Download VI. Reaction Coupling and ATP

VI. Reaction Coupling and ATP [cont.]
The ATP cycle
ATP
Phosphorylation
Strongly
Endergonic
Energy from
exergonic
reactions
ADP+ P
Hydrolysis
Strongly
Exergonic
Energy for
endergonic
reactions
VII. Metabolism
Background:
•
•
•
•
Metabolism of a cell = Sum of all chemical reactions in cell
Chemical reactions linked in metabolic pathways
Cells couple exergonic and endergonic reactions
Cells regulate chemical rxns through enzymes
Cells regulate enzyme activity (to regulate reactions)
1. Regulate synthesis
• synthesize enzyme only when
product needed
2. Regulate active state
• synthesize in inactive state
• activate when needed
3. Noncompetitive Inhibition (Allosteric)
• molecule binds to “other” site
• changes active site shape
4. Competitive inhibition
• molecule binds to active site
• prevents substrate binding
Cells regulate enzyme activity (to regulate reactions)
Feedback inhibition
- Works on complex, pathway reactions
- Final product “feeds back” and inhibits
early enzyme in pathway
I. Cellular Energy Harvest: an Overview
Energy to Drive Metabolism:
•
•
Autotrophs – use inorganic sources of energy
Photoautotrophs
–
–
•
harvest sunlight
convert radiant energy into chemical energy.
Heterotrophs – use organic sources of energy
–
–
live off the energy produced by autotrophs.
extract energy from food catabolism
Overview: Energy
Harvest
Overview: How is Glucose metabolized?
The reaction (if glucose is used to full potential)
Loss of hydrogen
atoms (oxidation)
C6H12O6 + 6O2 --> 6CO2 + 6H2O + ATP & Heat
Gain of hydrogen
atoms (reduction)
Cellular respiration oxidizes food molecules!
Overview: How is Glucose metabolized?
Step #1 Glycolysis:
In cytoplasm
Glucose
2 pyruvate
(Yields a little Energy)
Aerobic conditions:
#2 Cellular respiration:
In mitochondria
Lots of ATP
CO2 + H2O
Anaerobic conditions:
#2 Anaerobic respiration
or
#2 Fermentation
In cytoplasm
To Lactate or Ethanol
2 ATP, No high energy e-
Releasing Energy from Glucose
! Harvesting energy:
– cells break chemical bonds
– shift electrons from molecule to molecule.
! Where do the electrons go?
– Aerobic respiration
• final electron acceptor is Oxygen
– Anaerobic respiration
• final electron acceptor is not oxygen, but is an
inorganic molecule (e.g. CO2, SO4)
– Fermentation
• final electron acceptor is an organic molecule
II. Stages of Aerobic Cellular Respiration
Overview
Cytoplasm
A. Glycolysis
Glucose
B. Pyruvate oxidation
C. Krebs (Citric Acid) Cycle
NADH
Glycolysis
ATP
D. Electron Transport Chain
Pyruvate
Pyruvate
oxidation
NADH
AcetylCoA
NADH
Krebs
cycle
Intermembrane
space
CO2
Mitochondrial matrix
CO2
ATP
FADH2
H2O
ATP
NAD+ and FAD
eMitochondrion
Electron
transport chain
Inner mitochondrial membrane
A. Glycolysis:
1
2
6-carbon glucose
(Starting material)
2 ATP
P
3
P
P
6-carbon sugar diphosphate
P
6-carbon sugar diphosphate
P
P
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
3-carbon sugar 3-carbon sugar
phosphate
phosphate
NADH
NADH
2 ATP
2 ATP
3-carbon
pyruvate
Priming reactionsEnergy investment.
Cleavage reactions.
P
3-carbon
pyruvate
Energy-harvesting
reactions.
Transferring Energy: Reduction of NAD+
Oxidation: Dehydrogenase removes electrons from substrate
Reduction: Electrons in Hydrogen Transferred to NAD+
H
O
H
Oxidation
Dehydrogenase
O + 2H
(Enzyme)
+
NAD
+ 2H
Reduction
!
2H+ + 2e
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
+
NADH + H
(carries
2 electrons)
Substrate-Level Phosphorylation
High energy phosphate bond is transferred enzymatically to ADP
A. Glycolysis: Summary
! Catabolic pathway with 3 major events:
1. Priming (Energy Investment)
2. Cleavage (6-C to 2X 3-C)
3. Energy Harvesting
Substrate-level phosphorylation
! Nets two ATP molecules
2 ATP
used
4 ATP + 2 NADH
generated
Net
Gain/Glucose =
2 ATP + 2 NADH
! Universal: All living organisms
! Anaerobic process (no O2 required)
What do cells do with Pyruvate and NADH?
Depends on whether conditions are Aerobic or
Anaerobic
Under Aerobic (with O2)
Cellular Respiration
• Use Pyruvate and NADH to generate lots more ATP…
II. Stages of Aerobic Cellular Respiration
Overview
Cytoplasm
A. Glycolysis
Glucose
B. Pyruvate oxidation
C. Krebs (Citric Acid) Cycle
NADH
Glycolysis
ATP
D. Electron Transport Chain
Pyruvate
Pyruvate
oxidation
NADH
AcetylCoA
NADH
Krebs
cycle
Intermembrane
space
CO2
Mitochondrial matrix
CO2
ATP
FADH2
H2O
ATP
NAD+ and FAD
eMitochondrion
Electron
transport chain
Inner mitochondrial membrane
B. Pyruvate Oxidation
Mitochondrion
C. Kreb’s Cycles (Citric Acid Cycle)
II. Stages of Aerobic Cellular Respiration
Overview
Cytoplasm
A. Glycolysis
Glucose
B. Pyruvate oxidation
C. Krebs (Citric Acid) Cycle
NADH
Glycolysis
ATP
D. Electron Transport Chain
Pyruvate
Pyruvate
oxidation
NADH
Intermembrane
space
CO2
AcetylCoA
NADH
Krebs
cycle
Mitochondrial matrix
CO2
ATP
FADH2
H2O
ATP
NAD+ and FAD
e-
Electron
transport chain
Inner mitochondrial membrane
Mitochondrion
Electron Transport Chain: Generalized Scheme
1. NADH and FADH2 pass electrons to an electron transport chain
2. Energy is released as electrons “fall” and lose energy
3. Energy is harvested as ATP
NADH
ATP
+
NAD
+
2e
!
