Electron Transport and Chemiosmosis Stage 4 of cellular respiration

The Electron transport chain (ETC) A series of protien complexes in the inner mitrochondrial membrane. Each mitochondria has many Complexes are organized in order of increasing electronegativity: weakest attraction for electrons first and strongest attraction at the end Electrons shuttle through it like a baton in a relay

The components of the ETC in order of increasing electronegativity are: NADH dehydrogenase complex, ubiquinone (Q), the cytochrome b-c 1 complex, cytochrome c (cyt c) and the cytochrome c oxidase complex. Q and cyt c are carriers From:

What happens? NADH and FADH 2 (made in stages 1-3) each transfer 2 electrons to the ETC Free energy is released by the electrons as they travel through the chain and is used to pump one proton per complex into the intermembrane space. This creates an electrochemical gradient across the intermembrane space (like a battery) Once the electrons reach the last protein in the ETC, they are very stable, so a HIGHLY electronegative substance (OXYGEN) is used to remove them. (final electron acceptor) The attachment of these electrons to the oxygen attracts protons, forming water

PROCESS: 1.NADH gives up 2 electrons to NADH dehydrogenase 2.Q shuttles the electrons to cytochome b-c 1 complex 3.cytochrome shuttles the electrons to cytochrome oxidase complex 4.Cytochrome oxidase catalyzes the reaction between the electrons, free protons and oxygen to make water

NADH vs FADH 2 NADH will transfer electrons to the first protein complex (NADH dehydrogenase) in the ETC and so pumps 3 hydrogens per molecule FADH 2 transfers its electrons to Q (the second protein in the ETC) and so pumps 2 hydrogens per molecule

Cytosolic vs mitrochondrial NADH The inner mitochondrial membrane is impermeable to NADH So…NADH created in glycolysis must be shuttled via a transport protein into the matrix. In doing so, it becomes FADH 2.

Chemiosmosis The electrochemical gradient generated during electron transport stores free energy (called proton-motive force PMF) Inner mitochondrial membrane is impermeable to H+ ions PMF forces protons through ATP synthase and the energy from this drives the systhesis of ATP from ADP and inorganic phosphate in the matrix One ATP is generated per proton pumped into the intermembrane space.

After ATP is made, it is transferred through the mitochondrial membrane by facilitated diffusion into the cytoplasm so it can do things like active transport

Interesting: In order for ATP to continue to be produced, an H+ reservoir must be maintained. This means electrons must be continually moving through the ETC To keep the electrons moving, oxygen must be present to accept them at the end of the chain Without food, there would be no electrons (this is why we must continually eat) If there is no oxygen, electrons will not be able to flow through the ETC and it will become “clogged” with electrons. H+ ions will no longer be pumped into the intermembrane space and chemiosmosis stops, ATP synthase stops and NADH/FADH 2 are no longer able to give up electrons and can’t be recycled… organism will die due to lack of ATP if oxygen is withheld for too long.