oxidative phosphorylation ch 19 (pp 731-768) march 31, 2015 bc368biochemistry of the cell ii
TRANSCRIPT
Oxidative Phosphorylation
CH 19 (pp 731-768)
March 31, 2015
BC368 Biochemistry of the Cell II
"Anyone who is not confused about oxidative phosphorylation just doesn't understand the situation."
-Efraim Racker
1913-1991
Oxidative phosphorylation is the coupling of energy release during electron transport to ATP synthesis.
Chemiosmotic Theory
Fig 19-19
Proton Motive Force
Fig 19-17= -
Case Study
In 1933, Stanford biochemists Cutting and Tainter published a report in the Journal of the American Medical Association on the use of dinitrophenol (DNP) to treat obesity. After its first year on the market, an estimated 100,000 people had been treated with DNP in the United States, in addition to many others abroad. Unfortunately, in some cases the treatment eliminated not only the fat, but also the patient.
How does DNP work as a diet pill, and what side effects would you expect?
Fig 19-21
Uncouplers
Fig 19-20
UncouplersFig 19-34
Thermogenin dissipates the proton gradient…no work is done.
Huffington Post
UncouplersFig 19-34
Other ways to waste energy
Bypassing the proton pumps leads to production of heat instead of ATP
Chemiosmotic Theory
Fig 19-19
Mechanism of ATP Synthesis
https://www.youtube.com/watch?v=PjdPTY1wHdQ
ATP Synthase: Fo and F1
In the 1960’s, “lollipop” structures were evident through electron microscopy in samples of everted inner membranes from bovine mitochondria.
ATP Synthase: Fo and F1
Matrix side
Matrix side
ATP Synthase: Kinetics
Fig 19-24
ATP Synthase: The Binding Change Mechanism
Each β subunit has a different conformation: β-ADPβ-ATPβ-empty
Fig 19-26
1. ADP and Pi bind
Fig 19-26
ATP Synthase: The Binding Change Mechanism
2. Conformation changes, catalyzing ATP formation; energy provided by H+ movement Fig 19-26
ATP Synthase: The Binding Change Mechanism
3. Conformation changes; ATP dissociates; energy provided by H+ movement
Fig 19-26
ATP Synthase: The Binding Change Mechanism
4. Conformation changes back to initial state so that cycle continues
Fig 19-26
ATP Synthase: The Binding Change Mechanism
Animation: Binding Change Mechanism
ATP Synthase
ATP Synthase: The Binding Change Mechanism
Animation: start at :23
ATP Synthase: Rotation of Fo via the c Ring
• Each c subunit has two half-channels, open to either the intermembrane space or to the matrix, that allow protons to access a key Asp residue.
• Protonation of the Asp relieves the negative charge and allows rotation into the membrane.
• Rotation of negative Asp out of the membrane results in deprotonation.
Energy balance sheet
Mitochondrial “shuttles”
Functionally, transport of OH- out is the same as transport of H+ in.
Pmf-driven transport
Fig 19-30
Malate-Asp shuttle
Liver, kidney, and heart
Results in NADH in the matrix
Fig 19-31
Complicated, but free!
Malate-Asp shuttle
Complicated, but free!
Liver, kidney, and heart
Results in NADH in the matrix
Fig 19-31
Glycerol 3-P shuttle
Electrons enter at Q.
Skeletal muscle and brain
Easier, but costly!
Regulation
Acceptor Control
Fig 19-20
Regulation
Coordinated Control Fig 19-35
In-Class Problem
The mitochondria of a patient oxidize NADH irrespective of whether ADP is present. The P:O ratio (ATP synthesized per oxygen atom [or pair of electrons] consumed) for oxidative phosphorylation by these mitochondria is less than normal. Predict the likely symptoms of this disorder.
Hypoxia
Normally, the ATP synthase makes ATP, using the proton gradient
Sometimes, the ATP synthase uses ATP to generate a proton gradient (acts as a ATPase).
makes(bacteria or hypoxia)
IF1 inhibitor (a dimer at low pH)
Hypoxia
Inhibition of ATPase by IF1 Fig 19-33
The protein IF1 protects the cell from hypoxia-induced ATP hydrolysis.
Hypoxia
When O2 is limiting, electrons may fall out of the electron transport chain, often at Q−.
Hypoxia
When O2 is limiting, electrons may fall out of the electron transport chain, often at Q−.
Superoxide dismutase converts O2
− to H2O2.
Glutathione peroxidase breaks down the H2O2.
Hypoxia
Other protective effects are mediated by HIF-1:
Decreased activity of PDH (via the kinase).
Swapping out of a complex IV subunit.
Assign each inhibitor to one of the oxygen traces on the right (the y-axis is [O2]; isolated mitochondria;succinate is the electron source)