+
H
E
Tr lect
an ro
Ch spo n
ai rt
n
* Controlled release
of energy for ATP
synthesis!
+
2e
!
H
H2O
O2
H+
.
Protein
complex
H+
Intermembrane
space
Inner
mitochondrial
membrane
Mitochondrial
matrix
H+
H+
Electron
carrier
FADH2
NADH
H+
H+
H+
H+
ATP
H+ synthase
FAD
O 2 + H+
+
NAD
H
H+
H
+
H+
H
+
H2O
+
Electron Transport Chain
ADP + P
H+
ATP
ATP synthase
OXIDATIVE PHOSPHORYLATION =
One Type of Chemiosmosis
O2 is the final electron acceptor in the electron
transport chain; it is reduced to H20
ATP Synthase, Chemiosmosis & ATP Synthesis
CHEMIOSMOSIS:
The passage of high-energy
electrons along the electron
transport chain, which is
coupled to the pumping of
protons through ATP
synthase, driving the
production of ATP
ATP Synthase
II. Stages of Aerobic Cellular Respiration
Overview
Cytoplasm
A. Glycolysis
Glucose
B. Pyruvate oxidation
C. Krebs (Citric Acid) Cycle
NADH
Glycolysis
ATP
D. Electron Transport Chain
Pyruvate
Pyruvate
oxidation
NADH
Intermembrane
space
CO2
AcetylCoA
Mitochondrial matrix
NADH
CO2
Krebs
cycle
ATP
FADH2
H2O
ATP
NAD+ and FAD
e-
Electron
transport chain
Inner mitochondrial membrane
Mitochondrion
Aerobic Respiration Efficiency
Glucose
2 ATP
2 ATP
Glycolysis
Pyruvate
Acetyl-CoA
2 NADH
4 ATP
2 NADH
6 ATP
2 ATP
Krebs
cycle
6 NADH
18 ATP
2 FADH2
4 ATP
Total net ATP yield = 36
ATP
Contrasting Energy Yields
From 1 molecule of glucose:
• Aerobic respiration
–
–
–
–
–
Glycolysis (2 ATP)
Pyruvate Oxidation (none)
Citric Acid cycle (2 ATP)
Respiratory chain (32 ATP)
~ 36 total ATP
• Fermentation
– Glycolysis (2 ATP)
– Fermentation (none)
A. Fermentation Stage 1: Glycolysis
1
6-carbon glucose
(Starting material)
2 ATP
P
P
6-carbon sugar diphosphate
2
3
P
P
6-carbon sugar diphosphate
P
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
NADH
NADH
2 ATP
2 ATP
3-carbon
pyruvate
Priming reactions.
Cleavage reactions.
P
3-carbon
pyruvate
Energy-harvesting
reactions.
A. Fermentation Stage 2: Recycling NADH
Alcohol fermentation
Glucose
G
L
Y
C
O
L
Y
S
I
S
2 ADP
2 ATP
In cytoplasm
O–
C O
C O
CH3
Glucose
In cytoplasm
G
L
Y
C
O
L
Y
S
I
S
2 ADP
2 ATP
O–
C O
C O
CH3
2 NAD+
2 NADH
CO2
2 Pyruvate
Lactic acid fermentation
H
H C OH
CH3
2 Ethanol
H
C O
CH3
2 Acetaldehyde
O–
C O
H C OH
CH3
2 NAD+ 2 Lactate
Yeast cells (single
celled fungi)
Most animal cells,
lactate removed from
cells by blood
2 NADH
2 Pyruvate
B. Anaerobic respiration
! Archaebacteria Only
Methanogens
• Live in anaerobic environments (no oxygen)
• Use CO2 gas as final electron acceptor; convert to methane gas (CH4)
• Found in swamps, sewage treatment plants, digestive tracts of animals
• Break down cellulose for herbivores (cows)
• Produce marsh gas or intestinal gas (methane)
Sulfur Bacteria
• Live in anaerobic environments (no oxygen)
• Use inorganic sulfates (SO4) as final electron acceptor;
convert to hydrogen sulfide (H2S)
• Found in sulfur springs
Red Sulfur Bacteria
Summary: Respiration without oxygen
1. Glycolysis produces a net of 2ATP
2. Fermentation - recycles NADH to NAD+
»
»
»
Lactic acid fermentation
CO2 and Ethanol fermentation
NO Pyruvate Oxidation, NO Kreb’s Cycle, NO
electron transport!
3. Anaerobic Respiration
! Methanogens
Final electron acceptor: CO2,
convert to CH4
! Sulfate-reducing Bacteria
Final electron acceptor: SO4,
convert to to H2S
IV. Catabolism of Macromolecules
How is cellular E carried between coupled rxns?
Example: Using glucose E to build a protein