric Acid Cycle

2 ATP

CO2C4

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GLYCOLYSIS

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

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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1. Why is glycolysis considered to be the most fundamental and probably the most ancient of all metabolic pathways?

2.How many free phosphates were used in the reaction? 3. How efficient is glycolysis at converting glucose to ATP? b. Are there other high-energy products of glycolysis? 4. a. If (pyruvate) kinase was non-functional how would

that affect glycolysis? Cellular respiration? b. What would be detected by biochemists in the cell that would indicate (pyruvate) kinase was non-functional?

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How the Krebs Cycle Works (animation)

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Aerobic Respiration:Glycolysis, Pyruvate Oxidation & the Citric

Acid Cycle

• Before pyruvate enters the Krebs Cycle, it is oxidized in the transition step.

• Pyruvate molecules are actively transported into the mitochondrial matrix.

`• 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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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.

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The Krebs Cycle

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Krebs!!

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