1. Chapter 7 practice quiz
1. Describe the fluid-mosaic model of membranes.
2. Which of the following is not a function of membrane proteins?
Signal transduction, intercellular joining, protein packaging, enzymatic activity
3. _______ are used in cell-cell recognition.
4. _______transport requires energy while ______ transport does not.
5. True or False: The sodium potassium pump and proton pump are both
examples of passive transport.
6. During _____ water molecules move from less concentrated solute to more
concentrated solute.
7. Describe the difference between a hypotonic, isotonic and hypertonic
solution. What is the net water movement in each condition?
8. ______ proteins act as tunnels for which certain molecules can pass while
_____ proteins undergo changes in shape to facilitate transport across a
membrane.
9. What are the three mechanisms used for bulk transport?

2. Chapter 9
Cellular Respiration:
Harvesting Chemical Energy
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. Fig. 9-2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O Organic
+O
molecules 2
Cellular respiration
in mitochondria
ATP
ATP powers most cellular work
Heat
energy

4. Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is exergonic
• Fermentation is a partial degradation of sugars that occurs
without O2
• Anaerobic respiration harvests chemical energy without
using O2
• Aerobic respiration (aka cellular respiration) consumes
organic molecules and O2 and yields ATP
– Organic compounds + O2  CO2 + H20 + Energy
– C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5. Redox Reactions: Oxidation and Reduction
• Chemical reactions that transfer electrons between
reactants are called oxidation-reduction reactions, or redox
reactions
• In oxidation, a substance loses electrons, or is oxidized
• In reduction, a substance gains electrons, or is reduced
(the amount of positive charge is reduced)
• Redox reactions will always be between a fuel and oxygen
– This reaction is exergonic because it moves electrons towards the
more electronegative atom (oxygen)
– This released energy is ultimately used to synthesize ATP

6. Redox Rxn: Electron transfer from X to Y
becomes oxidized
becomes reduced
Electron Electron
donor = acceptor =
reducing oxidizing
agent agent
Xe- reduces Y by adding an electron to it.
Y oxidizes Xe- by removing an electron from it.
Fig. 9-UN2

7. Redox Rxn: cellular respiration
becomes oxidized
becomes reduced
Fuel is oxidized and the oxygen is reduced.
Oxidation of glucose transfers electrons to a lower energy state,
releasing energy which can be used to regenerate ATP
Organic molecules with lots of H are good fuels because for
each electron (from H) donated to oxygen, energy is released
Fig. 9-UN3

8. Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain
• In cellular respiration, glucose and other organic molecules
are broken down in a series of steps
• Electrons from organic compounds are usually first
transferred to NAD+ (nicotinamide adenine dinucleotide), a
coenzyme
• As an electron acceptor or carrier, 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
• NAD+ is reduced to NADH
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9. During cellular respiration…
• NADH passes the electrons to the electron transport
chain (exergonic process)
• The electron transport chain passes electrons in a series
of steps instead of one explosive reaction
– O2 pulls electrons down the chain in an energy-yielding
tumble
• Electrons removed from glucose are shuttled by NADH
to the higher-energy end of the chain
• O2 captures these electrons at the lower-energy end with
H protons to form water
• The energy yielded is used to regenerate ATP
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

10. During cellular respiration
• During cellular respiration, most electrons
travel the following “downhill” route:
Glucose  NADH  ETC  oxygen
• Energy is released as the electron reaches
oxygen
• Cellular respiration is exergonic

11. Fig. 9-5
(a) Uncontrolled reaction (b) Cellular respiration
H2 + 1/2 O2 2H + 1
/2 O2
(from food via NADH)
Controlled
release of
2 H+ + 2 e– energy for
synthesis of
ATP
Elec
ATP
Free energy, G
Free energy, G
tron ain
Explosive ATP
release of
ch
tran
heat and light ATP
energy
spor
2 e–
t
1
/2 O2
2H +
H2O H2O
Moving electrons closer to an electronegative element releases energy

12. The Stages of Cellular Respiration: A Preview
• Cellular respiration has three stages:
– Glycolysis (breaks down glucose into two
molecules of pyruvate)
– The citric acid cycle (completes the
breakdown of glucose)
– Oxidative phosphorylation (accounts for
most of the ATP synthesis)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

13. Fig. 9-6-1
Electrons
carried
via NADH
Glycolysis
Glucose Pyruvate
Cytosol
ATP
Substrate-level
phosphorylation

14. Fig. 9-6-2
Electrons Electrons carried
carried via NADH and
via NADH FADH2
Citric
Glycolysis acid
Glucose Pyruvate
cycle
Mitochondrion
Cytosol
ATP ATP
Substrate-level Substrate-level
phosphorylation phosphorylation

