Electron Transport Chain and Chemiosmosis

Introduction to the ETCThe electron

carrying molecules, NADH and FADH2, transfer their electrons to a series of compounds (mostly proteins), which are associated with the cristae.

How it WorksThe

protein/compounds are arranged in order of increasing electronegativity… therefore each successive compound wants the electrons more than the one before it.

How it WorksThe compounds: NADH dehydrogenase,

ubiquinone (Q), the cytochrome b-c1 complex, cytochrome c, cytochrome oxidase complex.

How it WorksEach 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 WorksAs the electrons are passed they become

more stable and therefore generate free energy.

How it WorksThis 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 NADHNADH gives up its two electrons to NADH

dehydrogenase.

Steps for NADHThe 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 NADHHere part of the cytochrome catalyzes the

reaction between the electrons, protons and oxygen to form water.

Steps for NADHThis 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 GradientIntermembra

ne space

Matrix

Cristae

Path of FADH2FADH2 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 GlycolysisImportant 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 GlycolysisThere 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 GradientIntermembra

ne space

Matrix

Cristae

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

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.

It is about time!

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.

REVIEW THIS!!!