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Electron Transport Chain and Chemiosmosis. Introduction to the ETC. The electron carrying molecules, NADH and FADH 2 , transfer their electrons to a series of compounds (mostly proteins), which are associated with the cristae. How it Works.
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Introduction to the ETC • The electron carrying molecules, NADH and FADH2, transfer their electrons to a series of compounds (mostly proteins), which are associated with the cristae.
How it Works • The protein/compounds are arranged in order of increasing electronegativity… therefore each successive compound wants the electrons more than the one before it.
How it Works • The compounds: NADH dehydrogenase, ubiquinone (Q), the cytochrome b-c1 complex, cytochrome c, cytochrome oxidase complex.
How it Works • Each compound is reduced by gaining two electrons from the one before it and oxidized by donating its two electrons to the one after it.
How it Works • As the electrons are passed they become more stable and therefore generate free energy.
How it Works • This free energy is used to pump protons into the intermembrane space from the matrix (Active transport). There are three proton pumps. • Oxygen is the final electron acceptor and it joins with two protons in the matrix to form water.
Steps for NADH • NADH gives up its two electrons to NADH dehydrogenase.
Steps for NADH • The mobile carriers Q and cytochrome c shuttle electrons from one protein complex to the next until they reach the final protein complex, cytochrome oxidase. • Along the way, as the electrons lose energy and become more stable, 3 protons are actively transported from the matrix into the intermembrane space.
Steps for NADH • Here part of the cytochrome catalyzes the reaction between the electrons, protons and oxygen to form water.
Steps for NADH • This process is highly exergonic (giving up free energy 222kJ/mol)… the chemical potential energy of electron position is converted to electrochemical potential energy of a proton gradient that forms across the inner mitochondrial membrane. • This energy will be used to power ATP synthesis in chemiosmosis.
Electrochemical Gradient Intermembrane space Cristae Matrix
Path of FADH2 • FADH2 skips the first protein compound. This means that FADH2 oxidation pumps two protons into the intermembrane space. • Three ATP are formed from the electrons from NADH while only two ATP are formed from the electrons from ATP FADH2 as they begin with lower energy.
NADH from Glycolysis • Important to note that the NADH formed in glycolysis in the cytoplasm passes into the mitochondrial matrix through the glycerol-phosphate shuttle, where its electrons are passed to FADH2, therefore FADH2 essentially is created in glycolysis, therefore two ATP are formed from that electron carrying molecule.
NADH from Glycolysis • There is another way that NADH can pass its electrons to another NAD+ instead of FAD… it is the aspartate shuttle, but we will just assume this one does not exist. • There are many copies of the ETC along the cristae; therefore lots of ATP can be produced.
Chemiosmosis and Oxidative Phosphorylation • There is an electrochemical gradient across the cristae. (More protons outside than in the matrix) • Two parts: difference in charge and a difference in concentration.
Electrochemical Gradient Intermembrane space Cristae Matrix
Chemiosmosis and Oxidative Phosphorylation • The inner membrane is impermeable to protons. • The protons are forced through special proton channels that are coupled with ATP synthase (ATPase).
Chemiosmosis and Oxidative Phosphorylation • The electrochemical gradient produces a proton-motive force (PMF) that moves the protons through this ATPase complex.
Chemiosmosis and Oxidative Phosphorylation • Each time a proton comes through the ATPase complex, the free energy of the electrochemical gradient is reduced and this energy is used to create ATP from ADP + P in the matrix.
Chemiosmosis and Oxidative Phosphorylation It is about time! • Peter Mitchell found all this out in 1961 and coined the term chemiosmosis because the energy that drives ATP production comes from the osmosis of protons. It took a long time for his theory to be accepted. He finally got his Nobel Prize in 1978.
Chemiosmosis and Oxidative Phosphorylation • The continual production of ATP is dependent on the maintenance of a proton reservoir in the intermembrane space. This depends on the continued movement of electrons and that depends on the availability of oxygen. • Therefore we need oxygen to prevent the ETC from being clogged up and we need food to provide the glucose that provides electrons for the ETC.
