Structure of ATP synthase, the F0 proton channel and rotating stalk are shown in blue, the F1 synthase domain in red and the membrane in grey.

Structure of ATP synthase, the F0 proton channel and rotating stalk are shown in blue, the F1 synthase domain in red and the membrane in grey.

In oxidative metabolism, the electron pairs liberated through the oxidation of glucose do not pass directly to O2. The direct oxidants are the coenzymes of various oxidoreductases. The reduced forms of these coenzymes, NADH and FADH2, then transfer these electrons into the electron transport system which is located on the mitochondrial matrix. ATP is formed through an energy coupling process that begins with reoxidation of NADH and FADH2. The electrons passing from NADH and FADH2 travel through a sequential oxidation-reduction process involving a long series of redox centers located within a series of protein complexes in the inner mitochondrial membrane. As electrons pass along the chain, protons are expelled from the mitochondrial matrix by various mechanisms. The free energy stored in the resulting concentration and electric potential gradient (proton motive force) drives the synthesis of ATP as the protons flow back to the mitochondrial matrix through the protein complex ATP synthase.

WikiPremed Resources

Biosynthesis of Macromolecules Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Oxidative Phosphorylation
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals


Understand how the structure of a mitochondrion supports its role in oxidative metabolism.

Be prepared to describe the path of electrons through the electron transport chain in the mitochondrion.

Be able to describe the structural changes undergone by the electron carriers NADH and FADH2 in their oxidation-reduction cycle in terms that explain their suitability as electron carriers.

Understand how flavins, iron-sulfur complexes, quinones and hemes transfer electrons within the electron transport chain.

Know the steps of the ubiquinone cycle in electron transfer with Q-cytochrome c oxidoreductase.

Comprehend the process by which the electrochemical gradient from the inter-membrane space into the matrix in mitochondria drives the activity of ATP synthase.

Suggested Assignments

The question server contains a large, general section that covers a number of topics from metabolism including glycolysis, the citric acid cycle, and oxidative phosphorylation. After warming up with the terminology complete the crossword puzzle for energy metabolism. Here is the solution to the puzzle.

Read pp. 81-86 in ExamKrackers Biology I. Perform practice items 65-72 on pg. 87. (This is a combined treatment of the citric acid cycle and oxidative phosphorylation).

Review the web resources for oxidative phosphorylation.

Conceptual Vocabulary for Oxidative Phosphorylation

Glycolysis & Pyruvate Dehydrogenase

Each list begins with basic conceptual vocabulary you need to know for MCAT questions and proceeds to advanced terms that might appear in context in MCAT passages. The terms are links to Wikipedia articles.
Anaerobic organism
An anaerobic organism is any organism that does not require oxygen for growth.
Adenosine triphosphate
Adenosine triphosphate is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer.
Glycolysis is the initial process of most carbohydrate catabolism serving the functions of producing ATP and NADH, pyruvate for the citric acid cycle, and a variety of other compounds which are important for biosynthesis.
Pyruvic acid
Pyruvic acid is an alpha-keto acid which plays an important role in biochemical processes. It is an output of glycolysis.
Glucose 6-phosphate (also known as Robison ester) is glucose sugar phosphorylated on carbon 6.
Fermentation is respiration under anaerobic conditions with no external electron acceptor.
Ethanol fermentation
Ethanol fermentation is the biological process by which sugars such as glucose, fructose, and sucrose, are converted into ethanol and carbon dioxide.
A kinase, alternatively known as a phosphotransferase, is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific target molecules.
Phosphorylation is the addition of a phosphate group to a protein molecule or a small molecule.
Fructose 2,6-bisphosphate
Fructose 2,6-bisphosphate, is a metabolite that allosterically affects the activity of the enzymes phosphofructokinase 1 and fructose 1,6-bisphosphatase to regulate glycolysis and gluconeogenesis.
Futile cycle
A futile cycle is when two metabolic pathways run simultaneously in opposite directions and have no overall effect other than wasting energy.
Fructose 6-phosphate
Fructose 6-phosphate (also known as the Neuberg ester) is fructose sugar phosphorylated on carbon 6. The beta-D-form of this compound is very common in cells.
L-lactate is constantly produced in animals from pyruvate in a process of fermentation during normal metabolism and exercise.
Lactic acid fermentation
Lactic acid fermentation is a form of anaerobic respiration that occurs in some bacteria and animal cells in the absence of oxygen.
Adenosine monophosphate
Adenosine monophosphate is an ester of phosphoric acid with the nucleoside adenosine. AMP consists of the phosphate group, the pentose sugar ribose, and the nucleobase adenine.
Substrate-level phosphorylation
Substrate-level phosphorylation is a type of chemical reaction that results in the formation of ATP by the direct transfer of a phosphate group to ADP from a reactive intermediate.
Pyruvate decarboxylation
The pyruvate decarboxylation reaction links the metabolic pathways glycolysis and the citric acid cycle.
In glycolysis and photosynthesis, 1,3-Bisphosphoglycerate (1,3BPG) is a transitional stage between glycerate 3-phosphate and glyceraldehyde 3-phosphate during the fixation or reduction, respectively, of carbon dioxide.
2-Phosphoglycerate (2PG) is a glyceric acid which serves as the substrate in the ninth step of glycolysis. It is catalyzed by enolase into phosphoenolpyruvate (PEP), the penultimate step in the conversion of glucose to pyruvate.
A hexokinase is an enzyme that phosphorylates a six-carbon sugar, a hexose, to a hexose phosphate.
Enolase, or 2-phospho-D-glycerate hydrolyase, is an enzyme that participates in glycolysis, catalyzing the conversion of 2-phosphoglycerate to phosphoenolpyruvate, the penultimate step in the conversion of glucose to pyruvate.
Pyruvate kinase
Pyruvate kinase is an enzyme involved in glycolysis, catalyzing the transfer of a phosphate group from phosphoenolpyruvate (PEP) to ADP, yielding a pyruvate molecule and producing one molecule ATP.
Pyruvate dehydrogenase complex
Pyruvate dehydrogenase complex (PDC) is a complex of three enzymes that transform pyruvate into acetyl-CoA.
Entner-Doudoroff Pathway
The Entner-Doudoroff pathway in some prokaryotes describes a series of reactions that catabolize glucose to pyruvate using a different set of enzymes from those used in either glycolysis or the pentose phosphate pathway.
Aldolase A
Aldolase A is an enzyme which catalyses one of the aldol reactions of glycolysis in which fructose 1,6-bisphosphate is broken down into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.
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