Proton path through the membrane Each proton enters

• Proton path through the membrane: Each proton enters cytosolic half-channel, follows a complete rotaion of c ring, and exit through the other half-channel into the matrix.

Many shuttles allow movement across the mitochondrial membranes Electrons from cytosolic NADH enter mitochondria by shuttles

• Glycerol 3 -phosphate shuttle: e from NADH can enter mitochondrial e transport chain by being used to reduce dihydroxyacetone phosphate to glycerol 3 -phosphate. Glycerol 3 -phosphate is reoxidized by e transfer to FAD in membrane-bound glycerol 3 -phosphate dehydrogenase. Subsequent e transfer to Q to form QH 2 allows e to enter e transport chain.

• 1. 5 rather than 2. 5 ATP are formed when cytosolic NADH transported by the glycerol phosphate shuttle is oxidized by the respiratory chain.

The Entry of ATP into Mitochondria is Coupled to the Exit of ATP by the ATP-ADP Translocase Mitochondrial ATP-ADP translocase: Translocase catalyzes the coupled entry of ADP and exit of ATP from matrix. The reaction cycle is driven by membrane potential. The actual conformational change corresponding to eversion of binding site could be quite small.

• ATP-ADP translocase: Adenine nucleotide carrier. • ADP enters the mitochondrial matrix only if ATP exits, and vice versa. • In the presence of a positive membrane potential, the rate of binding-site eversion from the matrix to the cytosolic side is more rapid for ATP than for ADP because ATP has one more negative charge. • The membrane potential is decreased by the exchange of ATP for ADP, which results in a net transfer of one negative charge out of the matrix.

The regulation of cellular respiration is converted primarily by the need for ATP The Complete Oxidation of Glucose Yields About 30 ATP are formed when glucose is completely oxidized to CO 2.

The Rate of Oxidative Phosphorylation is Determined by the Need for ATP • electron transport tightly coupled to phosphorylation: Electrons do not usually flow through the electron transport chain to O 2 unless ADP is simultaneously phosphorylated to ATP. • Level of ADP: the most important factor to determine rate of oxidative phosphorylation

• Respiratory control: e are tranferred to O 2 only if ADP is concomitantly phosphorylated to ATP.

Oxidative phosphorylation can be inhibited at many stages • 1) e-transporter inhibitor • Rotenone/ Amytal. • Antimycin. • Cyanide/ azide/ carbon monoxide • 2) ATP synthase inhibitor • ATP synthase can be inhibited by oligomycin and DCCD.

• 3) uncoupler: This tight coupling of electron transport and phosphorylation in mitochondria can be disrupted by 2, 4 -dinitrophenol and certain other acidic aromatic compounds. These substances carry protons across the inner mitochondrial membrane. • 4) ATP export: ATP-ADP translocase inhibited by atractyloside, bongkrekic acid

Regulated uncoupling leads to the generation of heat • The uncoupling of oxidative phosphorylation is a means of generating heat to maintain body temperature in hibernating animals, in some newborn animals, and in mammals adapted to cold. • brown adipose tissue: specialized for nonshivering thermogenesis • UCP-1 (thermogenin): uncoupling protein in inner mitochondrial membrane • UCP-1 generates heat by short-circuiting the mitochondrial proton battery.

• action of UCP: UCP-1 generates heat by permitting the influx of protons into the mitochondria without synthesis of ATP.

Mitochondria play a key role in apoptosis • Programmed cell death/ apoptosis • activation of caspase: destroy of cell structure • degradation of protein that inhibits an enzyme that destroys DNA

Power Transmission by Proton Gradients: A Central Motif of Bioenergetics * Proton gradients are a central interconvertible currency of free energy in biological systems.