Organisms generate energy through cellular respiration, which has three main stages. In glycolysis, glucose is broken down to pyruvate, producing a small amount of ATP. Pyruvate then enters the citric acid cycle in the mitochondrion, producing more ATP, NADH, and FADH2. These electron carriers supply the electron transport chain, where electrons are transferred to oxygen in a series of redox reactions. This pumps protons out of the mitochondrion, building up a proton gradient that ATP synthase uses to produce the majority of ATP through oxidative phosphorylation.

2.  Organisms must take in
energy from outside
sources.
 Energy is incorporated
into organic molecules
such as glucose in the
process of
photosynthesis.
 Glucose is then broken
down in cellular
respiration. The energy
is stored in ATP.

3. Fig. 9-2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O
Cellular respiration
in mitochondria
Organic
molecules
+ O2
ATP powers most cellular work
Heat
energy
ATP
The
Flow of
Energy
from
Sunlight
to ATP

4.  Energy in food is stored as carbohydrates
(such as glucose), proteins & fats. Before
that energy can be used by cells, it must be
released and transferred to ATP.

5.  Aerobic Cellular Respiration: the process that
releases energy by breaking down food
(glucose) molecules in the presence of oxygen.
 Formula: C6H12O6 + 6O2 → 6CO2 + 6H2O +~ 36 ATP
 Fermentation: the partial breakdown of glucose
without oxygen. It only releases a small amount
of ATP.
 Glycolysis: the first step of breaking down
glucose—it splits glucose (6C) into 2 pyruvic
acid molecules (3C each)

6.  The transfer of electrons during chemical
reactions releases energy stored in organic
compounds such as glucose.
 Oxidation-reduction reactions are those that
involve the transfer of an electron from one
substance to another.

7.  Chemical reactions that transfer electrons between
reactants are called oxidation-reduction reactions,
or redox reactions
• In oxidation, one substance loses electrons, or is
oxidized
 In reduction, a substance gains electrons, or is
reduced (the amount of positive charge is reduced)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Na will easily lose its outer
electron to Cl . Why?
In this reaction, which atom is
oxidized?
Which is reduced?

8. becomes oxidized
becomes reduced
In cellular respiration, glucose is broken down and
loses its electrons in the process.
The glucose becomes oxidized and the Oxygen is
reduced.
Redox Reactions of Cellular Respiration

9.  In cellular respiration, glucose is broken down
in a series of steps.
 As it is broken down, electrons from glucose
are transferred to NAD+, a coenzyme
 When it receives the electrons, it is converted to
NADH.
NADH
represents
stored energy
that can be
used to make
ATP

10.  NADH passes the electrons to the electron
transport chain, a series of proteins embedded
in the inner membrane of the mitochondria.
 The electrons (and the energy they carry) are
transferred from one protein to the next in a
series of steps.

11. Freeenergy,G
Freeenergy,G
(a) Uncontrolled reaction
H2O
H2 + 1
/2 O2
Explosive
release of
heat and light
energy
(b) Cellular respiration
Controlled
release of
energy for
synthesis of
ATP
2 H+
+ 2 e–
2 H + 1
/2 O2
(from food via NADH)
ATP
ATP
ATP
1
/2 O2
2 H+
2 e–
Electrontransport
chain
H2O
Energy is released a little at a time, rather than one big explosive reaction:

12.  Cellular respiration has three stages:
 Glycolysis (breaks down glucose into two molecules of
pyruvate)
 The Citric Acid cycle/Kreb’s Cycle (completes the
breakdown of glucose)
 Electron Transport Chain and Oxidative
phosphorylation (accounts for most of the ATP
synthesis)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

13. Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH
An Overview of Cellular Respiration–Part 1

14. Mitochondrion
Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH
Substrate-level
phosphorylation
ATP
Electrons carried
via NADH and
FADH2
Citric
acid
cycle
An Overview of Cellular Respiration—Part 2

15. Mitochondrion
Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH
Substrate-level
phosphorylation
ATP
Electrons carried
via NADH and
FADH2
Oxidative
phosphorylation
ATP
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
An Overview of Cellular Respiration—Part 3

20.  Substrate-level
phosphorylation:
 Phosphate is added to
ADP to make ATP by
using an enzyme:
 Oxidative
phosphorylation:
 Phosphate is added to
ADP to make ATP by
ATP Synthase—a
protein embedded in
the mitochondria
membrane (requires
O2)
WAY MORE
EFFICIENT!!
PRODUCES LOTS
MORE ATP!

21.  “Glyco”=sugar; “lysis”=to split
 In this first series of reactions, glucose (C6) is
split into two molecules of pyruvic acid (C3).
 This occurs in the cytoplasm of cells and does
not require oxygen.
 This releases only 2 ATP molecules, not
enough for most living organisms.

22. Energy investment phase
Glucose
2 ADP + 2 P 2 ATP used
formed4 ATP
Energy payoff phase
4 ADP + 4 P
2 NAD+
+ 4 e–
+ 4 H+
2 NADH + 2 H+
2 Pyruvate + 2 H2O
2 Pyruvate + 2 H2OGlucose
Net
4 ATP formed – 2 ATP used 2 ATP
2 NAD+
+ 4 e–
+ 4 H+
2 NADH + 2 H+
Glycolysis

23.  The Citric Acid Cycle (also called the Kreb’s
Cycle) completes the breakdown of pyruvate
and the release of energy from glucose.
 It occurs in the matrix of the mitochondria.

