- Information
- AI Chat
Electron transport chain
Mammalian Physiology (PHOL0001)
University College London
Recommended for you
Preview text
The Electron Transport Chain
Q= Co-enzyme Q
C= Cytochrome C
I,II,II,IV= protein complexes
Complex I takes electrons from NADH
Complex II takes electrons from FADH
Complex I and II transport these electrons to coenzyme Q
Reduced molecules of coenzyme Q are now floating about in the membrane and are used as substrates for complex III. Which uses electrons from coenzyme Q to reduce cytochrome C
Cytochrome C is loosely associated with the outer surface of the inner mitochondrial membrane. Passes electrons onto complex IV which then goes on to reduce oxygen along with the help of some protons from the matrix
Most of these electron transfer reactions are exothermic (complex I, II, IV) and are used to pump H+ ions across the inner mitochondrial membrane, out of the matrix and effectively into the cytosol.
Reduction potentials
+ve E 0 means:
- The ox’ed compound has a high potential to get reduced.
- Reduction of the ox’ed compound is a relatively spontaneous.
- Reduction of the ox’ed compound is an exothermic process that can drive endothermic processes.
Example;
Hydrogen carrier. Individual redox potential.
Electron carriers. Iron ions in complex with sulphur atoms. Only donate or accept one electron at a time. Structure varies. Range of reduction potentials.
Electron carriers. Proteins that are complexed with heme groups with an iron ion at the centre. Structure varies. Range of reduction potentials.
More in depth detail on the complexes
- Complex I is carrying out a reaction that transfers electrons from NADH to coenzyme Q. This process is coupled to the pumping of 4 protons (H+) out of the matrix. Coenzyme is reduced, forming QH2.
-
Takes cytochrome C and uses them to reduce oxygen. In that process 2 protons are pumped out of the matrix and 2 protons are used by oxygen to become water.
Final lecture on oxidative phosphorylation
ATP synthase- complex made of multiple subunits (very large).
Part of ATP synthase is embedded within the inner mitochondrial membrane and then part of it protrudes into the matrix.
The beta units are the ones that actually bind to ADP and phosphate. There are 3 of these beta subunits capable of doing this. These beta subunits are held in place by other subunits and also interact with the gamma stork. The gamma stork is a subunit that is capable of turning. When it turns it changes the conformation of the beta subunits and helps them to go through the shape changes necessary to combine ADP and phosphate to produce ATP
There are 3 beta subunits. As the gamma stork turns, it interacts with each of them differently, meaning there are 3 different conformations that each of these beta subunits can take. These are called loose, tight, and open. They all go through these states. Tight open loose.
When the beta unit is in the open conformation, it is able to reversibly bind and therefore release ATP or ADP and Pi. So, it usually releases ATP and then binds to ADP and Pi.
In the loose state, the beta subunits are able to bind and hold ADP and Pi.
In the tight state, the active site is perfectly shaped for ATP. It cannot, however, release the ATP.
ATP synthase summary
Because ATP synthase has 3 catalytic sites (the three beta subunits), one full rotation of the C ring means that 3 ATP molecules are made.
Human ATP synthase has 10 C subunits in the C ring... so the re-entry of 10 protons into the matrix... results in the synthesis of 3 molecules of ATP
In practice, the system is not 100% efficient, so for every NADH (which reduces one O atom), 2 ATP are produced. This is NADH’s P:O ratio.
For FADH2, the P:O ratio is 1.
Summary
Oxidative phosphorylation in mitochondria produces most of the ATP of metabolism.
The NADH of glycolysis is oxidised in shuttles, and its reducing power is transferred to the matrix.
The electron transport chain links exothermic transfer of electrons to the endothermic pumping of protons against their gradient.
The increasing reduction potentials of the complexes means the electron transfer is exothermic.
ATP synthase is a molecular motor, fuelled by the re-entry of protons, that rotates, driving ATP synthesis.
Electron transport chain
Module: Mammalian Physiology (PHOL0001)
University: University College London
- Discover more from: