Oxidative Phosphorylation

Question 1

Chemiosmotic theory

Answer 1

the concept that a proton concentration gradient serves as the energy reservoir that drives ATP formation.

Question 2

Complex I

Answer 2

• NADH dehydrogenase
• carriers transmit the two e- from NADH and deliver to Q (ubiquinone) to make QH2 (ubiquinol).
• QH2 is lipid soluble and diffuses through the membrane to complex III
• reactant: NADH, Q
• Product: NAD+, QH2
• 4 H+ pumped out

Question 3

Complex II

Answer 3

• succinate dehydrogenase
• accepts electrons from succinate and catalyzes the reduction of Q to QH2
• electron carriers are FAD then 3 Fe-S centers before the two electrons are used for Q reduction
• no H+ translocated but serves as as tributary that supplies electrons (as QH2) to the rest of ETC
• reactant: succinate, Q
• product: fumarate, QH2
• no H+ pumped out

Question 4

Complex III

Answer 4

• cytochrome bc1 complex
• electron transport coupled to Q cycle
• subunits in electron transport at cytochrome b subunit, Rieske iron sulfur protein, and cytochrome c subunit
• reactant: QH2, cytc (ox)
• product: Q, ctyc (red)
• 4 H+ pumped out

Question 5

Q cycle

Answer 5

• Two e- passed separately from molecule of QH2 at Q0 site.
• one e- transferred to Fe-S cluster then to cytochrome c1, and finally to cytochrome c, the terminal carrier.
• the other e- transferred to heme bH then to Q to make semiquinone radical. second e- forms QH2
• 4 H+ translocated

Question 6

Complex IV

Answer 6

• cytochrome c oxidase
• four cyt c (red) molecules bind sequentially and the electrons are transferred to the Cu center and accumulate there; these results in the splitting of the 1/2 O2 molecule and addition to 2 H+ to form H2O
• one H+ ion is translocated for each e- passed from cyt c to O2. pump out 2 H+
• reactant: cytc (red), 1/2 O2 + 2 H+
• product: cytc (ox), H2)
• 2 H+ pumped out

Question 7

Organization of ATP synthase (F0, F1 domains)

Answer 7

• Divided into integral transmembrane protein part named F0 and knobby part that sticks into mitochondrial matrix named F1
• F0 subunit forms a proton channel at the interface between the a and c subunits
• rotor - all subunits rotate together when protons move on at a time from P side to N side
• stator - all of this complex is fixed in the membrane and cannot rotate with the rotor

Question 8

Binding change mechanism

Answer 8

• The c subunit complex rotates in the membrane as H+ move from the P to the N side of the inner membrane
• the y subunit is asymmetric and as it rotates past a B subunit of each a B pair, it induces a change in the beta conformation
• depending of position of y subunit, the B subunit is sequentially in open, loose, and tight conformations
• open - dissociates ATP and allow association of ADP and Pi
• loose - ADP and Pi bound to react
• Tight - ATP bound
• 1 revolution to produce on ATP (takes 3 H+ but acts like 4 due to the adenine nucleotide transporter and the Pi transporter) transporting ATP out of matrix and Pi and ADP in

Question 9

significance of the NADH shuttles

Answer 9

• NADH generated during glycolysis cannot reach the ETC directly
• malate aspartate shuttle brings in complex I - NADH to 2.5 ATP - liver heart kidneys
• glycerol-3-phosphate brings into complex III - NADH to 1.5 ATP - brain and skeletal muscle

Question 10

Uncoupling of oxidative phosphorylation

Answer 10

• as a consequence of this uncoupling of ATP synthesis from respiration the free energy released from these reactions appears as heat.
• infants, hibernating animals express uncoupling protein