15. Fig. 9-6-3
Electrons Electrons carried
carried via NADH and
via NADH FADH2
Citric Oxidative
Glycolysis acid
phosphorylation:
electron transport
Glucose Pyruvate
cycle and
chemiosmosis
Mitochondrion
Cytosol
ATP ATP ATP
Substrate-level Substrate-level Oxidative
phosphorylation phosphorylation phosphorylation

16. Production of ATP during cellular respiration
• Oxidative phosphorylation generates most of the ATP
because it is powered by redox reactions
– accounts for almost 90% of the ATP generated by cellular
respiration
• A smaller amount of ATP is formed in glycolysis and the
citric acid cycle by substrate-level phosphorylation
Enzyme Enzyme
ADP
P
+ ATP
Substrate
Product
Phosphate is taken from a substrate to convert ADP to ATP

17. Glycolysis harvests chemical energy by oxidizing
glucose to pyruvate
• Glycolysis (“splitting of sugar”) breaks down
glucose into two molecules of pyruvate
• Glycolysis occurs in the cytoplasm and has two
major phases:
– Energy investment phase (cell spends ATP)
– Energy payoff phase (cell produces energy)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

18. Fig. 9-8
Energy investment phase
Glucose
2 ADP + 2 P 2 ATP used
Energy payoff phase
Via substrate-level
4 ADP + 4 P 4 ATP formed
phosphorylation
2 NAD+ + 4 e– + 4 H+ NAD+ is reduced to
2 NADH + 2 H+
NADH by electrons
released from the
oxidation of glucose
2 Pyruvate + 2 H2O
Net
Glucose 2 Pyruvate + 2 H2O
No CO2 is released
4 ATP formed – 2 ATP used 2 ATP during glycolysis
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

19. Glycolysis practice quiz
1. What are the three stages of cellular respiration?
2. Why is cellular respiration an exergonic process?
3. reducing
An electron donor is called the _____________ agent while the electron
4. oxidizing
acceptor is the ____________ agent.
5. True or False: CO2 is a biproduct of glycolysis.
6. Chart the path an electron takes during cellular respiration.
7. What is the benefit of the electron transport chain in cellular respiration.
8. Describe two ways in which ATP is produced during cellular respiration.
9. What is the net energy output as a result of glycolysis?

20. The citric acid cycle completes the energy-yielding
oxidation of organic molecules
• In the presence of O2, pyruvate enters the mitochondrion
where the oxidation of glucose is completed
• Before the citric acid cycle can begin, pyruvate must be
converted to acetyl CoA, which links the cycle to glycolysis
1. Removal of CO2 from pyruvate
2. NAD+ is reduced to NADH
3. Coenzyme A (CoA) is attached by an unstable bond
• Acetyl CoA can now be fed into CAC
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

21. Fig. 9-10
Conversion of pyruvate to acetyl CoA
CYTOSOL MITOCHONDRION
NAD+ NADH + H+
2
1 3
Acetyl CoA
Pyruvate CO2 Coenzyme A
Unstable bond in acetyl CoA makes entering the CAC an exergonic process

22. During the Citric Acid Cycle…
• Pyruvate is broken down into three molecules of CO2
(includes the CO2 produced during the conversion to Acetyl
CoA)
• The cycle oxidizes organic fuel derived from pyruvate,
generating
– 1 ATP (via substrate-level phosphorylation)
– 3 NADH (contains most of the chemical energy)
– 1 FADH2 (flavin adenine dinucleotide acts as a electron shuttle)
• NADH and FADH2 can then shuttle their high energy electrons to
the ETC

23. Fig. 9-11
Pyruvate
CO2
NAD+
CoA
NADH
+ H+ Per 1 pyruvate:
Acetyl CoA
CoA
•3 CO2
•3 NADH
CoA
•1 ATP
•1 FADH
Per 2 pyruvates or
1 glucose:
Citric
acid •6 CO2
cycle 2 CO2 •6 NADH
•2 ATP
FADH2 3 NAD+
•2 FADH
FAD 3 NADH
+ 3 H+
ADP + P i
ATP

24. During oxidative phosphorylation, chemiosmosis
couples electron transport to ATP synthesis
• Following glycolysis and the citric acid cycle, NADH and
FADH2 account for most of the energy extracted from food
• These two electron carriers donate electrons to the electron
transport chain, which powers ATP synthesis via oxidative
phosphorylation
• 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

