Oxidative Phosphorylation

Oxidative Phosphorylation

This occurs in the inner membranes of the mitochondriaenzymes and protein carrier molecules embeddedfolded into cristae to increase the surface area

NAD reduced and FAD reduced are passed to ETCThe Hydrogen atom is split into a proton (H+) and an electron (e-)

The proton remains in solution

The molecule that splits hydrogen moves the proton into the inter-membrane space

The proton will later be used to reduce oxygen

The electron is transferred to various electron carriers along a biological electron transport chain

At certain points ATP is made by phosphorylation – during chemiosmosis

Oxygen is finally reduced to water

Biological electron transport This is a series of linked oxidation and reduction, or Redox, reactionsa donor and an acceptor of electrons

The acceptor gains an electron and becomes reduced

The donor looses an electron and becomes oxidized

Fe2+ + Cu2+ Fe 3+ + Cu+

Energy is lost as the electron is passed along the chainusually as heat

At certain points there is enough energy to make ATP

This is done by a process called Chemiosmosis

In the first step NADreduced donates the hydrogen to a hydrogen carrierThe first hydrogen carrier is now in the reduced state

The hydrogen is then passed to a second hydrogen carrier moleculeThis is now reducedThe first carrier is oxidisedIt can now pick up more hydrogen

It is at this point that FAD can first donate hydrogen If FAD is being used the process begins here

The hydrogen is broken into a proton and an electronThe proton is released into the inter-membrane space because of the structure of the carrier moleculeThis will make a proton gradient across the inner membrane

An electron acceptor molecule picks up the electron and becomes reduced

The electron is passed to a second electron carrier then to Cytochrome oxidase – which is now reduced

The final electron acceptor is oxygenTwo electrons combine with a 2 protons to form 2 hydrogensThese are picked up by oxygen, forming water

The final step in oxidative phosphorylation involves cytochrome oxidase reducing oxygen to water.

This step can be inhibited using Potassium Cyanide or Carbon monoxide

These are known as respiratory inhibitorsthey can be used experimentally to show the effects of blocking respiration (energy release) on a process

The transfer of electrons makes energy availableSome is lost as heatBut at some points there is enough energy released to produce ATP

Potentially each NADreduced can generate 3 ATP moleculesAnd each NADreduced can generate 2 ATP molecules

In reality 25% of the energy made is used in transporting ATP out of the mitochondria

thereforeFor each NAD reduced there are 2.5 ATP made

For each FAD reduced there are 1.5 ATP made

process NAD reduced

made

FAD red

made

Amount ATP

formed in ETC

Total

glycolysis 2 - 2 x 2.5 = 5

Link reaction

1x2 - 2 x 2.5= 5

Krebs Cycle

3x2

1 x 2

6 x 2.5 =

3 x 1.5 =

15

3

TOTAL 28

Process ATP/glucose

glycolysis -2 + 4 = 2

Link reaction -

Krebs cycle 1 x 2 = 2

Oxidative phosphorylation

28

TOTAL 32

Chemiosmosis

the most accepted explanation for ATP synthesis during the electron transport chain

Note that ATP formed in glycolysis and the Krebs cycle uses Chemical Potential energy from the bonds

Energy from the ETC is used to pump hydrogen ions

from the mitochondrial matrix to the space between the membranes of the envelope

This occurs because of the orientation of the proteins that pick up and then loose the hydrogen ionsthey will always transfer the ions to one side of the membrane

There are “stalked particles” that cross the inner membrane and act as both channels for the H+ ions to diffuse down their gradient,And as ATPsynthase molecules

For 3 H+ ions moving through the ATPsynthase one ADP is phosphorylated to ATP

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