Aerobic Respiration

The model for aerobic respiration is the oxidation of the glucose molecule:

(1) C₆H₁₂O₆ + 6 O₂ + 6 H₂O + 38 ADP +38 P è 6 CO₂ + 12 H₂O + 38 ATP + 420 Kcal

This equation has an oxidation component,

(2) C₆H₁₂O₆ è 6 CO₂

And a reduction component:

(3) 6 O₂ è 6 H₂O

Aerobic respiration has four stages

1. Glycolysis –

· Process occurs in the cytoplasm;

· A six-carbon glucose molecule is converted to two, 3-carbon molecules of pyruvate

· This process occurs in the cytoplasm.

· In order to initiate the process, 2 molecules of ATP are consumed. Four molecules of ATP and 2 molecules of NADH are produced;

2. Formation of acetyl coenzyme A –

· Process involves shuttling pyruvate molecules into mitochondrion

· Each pyruvate molecules is oxidized to carbon dioxide and a 2-carbon acetyl group.

· The carbon dioxide is released as a waste product, and the 2-carbon acetyl group is bound to coenzyme A and brought into the mitochondrion;

3. The citric acid cycle –

· Each of the 2-carbon acetyl groups produced from the original glucose molecule is bonded to a pre-existing molecule of oxaloacetate to form citrate (i.e. citric acid).

· These two citric acid molecules are gradually oxidized, and the hydrogen ions are bound to NAD to form NADH and to FAD to form FADH₂.

· Oxaloacetate is produced when the last carbon atom is released in the form of carbon dioxide;

· Two ATP molecules are synthesized for each glucose molecule entering the cell.

4. Electron transport chain and chemiosmosis –

· The electrons removed from the molecules in glycolysis and citric acid follow a series of cytochromes on the mitochondrial membrane,

· Hydrogen ions (protons) are pumped across the inner membrane of the mitochondrion.

· These protons flow through ATP synthase enzyme molecules, and thereby release energy which drives the formation of 34 ATP molecules.

Citric acid cycle

• Each of the 2-carbon acetyl groups produced from the original glucose molecule is bonded to a pre-existing molecule of oxaloacetate to form citrate (i.e. citric acid). These two citric acid molecules are gradually oxidized, and the hydrogen ions are bound to NAD to form NADH and to FAD to form FADH₂. Oxaloacetate is produced when the last carbon atom is released in the form of carbon dioxide.

 Video clip summarizing the citric acid (Krebs) cycle:
http://www.youtube.com/watch?v=JNd4QQXluJ0&feature=related

Having played the trombone in high school marching band, I have a soft spot in my heart for THIS version:
http://www.youtube.com/watch?v=FgXnH087JIk

Electron Transport System/Chemiosmosis

The electrons removed from the molecules in glycolysis and citric acid follow a series of cytochromes on the mitochondrial membrane, while the hydrogen ions (protons) are pumped across the inner membrane of the mitochondrion. The fluid is this sector of the mitochondrion has, therefore, a very low pH. These protons flow through ATP synthase enzyme molecules, and thereby release energy which drives the formation of ATP molecules.

The last step in aerobic respiration is the bonding of 2 electrons, 2 protons, and oxygen to form water.

A video clip summarizing chemiosmosis:
http://www.youtube.com/watch?v=Btl0ltsw4m0

Aerobic respiration is much more efficient at extracting chemical energy than is fermentation:

Efficiency of Fermentation versus Aerobic Respiration
	Fermentation	Aerobic Respiration
Total free-energy change during reaction	56 kcal	686 kcal
ATP synthesized (net gain)	2	36
Total free energy stored as high-energy phosphate bonds	14 kcal	252 kcal
Efficiency of recapturing usable energy from total energy released	25%	37%
Fraction of total available free energy from glucose molecule recaptured as ATP	2%	37%