4. oxidative phosphorylation
TRANSCRIPT
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
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
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
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