Chapter 9 Cellular respiration: Harvesting Chemical energy

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Chapter 9Cellular respiration Harvesting
Chemical energy

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Figure 9.1 Energy flow and chemical recycling in
ecosystems
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REDOX (Reduction/Oxidation)

• Redox can involve loss or gain of an electron or
  a hydrogen (contains an electron)
• C6H12O6 6O2 ---gt 6CO2 6H2O
• Carbon loses hydrogen therefore is oxidized.
• Oxygen gains hydrogen therefore is reduced.

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Figure 9.3 Methane combustion as an
energy-yielding redox reaction
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Figure 9.4 Nicotinamide Adenine Dinucleotide as
an electron shuttle

• 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 gt NADH H

FAD 2H FADH2
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Figure 6.8 The structure and hydrolysis of ATP
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Figure 6.10 The ATP cycle
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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

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2 ways to make ATP

• Substrate level phosphorylation
• Transfer of a phosphate from an organic molecule
  to ADP to form ATP
• Phosphoenolpyruvate (PEP)
• Aerobic respiration/electron transport system
• Use of NADH H (reduced form) to provide energy
  to make ATP
• Requires presence of oxygen (O2)

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Mitochondria
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Figure 9.6 An overview of cellular respiration
(Layer 3)
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Glucose
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5
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4

• 2

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C6H12O6 6O2 ---gt 6CO2 6H2O
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Figure 9.9 A closer look at glycolysis energy
investment phase (Layer 2)
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Figure 9.9 A closer look at glycolysis energy
payoff phase (Layer 4)
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Figure 9.8 The energy input and output of
glycolysis

• Metabolic Energy Production Summary
• C6H12O6 6O2 6H2O 6CO2 energy (36 ATP)
• 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)

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Figure 9.6 An overview of cellular respiration
(Layer 3)
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Figure 9.18 Pyruvate as a key juncture in
catabolism
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Figure 9.17a Fermentation
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Figure 9.17b Fermentation
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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
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Figure 9.11 A summary of the Krebs cycle
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Figure 9.11 A closer look at the Krebs cycle
(Layer 4)
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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)
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Figure 9.6 An overview of cellular respiration
(Layer 3)
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Figure 9.5 An introduction to electron transport
chains
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Mitochondria
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Figure 9.14 ATP synthase, a molecular mill
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Figure 9.13 Free-energy change during electron
transport

• FMN Flavin Mononucleotide
• FeS Iron Sulfur protein
• Q Ubiquinone
• Cyt Cytochromes

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Figure 9.15 Chemiosmosis couples the electron
transport chain to ATP synthesis
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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)
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Figure 9.16 Review how each molecule of glucose
yields many ATP molecules during cellular
respiration
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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
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Figure 9.20 The control of cellular respiration 
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Figure 9.19 The catabolism of various food
molecules
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b-oxidation

• Invest ATP to prime system (-1ATP)
• Harvest FADH2 (2ATP)
• Harvest NADH (3ATP)
• Net gain 4ATP
• Plus 12 ATP from Krebs cycle