Integrated SequencePhysics Chemistry Organic Biology

Web Resources

The Medical Biochemistry Page - Complexes of the Electron Transport Chain
Excellent discussion at the level of introductory biochemistry.



  click if a link is broken



Special points of emphasis

Work, Energy, and Power

Electricity

The Chemical Bond

Chemical Thermodynamics and the Equilibrium State

Oxidation-Reduction

Electrochemistry

Bioenergetics and Cellular Respiration

The free energy decrease (positive cell potential) driving oxidative phosphorylation is free energy of oxidation of NADH or FADH2 by O2. NADH and FADH2 are excellent electron carriers. While normally an oxidation process whereby a nitrogen atom loses electron control would not be particularly favored, with NADH and FADH2, oxidation leads to a marked increase in resonance stabilization, the nicotinamide ring of NAD+ actually becoming aromatic through the process, so the typical love of nitrogen for electrons is counterbalanced by resonance so that the nitrogens of NADH and FADH2 will give the electrons they carry to the respiratory chain without the need for significant increase to the internal energy of the system. The electrons begin at high energy, and as they fall towards the deep potential energy well represented by strong covalent bonds with oxygen in the final state, the crank is turned in the cytochromes, pumping protons into the outer compartment, storing the energy which drives ATP synthesis in chemiosmosis.



The Chemical Bond

Conjugated π Systems and Aromaticity

Coordination Chemistry

Proteins

Oxidation-Reduction

Electrochemistry

Bioenergetics and Cellular Respiration

Blood

Evolution

Coordinated iron and copper ions serve vital rolls in the enzyme complexes of the respiratory chain. One important type of prosthetic group are iron-sulfur clusters in which iron is coordinated to sulfhydral groups of cycsteine as well as inorganic sulfides. In these groups the iron atoms interchange from the reduced form, Fe2+ , to the oxidized form, Fe3+ . Three of the enzyme complexes of the respiratory chain are cytochromes, which means they are electron transferring proteins containing heme groups. Reduction of the iron corresponds to electron delocalization over the entire porphyrin network.

The design of cytochrome c is more than a billion years old, common to all eukaryotic cells.




Work, Energy, and Power

Electricity

Thermochemistry

Chemical Thermodynamics and the Equilibrium State

Acids and Bases

Biological Membranes

The Eukaryotic Cell

Oxidation-Reduction

Electrochemistry

Bioenergetics and Cellular Respiration

DC Current

The impulse for the movement of electrons from NADH to O2 in the respiratory chain on the inner mitochondrial membrane is similar to the voltage source in a galvanic cell. Protons are pumped at three sites, the NADH-Q reductase complex, cytochrome reductase, and cytochrome oxidase. The movement of electrons from FADH2 to O2 moves only two protons because FADH2 releases its electrons directly to Q (ubiquinone), bypassing NADH-Q reductase. The resistive load or work coupled to this expenditure of free energy (current flowing through a positive cell potential) is the pumping of protons from the matrix into the intermembrane space. The respiratory chain pushes the protons uphill against a pH gradient of 1.4 and against a membrane potential of .14 V (electric field across the inner mitochondrial membrane). The movement of protons from the matrix to the intermembrane space stores free energy across the inner mitochondrial membrane. The free energy change associated with each electron movement (1) NADH to NADH-Q reductase (2) cytochromes b to c1 in cytochrome reductase (3) cytochrome a to O2 is sufficient to move a proton across the membrane against a free energy gradient. The energy stored in each such proton movement is sufficient to drive ATP synthesis with oppositely directed proton flow.







The WikiPremed MCAT Course is a free comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum.

Please read our policies on privacy and shipping & returns.  Contact Us.
MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course.


Creative Commons License
The work of WikiPremed is published under a Creative Commons Attribution Share Alike 3.0 License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions. You can use the resources here for commercial or non-commercial purposes, but please give attribution and a link to the production credits and edit history of the resource. For the works here which began as my individual work, please attribute "John Wetzel, an author at wikipremed.com".