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Chapter 9
Cellular respiration: Harvesting Chemical energy
Figure 9.1 Energy flow and chemical recycling in ecosystems
Figure 9.3 Methane combustion as an energy-yielding redox reaction
Figure 9.4 Nicotinamide Adenine Dinucleotide + as an electron shuttle
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•
•
•
NAD+ is reduced to form NADH by gaining a hydrogen atom..and
an electron to balance the charge
The electron come from water therefore a proton is formed
Therefore…
NAD+ > NADH + H+
FAD +2H
FADH2
Figure 6.8 The structure and hydrolysis of ATP
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Cell and Organismal Biology 2009
Figure 6.10 The ATP cycle
Cell and Organismal Biology 2009
8.11 A review of how ATP drives cellular work
Roles for ATP
ATP
also provides phosphates and energy to phosphorylate
and therefore activate or deactivate proteins
2 ways to make ATP
•
Substrate level phosphorylation
–
–
•
Transfer of a phosphate from an organic molecule to ADP to
form ATP
Phosphoenolpyruvate (PEP)
Oxidative phosphorylation/electron transport system
–
Use of NADH + H+ (reduced form) to provide energy to make
ATP
–
Requires presence of oxygen (O2)
Mitochondria
Figure 9.6 An overview of cellular respiration (Layer 3)
Glucose
6
5
1
4
3
2
C6H12O6 + 6O2 ---> 6CO2 + 6H2O
Figure 9.9 A closer look at glycolysis: energy investment phase (Layer 2)
Figure 9.9 A closer look at glycolysis: energy payoff phase (Layer 4)
Figure 9.8 The energy input and output of glycolysis
Metabolic Energy Production Summary
C6H12O6 + 6O2
(36 ATP)
6H2O + 6CO2 + energy
1. Glycolysis: (Outside mitochondria in the
cytoplasm)
•Glucose (6-carbon) is phosphorylated to
Fructose 1,6-bisphosphate (2 ATP used up)
•F 1,6 BP split to two PGAL(G3P)(3-carbon
each)
•Two PGAL phosphorylated to two DPGA
(BPG)(2 NADH +2H+ produced)
•Two DPGA dephosphorylated to two
pyruvate molecules (3-carbon) (4 ATP
produced)
Net Gain: 2 NADH + H+; 2ATP. (These two
ATPs may be used up transporting the
NADH + H+ to the mitochondria)
Figure 9.6 An overview of cellular respiration (Layer 3)
Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the
Krebs cycle (Citric Acid Cycle)
2. Preparation for Krebs cycle: (In mitochondria)
CO2 removed from pyruvate as Acetyl-CoA formed (2 NADH + 2H+
produced per 2 pyruvate)
Net Gain: 2 NADH + H+
Figure 9.11 A summary of the Krebs cycle
Figure 9.11 A closer look at the Krebs cycle (Layer 4)
3. Citric Acid Cycle (Krebs Cycle, CAC) (In mitochondria)
Acetyl-CoA combines with oxaloacetic acid (4-carbon) to give 6-carbon molecule.
Molecule gradually rearranged and broken down. Co-A is re-used. Oxaloacetic acid
regenerated for re-use.
2 x 3 NADH + H+ produced (2 x 3 because two Acetyl-CoA enter cycle per glucose)
2 x 1 FADH2 produced
2 x 1GTP produced (later converted to ATP)
2 x 2 CO2 released
So, glucose completely broken down to CO2 and high energy compounds
produced
Net Gain
10 NADH + H+
2 FADH2
2 ATP (via GTP) (This is used directly in the cell)
Figure 9.6 An overview of cellular respiration (Layer 3)
Figure 9.5 An introduction to electron transport chains
Mitochondria
Figure 9.14 ATP synthase, a molecular mill
Figure 9.13 Free-energy change during electron transport
• FMN
• FeS
• Q
• Cyt
Flavin
Mononucleotide
Iron Sulfur
protein
Ubiquinone
Cytochromes
Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis
4. Chemiosmotic ATP Synthesis: (In inner mitochondrial membrane)
NADH + H+ releases electrons (2e-) plus hydrogen ions (2H+) to electron
transport chain. NAD+ goes back to earlier stages and is reused. Electrons
pass across the membrane three times, carrying 2H+ across each time, and
leaving them between the inner and outer mitochondrial membranes. So each
NADH +H+ carries six hydrogen ions across. Electrons from FADH2 carry four
hydrogen ions across. FAD is also re-used in CAC.
So, for each glucose molecule, 68 hydrogen ions are moved across the inner
mitochondrial membrane.
It takes 2 hydrogen ions moving through the ATP
synthase enzyme to convert ADP + Pi to ATP (34 total.)
The electron pairs must now combine with half of an O2 molecule, and two H+
to give H2O. This is the source of the water in the respiration equation.
Net Gain
10 NADH + H+
2 FADH2
2 ATP (via GTP) (This is used directly in the cell)
Figure 9.16 Review: how each molecule of glucose yields many ATP molecules during
cellular respiration
5.
Conclusion
So, 34 ATP are formed by chemisosmotic ATP synthesis. Add these to the net
gain of 2 ATP from the Krebs Cycle to give a grand total of 36 ATPs formed from
one molecule of glucose as it is broken down to six CO2 and 6H2O molecules.
The ATP is then used elsewhere in the cell.
Depending on how the cytosolic electrons are transferred to the mitochondria,
yield may include the ATPs from Glycolysis (so, yield may be 38 ATP)
Note that this is the theoretical yield.
Actual yield is lower
Figure 9.18 Pyruvate as a key juncture in catabolism
Figure 9.17a Fermentation
Figure 9.17b Fermentation
Figure 9.20 The control of cellular respiration
Figure 9.19 The catabolism of various food molecules
Cell and Organismal Biology 2009
-oxidation
• Invest ATP to prime
system (-1ATP)
• Harvest FADH2 (2ATP)
• Harvest NADH (3ATP)
• Net gain 4ATP
• Plus 12 ATP from Krebs
cycle