Electron Transport Chain and Chemiosmosis

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. (don’t need to know names)

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.

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.

Chemiosmosis and Oxidative Phosphorylation There is an electrochemical gradient across the cristae. (More protons in the intermembrane space 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.

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