Download RESPIRATION: SYNTHESIS OF ATP

RESPIRATION: SYNTHESIS OF ATP
Respiration is a series
of coupled reactions
• Carbon (in glucose) is
oxidized
• ATP is formed from
ADP plus phosphate
O2
ADP + Pi
CO2 + H2O
ATP
What happens to the respiration in animal or plant cells in the
absence 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 NADH
to allow continued glycolysis, citric acid cycle
operation.
! 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 produces
lactic acid
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.
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 from
carrier to carrier in a specific order
FAD
FAD
Succinic
acid
Fumaric
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.
Electron transport chain: H+ moves from inside to
outside of membrane
FAD
FAD
Succinic
acid
Fumaric
acid
ATP synthetase: H+ moves back to the inside
through 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
(Fig. 7.15)
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
Rate control:
Should respiration run
at the same rate whatever
the demand for energy?
Homeostasis: rate of
respiration (fermentation)
controlled by level of ATP
Allosteric enzyme:
phophofructokinase
inhibited 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
Methanogenesis
4H2 + CO2 --> CH4 + 2 H2O
∆Go = -131 kcal/mol
∆G depends also on concentrations. This reaction
works if H2 and CO2 concentrations are high.
H+
e-
H2
ATP
CO2
CH4
H2O
H+