RESPIRATION: SYNTHESIS OF ATP

Respiration is a series of coupled reactions • Carbon (in glucose) is oxidized

• ATP is formed from ADP plus phosphate

O2 CO2 + H2O

ADP + Pi ATP

What happens to the respiration in animal or plant cells in theabsence of oxygen?

(a) Everything stops!(b) Glycolysis stops(c) Pyruvic acid oxidation and the citric acid cycle stop(d) The electron transport chain runs backward(e) Everything except the electron transport chain works as

well as in the presence of oxygen

Synthesis of ATP

Anaerobic conditions (fermentation)

! Glycolysis depends on a supply of substrates:

glucose, ADP, Pi, NAD+

! NAD+, FAD present in only small amounts in cell.

! Therefore, NAD+ must be regenerated from NADHto allow continued glycolysis, citric acid cycleoperation.

! In air, electron transport chain regenerates NAD+

and FAD by passing electrons to O2.! Without air, 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

Muscle cells

Reduction of pyruvate produceslactic acid

Yeast cells

Reduction of pyruvate producesethanol

Variations:! Most plants make EtOH, but are

hurt by large amounts; someplants make lactic or malic acidand tolerate these better.

! Most animals make lactic acid,but the acid hurts; goldfish makeEtOH and excrete it.

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.

Electron transport chain: electrons move fromcarrier to carrier in a specific order

FADFADSuccinic

acidFumaric

acid

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.

Succinic acid Fumaric

acid

FADFAD

Electron transport chain: H+ moves from inside to

outside of membrane

ATP synthetase: H+ moves back to the insidethrough an enzyme that forms ATP + H2O from

ADP + Pi.

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.)

Calculating the ATP yield of respiration

Glycolysis +2 NADH+2 ATP

Pyruvate oxidation +2 NADH

Citric acid cycle +2 ATP (GTP)+6 NADH+2 FADH2

Electron transport chain -2 NADH+4 ATP

-8 NADH+24 ATP

-2 FADH2+4 ATP+36 ATP(Fig. 7.15)

Rate control:

Should respiration runat the same rate whateverthe demand for energy?

Homeostasis: rate of respiration (fermentation)controlled by level of ATP

Allosteric enzyme: phophofructokinaseinhibited by ATP and citrate

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 saved as electrochemical (H+)

gradient; the rest lost as heat

! Reversal of electrochemical gradient (H+

transport) releases free energy; much saved as ATP; the rest lost as heat

! Hydrolysis of ATP releases free energy; some saved (in energy of position, new chemical gradients from transport of compounds across membranes, synthesis of polymers, etc.); the rest lost as heat.

How did primeval organisms respire?

How did primeval organisms respire?

How did primeval organisms respire?(a) Oxidation of glucose, just as in the present(b) oxidation of methane (CH4)(c) reduction of methane(d) reduction of carbon dioxide (CO2)(e) oxidation of carbon dioxide

Methanogens may have been early life forms

Methanogenesis4H2 + CO2 --> CH4 + 2 H2O ∆Go = -131 kcal/mol

∆G depends also on concentrations. This reactionworks if H2 and CO2 concentrations are high.

H2

H+ CO2

CH4

H2O

H+

ATP

e-