BC368 Biochemistry of the Cell II Oxidative Phosphorylation

BC368 Biochemistry of the Cell II Oxidative Phosphorylation

BC368 Biochemistry of the Cell II Oxidative Phosphorylation CH 19 (pp 731-768) March 31, 2015 Oxidative phosphorylation is the coupling of energy release

during electron transport to ATP synthesis. "Anyone who is not confused about oxidative phosphorylation just doesn't understand the situation." -Efraim Racker 1913-1991 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

Fig 19-34 Uncouplers Thermogenin dissipates the proton gradient no work is done.

Huffington Post Fig 19-34 Uncouplers 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 1960s, 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 subunit has a different conformation:

-ADPADP -ADPATP -ADPempty Fig 19-26 ATP Synthase: The Binding Change Mechanism 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 Animation: Binding

Change Mechanism 4. Conformation changes back to initial state so that cycle continues

Fig 19-26 ATP Synthase: The Binding Change Mechanism ATP Synthase ATP Synthase: Rotation of Fo via the c Ring Each c subunit has two halfchannels, 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. Animation: start at :23

Energy balance sheet Mitochondrial shuttles Functionally, transport of OH- out is the same as transport of H+ in. Pmf-ADPdriven transport

Fig 19-30 Malate-ADPAsp shuttle Liver, kidney, and heart Results in NADH in the matrix

Complicated, but free! Fig 19-31 Malate-ADPAsp shuttle Liver, kidney, and heart Results in NADH in the

matrix Complicated, but free! Fig 19-31 Glycerol 3-ADPP shuttle Skeletal muscle and brain

Electrons enter at Q. Easier, but costly! Regulation Acceptor Control Fig 19-20

Regulation Coordinated Control Fig 19-35 In-ADPClass 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). (bacteria or hypoxia) makes The protein IF1 protects the cell from hypoxia-induced ATP hydrolysis.

Hypoxia IF1 inhibitor (a dimer at low pH) Inhibition of ATPase by IF1 Fig 19-33

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 yaxis is [O2]; isolated mitochondria; succinate is the electron source) Inhibitor Function

FCCP proton ionophore Malonate prevents oxidation of succinate Cyanide

inhibits electron transport Atractylate inhibits the ADP-ATP translocase Oligomycin

inhibits the ATP synthase Butylmalonate blocks the uptake of succinate by mitochondria

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