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Cellular
Respiration
Chapter 8
Cellular
Respiration
 There are two pathways for
cellular respiration.
 Anaerobic Pathway-glycolysis
and fermentation
 Aerobic pathway-glycolysis
paired with aerobic respiration in
the mitochondria.
 Carbohydrates produced in
photosynthesis are converted
into the energy of the cell, ATP.
Overall Equation:

C6H12O6 + 6O2
6CO2 + 6H2O + energy (ATP)
Respiration is a Redox
Reaction
•Oxidation-reduction
•LEO the lion says GER
•Oxidation is e- loss
•Reduction is e- gain
•Reducing agent is the edonor
•Oxidizing agent is the eacceptor
Oxidizing Agent
in Respiration
 NAD+
(nicotinamide adenine
dinucleotide)
 NAD + is reduced to
NADH
 Enzyme action:
dehydrogenase
 Oxygen is the
eventual e- acceptor
+
NAD
 Only a small amount of NAD+ is needed in cells; each
NAD+ is used over and over.
 Electrons received by NAD+ are high-energy
electrons and are usually carried to the electron
transport system.
 FAD coenzyme of oxidation-reduction can replace
NAD+.
 FAD accepts two electrons and becomes FADH2.
How Cells Acquire ATP
Glucose is high-energy
CO2 & H2O are low-energy
Process is exergonic and
releases energy.
Glucose is oxidized and
O2 is reduced.
Buildup of ATP is an endergonic rxn
that requires energy.
Breakdown of glucose yields
synthesis of 36 or 38 ATP,
preserving 39% of energy in glucose.
Cellular Respiration
 Glycolysis: occurs in cytosol;
degrades glucose into pyruvate
 Kreb’s Cycle: occurs in the
mitochondrial matrix; converts
pyruvate into carbon dioxide
 Electron Transport Chain:
inner membrane of
mitochondrion; electrons are
passed to oxygen
Order of Events
First we will look at
Glycolysis
and how it leads into
Aerobic Respiration.
*
* Second we will look at
our other pathway of
Glycolysis into
Fermentation.
Glycolysis
 Glycolysis is the breakdown of glucose to two pyruvate.
 Enough energy is released for immediate buildup of two
ATP.
 Two NADH are also produced.
 Glycolysis takes place outside the mitochondria and
does not utilize oxygen (anaerobic).
ATP Production in Glycolysis
Glycolysis
•Glucose (C6) splits into two
C3 molecules each with a
phosphate group.
 4 total ATP are produced but two are used to phosphorylate
glucose so there is a net gain of 2 ATP.
 The C3 molecules, pyruvate, enter the mitochondria if O2 is
available to continue with aerobic respiration.
 If no O2 is available, glycolysis becomes part of fermentation.
 Let’s look at an aerobic environment first…
Inside The Mitochondria
 Glucose breakdown
involves the transition
rxn, the Krebs cycle, and
the electron transport
system.
 A mitochondrion has a
double membrane with
an intermembrane space
between the outer and
inner membrane.
Inside the Mitochondria
Inside the Mitochondria
Outer Membrane
Intermembrane
space
Inner Membrane
Cristae
Matrix
•Jelly-like substance
•Transition Reaction and Kreb’s Cycle occur
here.
•Folds of inner
membrane.
•Increases surface
area for
chemiosmosis
•ETS occurs here
The Mitochondria
Transition Reaction
 The Transition Reaction links
Glycolysis and the Krebs cycle.
 Pyruvate is oxidized to an
acetyl group attached to coenzyme A and CO2 is removed.
 This happens
twice for each
glucose molecule.
The Krebs Cycle
 The Krebs cycle is a series of
reactions that give off CO2 and
producing ATP.
 It occurs in the matrix of the
mitochondria.
 The Krebs cycle produces two
immediate ATP molecules per
glucose molecule.
 6 NADH and 2 FADH2 are also
formed and carry electrons to the
ETS.
 CO2 is released- we exhale it.
The Electron Transport System
 Electron transport system is located in cristae of
mitochondria.
 Consists of carriers that pass electrons.
 Electrons pass from higher to lower energy states,
energy is released and stored for ATP production.
 Electrons that enter the electron transport system are
carried by NADH and FADH2
 NADH gives up electrons, becoming NAD+
 System accounts for 32 to 34 ATP depending on the
cell.
The Electron Transport System
 At each sequential oxidation-reduction rxn,
energy is released to form ATP.
 O2 serves as a terminal electron acceptor
and combines with hydrogen to form water.
 Because O2 must be present for system to
work, it is called oxidative phosphorylation.
The Electron Transport System
 At each sequential oxidation-reduction rxn,
energy is released to form ATP.
 O2 serves as a terminal electron acceptor
and combines with hydrogen to form water.
 Because O2 must be present for system to
work, it is called oxidative phosphorylation.
Cristae of
Mitochondria
 NADH dehydrogenase
complex, cytochrome b-c
complex, and cytochrome
oxidase complex all pump
H+ ions into the
intermembrane space.
Energy released from flow of electrons down
electron transport chain is used to pump H+ ions,
carried by NADH and FADH2, into intermembrane
space.
ATP Production in the
Mitochondria
 ATP synthase complexes are channel proteins that
also serve as enzymes for ATP synthesis.
 As H+ ions flow from high to low concentration,
ATP synthase synthesizes ATP (Chemiosmosis).
 Once formed, ATP molecules diffuse out of the
mitochondrial matrix through channel proteins.
Energy Yield From Glucose
Breakdown
Source
FADH2
Glycolysis
Glycolysis
Transition
Kreb’s
Kreb’s
Kreb’s
2 FADH2
TOTAL:
NADH
2 NADH
2 NADH
6 NADH
ATP
2 ATP
4-6 ATP
6 ATP
2 ATP
18 ATP
4 ATP
36-38
ATP
Anaerobic Pathway
 If O2 is not available to the cell,
fermentation, an anaerobic process, occurs.
 During fermentation, glucose is
incompletely metabolized to lactate or CO2
and alcohol.
 Fermentation results in a net gain of only 2
ATP per glucose molecule.
Fermentation
 Fermentation consists of
glycolysis plus reduction
of pyruvate to either
lactate or alcohol and
CO2.
 NADH passes its
electrons to pyruvate
instead of to an electron
transport system.
 NAD+ is then free to
return and pick up more
electrons during earlier
rxns of glycolysis.
Fermentation
Examples
Yeasts use CO2 to make
bread rise and produce ethyl
alcohol in wine-making.
Animals produce pyruvate
to lactate when it is produced
faster than it can be oxidized
by Krebs cycle.
 Anaerobic bacteria produce
lactic acid when we
manufacture some cheeses.
 Anaerobic bacteria produce
industrial chemicals:
isopropanol, butyric acid, etc.
Advantages and Disadvantages
of Fermentation
 Fermentation provides quick bursts of ATP
energy for muscular activity.
 Disadvantage is that lactate is toxic to cells.
 When blood can’t remove lactate from
muscles, lactate changes pH and causes
muscles to fatigue.
 Individual is in oxygen debt b/c oxygen is
still needed after exercising.
 Recovery occurs after lactate goes to liver.
Efficiency of Fermentation
 Two ATP produced per glucose
molecule during fermentation .
 Fermentation is much less efficient
than complete breakdown of glucose
in oxidative phosphorylation..