Aerobic Respiration

Pyruvate Oxidation

The Citric Acid Cycle

What happens to pyruvate?

• depends on whether oxygen is present (aerobic respiration) or not (anaerobic respiration)

Pyruvate Oxidation

• if oxygen is present, the pyruvate molecules are transported from the cytoplasm into the mitochondrial matrix

Pyruvate Oxidation

Pyruvate Oxidation

• 3 enzyme-catalyzed changes:

• decarboxylation forming CO2 as a by-product

• oxidation of the 2-carbon molecule, causing a reduction of NAD+ to NADH

• attachment of coenzyme A (a derivative of vitamin B5), forming acetyl-CoA

Pyruvate Oxidation

The Citric Acid Cycle

(Also known as the Krebs Cycle)

The Citric Acid Cycle

• 8 enzyme-catalyzed reactions• occurs in the mitochondrial matrix• aerobic process• cyclic process: oxaloacetate is the

reactant of the first reaction and product of the last reaction

First reaction

Citric Acid Cycle Pathway

Major Processes:Decarboxylation (Reactions 3 & 4)

• 2 different reactions involve the removal of carbon as CO2

Major Processes:Oxidation (Reactions 3, 4, 6, 8)

• H atoms (with their associated electrons) are transferred to a coenzyme (NAD+ or FAD)

Major Processes:Energy Production (Reaction 5)

• during one of the reactions, ATP is generated by substrate-level phosphorylation.

• it is coupled to a reaction which has a large amount of free energy release

Summary

• oxaloacetate is regenerated in the last step

• all 6 carbons from glucose have been oxidized to CO2

• all of the energy from glucose is in the form of ATP, NADH and FADH2

Krebs Cycle Overall Reaction

2 acetyl CoA + 6NAD+ + 2 FAD + 2ADP + 2 Pi

4 CO2 + 6 NADH + 6 H+ + 2 FADH2 + 2 ATP

Summary

Animations

• Simple reaction review: http://www.science.smith.edu/departments/Biology/Bio231/krebs.html

• Animation & Quiz: http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html

Preview of ETC…

• If you’re confused about the Electron Transport Chain, this animation might help:

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120071/bio11.swf::Electron%20Transport%20System%20and%20ATP%20Synthesis