In the presence of oxygen pyruvate is transported into the mitochondria where it
enters the next major metabolic pathway for the production of ATP energy. The
citric acid cycle. Aerobic.
If there is no oxygen present then the pyruvate is converted to a substance called
• The Electron Transport Chain and Proton Pumping
• Chemiosmotic Phosphorylation
• Imbedded in the inner mitochondria membrane are a series of
electron carriers. These electron carriers pass electrons from
NADH and FADH to one another down a red-ox stairway. The net
result of this series of step-wise electron exchanges is to pump H+
(protons) out of the matrix into the outer compartment between the
outer and inner membrane of the mitochondria.
• This process establishes a steep proton gradient across the inner
mitochondrial membrane. This creates a great deal of potential
energy across the inner membrane.
• This potential energy can be harnessed by an enzyme system to
form ATP from ADP + Pi. This is known as chemiosmotic
• For each 2H+ 1 ATP is created. Therefore
since each NADH causes 6 H+s to be
pumped out 3 ATP can be made for each
NADH entering the respiratory chain.
• Also each FADH2 can pump 4 H+s.
Therefore each FADH2 can cause 2ATP to
• Glucose is not the only material that can be
metabolized to generate energy. Many
carbohydrates can be broken down in glycolysis
and enter the Krebs Cycle. Proteins can be
broken down into amino acids and those can be
deaminated and the carbon chains feed into the
Krebs Cycle. The very long carbon chains of
fatty acids can be chopped into two carbon
pieces by a process known as Beta Oxidation.
Since the fatty acid chains can be up to 20
carbons long there is a very great deal of energy
stored in fats.