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NOTES: Ch 9
Cellular
Respiration:
Harvesting
Chemical Energy
Part 1: The
Overview
Overview: Life Is Work
● Living cells require energy from outside
sources
● Some animals, such as the giant panda,
obtain energy by eating plants; others
feed on organisms that eat plants
● Energy flows into an ecosystem as
sunlight and leaves as heat
● Photosynthesis generates oxygen and
organic molecules, which are used in
cellular respiration
● Cells use chemical energy stored in
organic molecules to regenerate ATP,
which powers work
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic + O
molecules 2
CO2 + H2O
Cellular respiration
in mitochondria
ATP
powers most cellular work
Heat
energy
9.1 - Catabolic Pathways & Production
of ATP:
● The breakdown of organic molecules is
EXERGONIC
● Fermentation is a partial degradation of
sugars that occurs without oxygen
● Cellular respiration consumes oxygen
and organic molecules and yields ATP
Principles of Energy Harvest
● Although carbohydrates, fats, and proteins are all
consumed as fuel, it is helpful to trace cellular
respiration with the sugar glucose:
Chemical Equation:
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
(ATP + heat)
Recall: the ATP cycle
Redox Reactions: Oxidation and
Reduction
● The transfer of electrons during chemical
reactions releases energy stored in
organic molecules
● This released energy is ultimately used to
synthesize ATP
● REDOX REACTIONS: involve electron
transfers from 1 substance to another
The Principle of Redox
● OXIDATION: loss of electrons
(“energy releasing”)
● REDUCTION: gain of electrons
(“energy storing”)
Example of Redox:
Oxidation
(loss of electrons)
Na
+
Cl 
Na+
Reduction
(gain of electrons)
+
Cl-
● The electron donor is called the reducing
agent
● The electron receptor is called the
oxidizing agent
Example of Redox:
Na is oxidized;
it is the reducing agent
Na
+
Cl 
Na+
+
Cl is reduced;
it is the oxidizing agent
Cl-
Oxidation of Organic Fuel Molecules
During Cellular Respiration:
● During cellular respiration, the fuel
(such as glucose) is oxidized and
oxygen is reduced:
Respiration:
oxidized
C6H12O6 + 6O2 
6CO2 + 6H2O
reduced
*the transfer of electrons from 1 element
to another, more electronegative
element (e.g. from H to O) releases
stored potential energy - - this chemical
energy can be put to work!
● Glucose & other fuels are broken down
gradually, in a series of steps
● at key steps, H atoms are stripped from
glucose and passed to a coenzyme: NAD+
– (this is performed by enzymes:
dehydrogenase)
NAD+ + 2H  NADH + H+
Stepwise Energy Harvest via NAD+ and the
Electron Transport Chain
● As an electron acceptor, NAD+ functions
as an oxidizing agent during cellular
respiration
● Each NADH (the reduced form of NAD+)
represents stored energy that is tapped
to synthesize ATP
2 e– + 2 H+
NAD+
2 e– + H+
H+
NADH
Dehydrogenase
+ 2[H]
(from food)
Nicotinamide
(oxidized form)
+
Nicotinamide
(reduced form)
H+
● Respiration uses an ELECTRON
TRANSPORT CHAIN to break the fall
of electrons into several energyreleasing steps (instead of one
explosive reaction)
e-
● NADH passes the electrons to the electron
transport chain
● Oxygen pulls electrons down the chain in an
energy-yielding tumble
● The energy yielded is used to regenerate ATP
H2 + 1/2 O2
+
2H
1 /2
O2
1/2
O2
(from food via NADH)
Explosive
release of
heat and light
energy
Free energy, G
Free energy, G
2 H+ + 2 e–
Controlled
release of
energy for
synthesis of
ATP
ATP
ATP
ATP
2 e–
2
H+
H2O
Uncontrolled reaction
H2O
Cellular respiration
ELECTRON TRANSPORT CHAIN:
● consists of molecules, mostly proteins,
built into the inner membrane of
mitochondria
● NADH carries the electrons to the
“top” of the chain
● oxygen captures electrons at the
“bottom” of the chain and combines with
H+, forming water.
Reduction of
oxygen!
SUMMARY OF ENERGY
FLOW IN THE CELL:
Food  NADH  E.T.C.  oxygen
(glucose)
**oxygen is the final electron acceptor!
The Stages of Cellular Respiration:
A Preview
● Cellular respiration has three stages:
1) Glycolysis (breaks down glucose into two
molecules of pyruvate)
2) The Citric Acid Cycle, a.k.a. Krebs Cycle
(completes the breakdown of glucose)
3) E.T.C. & Oxidative phosphorylation
(accounts for most of the ATP synthesis)
Glycolysis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Substrate-level
phosphorylation
Glycolysis
Pyruvate
Glucose
Cytosol
Citric
acid
cycle
Mitochondrion
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Cytosol
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
ATP Synthesis:
● The process that generates most of the ATP is
called oxidative phosphorylation because it
is powered by redox reactions
● Oxidative phosphorylation accounts for almost
90% of the ATP generated by cellular
respiration
ATP Synthesis:
● A small amount of
ATP is formed in
glycolysis and the
citric acid cycle by
substrate-level
phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
+
Product
ATP