25. The ETC
NADH
Electron carriers alternate 50
2 e–
between reduced and NAD+
FADH2
oxidized states as they
2 e– FAD
accept and donate
Multiprotein
electrons. Ι
Electronegativity
40 FMN FAD complexes
Fe•S Fe•S Ι
Free energy (G) relative to O2 (kcal/mol)
Each component of the Ι
Q
chain becomes reduced ΙΙ
Cyt b Ι
when it accepts electrons
Fe•S
from its uphill neighbor, 30
Cyt c1
which is less IV
Cyt c
electronegative.
Cyt a
Cyt a3
The carrier then returns to 20
its oxidized form as it
passes electrons downhill
to its more electronegative
neighbor. 2 e–
10
(from NADH
The ETC eases the fall of or FADH2)
electrons from food to
oxygen, breaking a large
free-energy drop into 0 2 H+ + 1/2 O2
smaller steps that release
energy in manageable
amounts.
H2O
Fig. 9-13

26. Chemiosmosis: The Energy-Coupling Mechanism
• Electron transfer in the ETC 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
• ATP synthase uses the exergonic flow of H+ to drive phosphorylation of
ADP
• This is an example of chemiosmosis, the use of energy in a H+ gradient
to drive cellular work
• The energy stored in a H+ gradient across a membrane couples the
redox reactions of the electron transport chain to ATP synthesis
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

27. Chemiosmosis couples the ETC to ATP synthesis
H+
H +
H+
H+
Protein Cyt c
complex
of electron
carriers
ΙV
Q
Ι ΙΙ
Ι ATP
synthase
ΙΙ
2 H+ + 1/2O2 H2O
FADH2
FAD
NADH NAD+
ADP + P i ATP
(carrying electrons
from food)
H+
1 Electron transport chain Electron transport and
pumping of protons (H+), which create an H+ gradient 2 Chemiosmosis ATP synthesis
powered by the flow of H+
across the membrane
back across the membrane
Oxidative phosphorylation
Fig. 9-16

28. An Accounting of ATP Production by Cellular
Respiration
• During cellular respiration, most energy flows in
this sequence:
glucose → NADH → ETC→ chemiosmosis →
ATP
• One NADH can produce about 3 ATP
• About 40% of the energy in a glucose molecule
is transferred to ATP during cellular respiration,
making about 38 ATP
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

29. ATP yield/molecule of glucose at each stage of cellular respiration
CYTOSOL Electron shuttles MITOCHONDRION
span membrane 2 NADH
or
2 FADH2
2 NADH 2 NADH 6 NADH 2 FADH2
Glycolysis Oxidative
2 2 Citric phosphorylation:
Glucose Pyruvate Acetyl acid electron transport
CoA cycle and
chemiosmosis
+ 2 ATP + 2 ATP + about 32 or 34 ATP
Maximum About
per glucose: 36 or 38 ATP
Fig. 9-17

30. Fermentation and anaerobic respiration enable cells
to produce ATP without the use of oxygen
• Most cellular respiration requires O2 to produce ATP
• Glycolysis can produce ATP with or without O2 (in
aerobic or anaerobic conditions)
• In the absence of O2, glycolysis couples with fermentation
or anaerobic respiration to produce ATP
• Anaerobic respiration uses an electron transport chain
with an electron acceptor other than O2, for example sulfate
• Fermentation uses phosphorylation instead of an electron
transport chain to generate ATP
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31. Types of Fermentation
• Two common types are alcohol fermentation and lactic
acid fermentation
• In alcohol fermentation, pyruvate is converted to ethanol
in two steps, with the first releasing CO2
– used in brewing, winemaking, and baking
• In lactic acid fermentation, pyruvate is reduced to NADH,
forming lactate as an end product, with no release of CO 2
– used to make cheese and yogurt
– Human muscle cells use lactic acid fermentation to generate ATP
when O2 is scarce

32. Fig. 9-18
2 ADP + 2 Pi 2 ATP
Glucose Glycolysis
Alcohol
fermentation 2 Pyruvate
produces 2 NAD+ 2 NADH 2 CO2
ethanol + 2 H+
2 Ethanol 2 Acetaldehyde
2 ADP + 2 Pi 2 ATP
Glucose Glycolysis
Lactic acid
fermentation
2 NAD+ 2 NADH
produces + 2 H+
lactate 2 Pyruvate
2 Lactate

33. Fig. 9-19
Glucose
Glycolysis
CYTOSOL
Pyruvate
No O2 present: O2 present:
Fermentation Aerobic cellular
respiration
MITOCHONDRION
Ethanol Acetyl CoA
or
lactate
Citric
acid
cycle

34. Fermentation and Aerobic Respiration Compared
• Both processes use glycolysis to oxidize
glucose and other organic fuels to pyruvate
• The processes have different final electron
acceptors: an organic molecule (such as
pyruvate or acetaldehyde) in fermentation and
O2 in cellular respiration
• Cellular respiration produces 38 ATP per
glucose molecule; fermentation produces 2
ATP per glucose molecule
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings