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Chapter 6
ACQUIRING ENERGY
Energy for Life
• All energy comes from the sun
– Producers convert light into chemical
energy (glucose bonds)
– Consumers eat/break bonds to release
energy
• Energy coupling reactions recycle
components
– Cellular respiration (break):
• 6O2 + C6H12O6  6CO2 + 6H2O + ATP
– Photosynthesis (make):
• ATP + 6CO2 + 6H2O  C6H12O6 + 6O2
• Which reaction term applies to each?
Redox Reactions
• Coupled reactions that move electrons between
molecules
– Review: electrons form bonds and energy is released
when they break (endergonic or exergonic?)
• LEO goes GER
– Lose an electron = oxidation
• Glucose oxidized to CO2
– Gain an electron = reduction
• O2 reduced to H20
• NAD+ reduced to NADH
– What do all these reactions have in common?
Electron Carriers
• NADH and NADPH hold e-’s = high energy bonds
– Carry 2 e-’s and a H+
– Precursor = NAD + and NADP +
• Molecules oxidized  e-’s released & captured
– Dehydrogenase
Cellular Respiration
• Aerobic respiration
– Requires O2
– High energy (ATP) yield
– Glycolysis
• Common to all paths
• Energy from sugar (glucose)
– Citric acid cycle (Kreb’s cycle)
• Requires O2
– Oxidative phosphorylation
(ETS and Chemiosmosis)
• Requires O2
• Anaerobic respiration
– Doesn’t require O2
– Organisms w/o mitochondria
– Low energy yield
Step 1: Glycolysis
• Aerobic and anaerobic
• In the cytoplasm
• Starts with:
– Glucose (6C’s)
– 2 ATP
• Ends with:
– 2 pyruvate (3C’s)
• Important products of this
process:
– Net 2 ATP
• 4 ATP  substrate-level
phosphorylation
– 2 NADH
Intermediate Step: ‘Grooming’
• Starts with:
– 2 Pyruvate (3C’s)
• High energy product
• Ends with:
– 2 Acetyl-CoA (2C’s)
• Important products of this process:
– 2 CO2
• Decarboxylation
– 2 NADH
Step 2: Citric Acid Cycle
• In the mitochondrial matrix
• Starts with:
– 2 Acetyl CoA
• Ends with:
– 4 CO2
• Important products of this
process:
– 2 ATP  substrate level
phosphorylation
– 6 NADH
– 2 FADH2
6 C’s
4 C’s
4 C’s
Step 3: Electron Transport System (ETS)
• In the inner mitochondrial membrane
• Starts with:
– 10 NADH (previous steps)
– 2 FADH2 (citric acid cycle)
– O2
• Ends with:
– H2O
• Important products of
this process:
– H + gradient
Electrons and the Importance of Oxygen
• Review
– Electron energy determined by arrangement
• e-’s further from the nucleus = more PE
• e-’s dropping levels release E
– Oxygen is highly electronegative
• Integral protein complexes use a little less energy to ‘hold’ the
electrons
• Extra energy transports a H+ across out of the matrix into the
intermembrane space
• O2 is the last molecule to accept e-’s to become water
Electrons from reactions in
glycolysis and Kreb’s cycle
Step 4: ATP Generation (Chemiosmosis)
• In the inner mitochondrial membrane
• Starts with:
– H + gradient
• Ends with:
– 32 – 34 ATP
• ATP synthase facilitates
A Review of Cellular Respiration
Substrate level
phosphorylation
Fermentation
• If no O2 available
• Starts with:
– Glucose
• Ends with:
– Lactate or
– CO2 and ethanol
• Important products of this process:
– 2 pyruvate
– 2 ATP
– 2 NADH/NAD+
• Makes yogurt, bread, alcoholic
beverages