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Title: Oxidative phosphorylation explained
Description: These are very good summary notes for anyone pursuing a Bachelor's Degree in Biochemistry or Biology. I use these notes to lecture Biochemistry at the University of Zambia
Description: These are very good summary notes for anyone pursuing a Bachelor's Degree in Biochemistry or Biology. I use these notes to lecture Biochemistry at the University of Zambia
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OXIDATIVE
PHOSPHORYLATION
C
...
•Enzymes for this process are found in inner mitochondrial
membrane in eukaryotes
...
The respiratory electron-transport chain where NADH and FADH2
are oxidized and the released electrons pass through enzyme
complexes and electron carriers all the way to molecular oxygen
...
The matrix therefore
becomes relatively more alkaline and negatively charged
...
ATP synthesis
...
When H+ are moved
back across inner mitochondrial membrane through pores associated
with ATP synthase, ADP is phosphorylated to form ATP
...
• Unlike substrate level phosphorylation, it does not involve
phosphorylated chemical intermediates but a very different
mechanism was proposed by Peter Mitchell
CHEMIOSMOTIC HYPOTHESIS
...
• Thus the proton gradient couples electron transport and ATP
synthesis, not a chemical intermediate
...
Events in oxidative phosphorylation
• Electron transport down the respiratory chain from NADH
oxidation causes H+ ions to be pumped out of the mitochondrial
matrix across the inner mitochondrial membrane into the
intermembrane space by the three H+ pumps; NADH
dehydrogenase, the cytochrome bc1 complex and cytochrome
oxidase
...
4
Oxidative phosphorylation cont…
• The free energy change in transporting an electrically charged ion
across a membrane is related both to its electrical charge and the
concentration of the species
...
• The protons flow back into the mitochondrial matrix through the
ATP synthase and this drives ATP synthesis
...
e
...
e
...
6
Oxidative phosphorylation cont…
7
Coupling & Respiratory Control
• Electron transport is normally tightly coupled to ATP synthesis
• i
...
electrons do not flow through the electron transport chain to
oxygen unless ADP is simultaneously phosphorylated to ATP
...
• SO oxidative phosphorylation needs NADH or FADH2, oxygen,
ADP and inorganic phosphate
...
8
PURPOSE OF RESPIRATORY CONTROL
• This mechanism ensures that electrons flow down the chain
only when ATP synthesis is needed
...
9
Uncouplers OR Uncoupling agents-2,4-dinitrophenol (DNP)
• When added to cells, it stops ATP synthesis but electron transport
still continues and so oxygen is still consumed
...
• Electron transport occurs and pumps out H+ ions across the inner
mitochondrial membrane but DNP in the same membrane carries the
H+ ions back into the mitochondrion
...
Since no proton gradient forms, no ATP can be
made by oxidative phosphorylation
...
• The production of heat by uncoupling is called NONSHIVERING
10
THERMOGENESIS
...
• Occurs naturally in brown adipose tissue
...
• Thermogenin allows H+ ions to flow back into mitochondria
without having to enter via the ATP synthase and so uncouples
electron transport and oxidative phosphorylation, generating
heat
...
Reoxidation of cytosolic NADH
• Electrons from cytosolic NADH enter the mitochondria by
shuttles
• The inner mitochondrial membrane is impermeable to NADH
and so NADH produced in the cytoplasm during glycolysis must
be reoxidized via a membrane shuttle, a combination of
enzyme reactions that bypass this impermeability barrier
...
• The glycerol 3-phosphate diffuses across the inner
mitochondrial membrane where it is converted back to
dihydroxyacetone phosphate by mitochondrial glycerol 312
phosphate dehydrogenase
Reoxidation of cytosolic NADH
• The dihydroxyacetone phosphate then diffuses back to the
cytosol
...
• The enzyme-linked FADH2 (E
...
Note
• The shuttle does not allow cytoplasmic NADH to enter the
mitochondrion but its operation effectively transports the two
electrons from the NADH into the mitochondrion and feeds
them into the electron transport chain
...
• The malate enters the mitochondrion via a malate–αketoglutarate carrier in the inner mitochondrial membrane
...
• Oxaloacetate does not easily cross the inner mitochondrial
membrane and so is transaminated to form aspartate which
then exits from the mitochondrion
15
MALATE–ASPARTATE SHUTTLE
cont…
...
• The net result of this cycle of reactions is to transfer the
electrons from NADH in the cytosol to NADH in the
mitochondrial matrix which is then reoxidized by the electron
transport chain
...
17
SUMMARY
18
Title: Oxidative phosphorylation explained
Description: These are very good summary notes for anyone pursuing a Bachelor's Degree in Biochemistry or Biology. I use these notes to lecture Biochemistry at the University of Zambia
Description: These are very good summary notes for anyone pursuing a Bachelor's Degree in Biochemistry or Biology. I use these notes to lecture Biochemistry at the University of Zambia