respiration : synthesis of atp - · electron carriers (4 protein complexes) positioned close...
TRANSCRIPT
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
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: 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?(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