RESPIRATION: SYNTHESIS OF ATP. Clickers!

Transcription

1 RESPIRATION: SYNTHESIS OF ATP Clickers!

2 Respiration is a series of coupled reactions Carbon (in glucose) is oxidized ATP is formed from ADP plus phosphate O 2 ADP + Pi CO 2 + H 2 O ATP

3 Synthesis of ATP Anaerobic conditions (fermentation)! Glycolysis depends on a supply of substrates: glucose, ATP, ADP, Pi, NAD+! NAD+, FAD present in only small amounts in cell, and NAD+ and FAD are used up in glycolysis and the citric acid cycle.! Therefore, NAD+ must be regenerated from NADH to allow continued glycolysis, citric acid cycle operation.! In air, the electron transport chain regenerates NAD+ and FAD by passing electrons to O2.! Without air, the electron transport chain cannot oxidize NADH, FADH2; citric acid cycle stops.! Without air, some cells regenerate NAD+ (from glycolysis only) by passing e- (+ H+) to pyruvic acid! Result: continued glycolysis, forming 2 ATP per glucose

4 Muscle cells Reduction of pyruvate produces lactic acid

5 Yeast cells Reduction of pyruvate produces ethanol Variations:! Most plants make EtOH, but are hurt by large amounts; some plants make lactic or malic acid and tolerate these better.! Most animals make lactic acid, but the acid hurts; goldfish make EtOH and excrete it.

6 Synthesis of ATP Aerobic conditions: electron transport chain! Electron carriers (4 protein complexes) positioned close together in the membranes of the cristae; FAD, heme are associated with proteins (enzymes) that facilitate transfer of electrons; Q floats in lipid bilayer.! Carriers have increasing affinity for electrons; thus, electrons move from carrier to carrier in a specific order.

7 Electron transport chain: electrons move from carrier to carrier in a specific order FAD Succinic acid FAD Fumaric acid

8 Synthesis of ATP Aerobic conditions: electron transport chain! Electron carriers (4 protein complexes) positioned close together in the membranes of the cristae; FAD, heme are associated with proteins (enzymes) that facilitate transfer of electrons; Q floats in lipid bilayer.! Carriers have increasing affinity for electrons; thus, electrons move from carrier to carrier in a specific order.! Carriers are positioned in cristae so that H+ moves from inside to outside of membrane as electrons move from NADH to O2.! H+ moves back to the inside through an enzyme --ATP synthetase--that forms ATP + H2O from ADP + Pi.

9 Electron transport chain: H+ moves from inside to outside of membrane FAD FAD Succinic acid Fumaric acid

10 ATP synthetase: H+ moves back to the inside through an enzyme that forms ATP + H2O from ADP + Pi.

11 ATP synthetase: Adding ATP to the enzyme pumps H+ through the membrane (running backwards relative to ATP synthesis). It also makes the center protein rotate. The ATP synthetase is a rotary pump! (Running forward, it is a turbine.)

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13 Calculating the ATP yield of respiration of one glucose molecule Glycolysis Pyruvate oxidation Citric acid cycle +2 NADH +2 ATP +2 NADH +2 ATP (GTP) +6 NADH +2 FADH 2 (Fig. 9.13) Electron transport chain -2 NADH +4 ATP -8 NADH +24 ATP -2 FADH 2+4 ATP +36 ATP

14 Rate control: Should respiration run at the same rate whatever the demand for energy? Homeostasis: rate of respiration (fermentation) is controlled by level of ATP Allosteric enzyme: Phophofructokinase is inhibited by ATP and Citrate (see Fig. 9.16)

15 Summary: how free energy flows through the cell! Cells get free energy in the form of glucose (or other organic molecules)! Oxidation of glucose releases free energy; much is saved as reduced NADH and FADH2 (and a little ATP) are formed in coupled reactions; the rest lost as heat! Oxidation of NADH and FADH2 releases free energy; much is saved as electrochemical (H + ) gradient; the rest lost as heat! Reversal of electrochemical gradient (H + transport) releases free energy; much is saved as ATP; the rest lost as heat! Hydrolysis of ATP releases free energy; some is saved (in energy of position, new chemical gradients from transport of compounds across membranes, synthesis of polymers, etc.); the rest lost as heat.

16 How did primeval organisms respire?

17 Methanogens may have been early life forms Methanogenesis 4H 2 + CO 2 --> CH H 2 O G o = -131 kcal/mol G depends also on concentrations. This reaction works if H 2 and CO 2 concentrations are high. H + CO 2 e - H 2 ATP CH 4 H 2 O H +