24.  In the presence of oxygen, pyruvate enters the
mitochondria.
 Before the pyruvate can enter the Citric Acid
Cycle, however, it must be converted to Acetyl
Co-A.
 Some energy is released and NADH is formed.

25. CYTOSOL MITOCHONDRION
NAD+
NADH + H+
2
1 3
Pyruvate
Transport protein
CO2
Coenzyme A
Acetyl CoA
Converting Pyruvate to Acetyl CoA:

26.  The Acetyl Co-A enters the Citric Acid Cycle in
the matrix of the mitochondria.
 The Citric Acid cycle breaks down the Acetyl
Co-A in a series of steps, releasing CO2
 It produces 1 ATP, 3 NADH, and 1 FADH2 per
turn.

27. • The Citric Acid cycle (also called the Krebs Cycle)
has eight steps, each catalyzed by a specific
enzyme
• The acetyl group of acetyl CoA joins the cycle by
combining with oxaloacetate, forming citrate
(Citric Acid).
• The next seven steps decompose the citrate
(Citric Acid) back to oxaloacetate, making the
process a cycle
The Citric Acid Cycle
Oxaloacetate + Acetyl CoA Citric Acid

28. Acetyl CoA
CoA—SH
Citrate
H2O
Isocitrate
NAD+
NADH
+ H+
CO2
α-Keto-
glutarate
CoA—SH
CO2
NAD+
NADH
+ H+
Succinyl
CoA
CoA—SH
Pi
GTP GDP
ADP
ATP
Succinate
FAD
FADH2
Fumarate
Citric
acid
cycleH2O
Malate
Oxaloacetate
NADH
+H+
NAD+
1
2
3
4
5
6
7
8
The
Citric
Acid
Cycle:

29. • Each Citric Acid Cycle only produces 1 ATP
molecule. The rest of the energy from pyruvate
is in the NADH and FADH2.
• The NADH and FADH2 produced by the Citric
Acid cycle relay electrons extracted from food
to the electron transport chain.

30.  The electron transport chain is in the cristae of
the mitochondrion
 Most of the chain’s components are proteins,
which exist in multiprotein complexes
 The carriers alternate reduced and oxidized
states as they accept and donate electrons
 Electrons drop in free energy as they go down
the chain and are finally passed to O2, forming
H2O
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Oxygen is the final electron acceptor.

31. NADH
NAD+
2
FADH2
2 FAD
Multiprotein
complexesFAD
Fe•S
FMN
Fe•S
Q
Fe•S
Ι
Cyt b
Ι
Ι
ΙΙ
Ι
Cyt c1
Cyt c
Cyt a
Cyt a3
IV
Freeenergy(G)relativetoO2(kcal/mol)
50
40
30
20
10 2
(from NADH
or FADH2)
0 2 H+
+ 1
/2
O2
H2O
e–
e–
e–
The
Electron
Transport
Chain

32.  Electrons are transferred from NADH or
FADH2 to the electron transport chain
 Electrons are passed through a number of
proteins to O2
 The chain’s function is to break the large free-
energy drop from food to O2 into smaller steps
that release energy in manageable amounts

33.  Electron transfer in the electron transport chain
causes proteins to pump H+
from the
mitochondrial matrix to the intermembrane
space
 H+
then moves back across the membrane,
passing through channels in ATP synthase

34.  ATP synthase uses the exergonic flow of H+
to
drive phosphorylation of ATP
 This is an example of chemiosmosis, the use of
energy in a H+
gradient to drive cellular work

35. INTERMEMBRANE SPACE
Rotor
H+
Stator
Internal
rod
Cata-
lytic
knob
ADP
+
P ATP
i
MITOCHONDRIAL MATRIX
ATP
Synthase

36. Protein
complex
of electron
carriers
H+
H+
H+
Cyt c
Q
Ι
ΙΙ
ΙΙ
Ι
ΙV
FADH2
FAD
NAD+
NADH
(carrying electrons
from food)
Electron transport chain
2 H+
+ 1
/2O2 H2O
ADP + P
i
Chemiosmosis
Oxidative phosphorylation
H+
H+
ATP
synthase
ATP
21
Chemiosmosis couples the electron transport chain to ATP
synthesis

37.  During cellular respiration, most energy flows
in this sequence:
glucose → NADH → electron transport chain
→ proton-motive force → ATP
 About 40% of the energy in a glucose molecule
is transferred to ATP during cellular
respiration, making about 38 ATP
+ 6 O2 6CO2 + 6H2O + 38 ATP

38. Maximum per glucose: About
36 or 38 ATP
+ 2 ATP+ 2 ATP + about 32 or 34 ATP
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Citric
acid
cycle
2
Acetyl
CoA
Glycolysis
Glucose
2
Pyruvate
2 NADH 2 NADH 6 NADH 2 FADH2
2 FADH2
2 NADH
CYTOSOL Electron shuttles
span membrane
or
MITOCHONDRION
ATP Yield per molecule of glucose at each stage of cellular
respiration: