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Chapter 9
Cellular Respiration:
Harvesting Chemical Energy
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Introduction
• Overview: Life Is Work
• Living cells
– Require transfusions of
energy from outside
sources to perform their
many tasks
• Energy
– Flows into an
ecosystem as sunlight
and leaves as heat
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Big Picture
• Cells harvest chemical energy stored in organic
molecules and use it to generate ATP.
• ATP is generated through the transfer of
electrons (in the form of H+) from organic
molecules.
• Two types of Energy Harvesting processes
– Aerobic - Cellular Respiration
– Anaerobic – Fermentation, Lactic Acid
production
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
I. How is ATP produced?
•
Big Idea: Transfer of electrons releases Energy
•
Key Question: How do electrons get transferred?
A. Redox Reactions: Oxidation and Reduction
1.
Definitions
a) Oxidation – loss of e from a substance
b) Reduction – addition of e to a substance
c)
Oxidizing Agent – e acceptor
d) Reducing Agent – e donor
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B. Redox reactions in cellular respiration
1.
a) Glucose gives up e
b) Oxygen accepts electrons
2. e in glucose have a lot of potential E which they
give off when transferred to oxygen
a) e are transferred in steps, so E is released gradually.
3. Carbs and Fat have a lot of H atoms to free
up…therefore they store a lot of E
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C. Role of NAD+ and Electron Transport Chain
1. NAD+ is the main e transfer molecule in cellular
respiration
(It is an oxidizing agent since it accepts e)
•
Dehydrogenases (enzymes) remove a pair of H
atoms (2 e) and transfers both e and one proton to
NAD+ making NADH
•
NADH then transfers e to electron transport chain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2. Electron Transport Chain (ETC)
a) Pathway of several enzymes which pass e
from one to another.
1) Everytime e moves from one enzyme to
another, energy is released and used to
make ATP
b) ETC located in the inner membrane of
eukaryotes
1) Plasma membrane in prokaryotes
c) Oxygen is the final acceptor of e in ETC
(making H2O)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3. Why use the ETC?
a) Stepwise release of E is more controlled
and better able to be harvested.
b) Without ETC, too much E would be
released at one time and could not be used
as efficiently.
H2 + 1/2 O2
Free energy, G
Explosive
release of
heat and
light
energy
Figure 9.5 A
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
H2O
(a)
Uncontrolled
reaction
BAD!!!!
D. The Stages of Cellular Respiration: A Preview
1. Respiration is a cumulative function of three
metabolic stages
a) Glycolysis
b) The citric acid cycle
c) Oxidative phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
II. Glycolysis
A. Sole purpose is to produce PYRUVATE
1. Occurs in cytosol
2. Breaks down glucose into two molecules of
pyruvate (3 C sugars)
3. Two Stages
a) Energy investment stage
1) 2 ATP used
b) Energy payoff stage
1) 4 ATP produced (Net 2 ATP)
2) 2 NADH produced
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III. The Citric Acid Cycle
• Citric Acid Cycle takes place in the MITOCHONDRION
• Prior to entering Citric Acid Cycle, Acetyl CoA is added to
the pyruvate molecule
Addition of CoA
group makes a
highly reactive
molecule
Can give off a
lot of Energy
(YAY!)
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
O–
S
CoA
C
O
2
C
C
O
O
1
3
CH3
Pyruvate
Transport protein
Figure 9.10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CH3
Acetyle CoA
CO2
Coenzyme A
Energy Extraction
Net Energy Production
•8 NADH
•2 ATP
•2 FADH2 (another e
carrier like NAD+)
*Note – Carbon skeleton is
reused during the next
cycle
So far only 4 ATP
produced total in whole
cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
IV. Oxidative Phosphorylation (ETC)
A. Electron Transport Chain
1. Thousands of copies in mitochondrion
2. Contains 4 multi-subunit complexes
a) As e passed from complex to complex the
alternate between reduced and oxidized states
b) 10 e carrier molecules in the ETC (most are
cytochromes which contain an Fe group that
accepts and gives off the e)
c) Last cytochrome passes the e to oxygen
making H2O
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3.
e are transported into the space between the inner
and outer membrane of the mitochondion
a) Generates a H+ gradient (high in between
membranes, low inside mitocondrion
b) When e return to the inside of the mitochondrion,
ATP is produced (details soon)
4.
Role of NADH and FADH2
a) Donate electrons to the electron transport chain
a) FADH2 does not generate as much E because
it is a lower energy level carrier
b) Eventually powers ATP synthesis via oxidative
phosphorylation
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B. Chemiosmosis: The EnergyCoupling Mechanism
*oxidative phosphorylation
*ATP production (finally)
1.
ATP synthase
a) Is the enzyme that
actually makes ATP
b) H+ flows from high
concentration to low
concentration
(passive transport)
c) Chemiosmosis –
flow of H+ across a
membrane
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• Electron transport chain and Chemiosmosis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C. An Accounting of ATP Production by Cellular
Respiration
1. About 40% of the energy in a glucose
molecule
a) Is transferred to ATP during cellular
respiration, making approximately 38 ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
V. Anaerobic Respiration
A. Very Similar to Cellular Respiration
1. Have an ETC
a) Difference is that O is not the final e acceptor
1) Final acceptors: N, S, and C
2) All of these produce far less E for ATP
production.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
VI. Fermentation
A. Basic Facts
1. Produces energy without O or ETC.
2. Beginning is the same as cellular respiration
a) Glycolysis changes glucose to pyruvate
b) Pyruvate is then used to accept e from NADH
1) This free NAD+ so it can go back and
produce more ATP in glycolysis.
B. Types of Fermentation
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Alcoholic Fermentation
Pyruvate changed to
acetaldehyde.
Acetaldehyde accepts 2H
and becomes Ethanol.
Lactic Acid Fermentation
Pyruvate changed directly
to lactic acid.
In this process, pyruvate
accepts 2H.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C. Fermentation and Cellular Respiration Compared
1.
Both use glycolysis to oxidize glucose and other
organic fuels to pyruvate
a) Generates 2 ATP
b) Both use NAD as electron acceptor
2.
Recycling NAD is different (how NAD gives up e)
a) Cellular Respiration – NAD freed up via ETC (more
ATP produced)
b) Fermentation – pyruvate eventually accepts e. (No
more ATP produced)
3.
Result
a) cellular respiration - 38 ATP
b) Fermentation – 2 ATP
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• Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Figure 9.18
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Acetyl CoA
Citric
acid
cycle
VI. Metabolic Connections
A. Versatility of Catabolism
1. While glucose is ideal, it can use many other
molecules in cellular respiration.
a) Proteins, fatty acids, disaccharides,
polysaccharides
2. Molecules either converted to glucose or an
intermediate form in cellular respiration.
a) Amino acids must have amino groups removed
via deamination.
3. Beta oxidation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3. Beta Oxidation
a) Breaks fatty acids into glycerol and multiple
two carbon molecules
b) The 2-C molecules are converted to Acetyl
CoA and enter the citric acid cycle.
c) Example
18 C fatty acid = 9 acetyl CoA
Total of 216 ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
B. Biosynthesis (Anabolic Pathways)
1. The body uses small molecules to build
other substances
a) Amino acids – proteins
b) Carbon fragments for larger molecules
2. These small molecules may come directly
from food or through glycolysis or the citric
acid cycle (intermediates)
a) We can make half of all amino acids from
citric acid cycle compounds.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C. Regulation of Cellular Respiration
Cell doesn’t waste energy making stuff if doesn’t need
1. Feedback Inhibition
a) End product inhibits an enzyme at the
beginning of the process.
1) Excess of ATP slows Cellular Respiration
b) Example: phosphofructokinase (allosteric
enzyme)
1) Inhibited by ATP and citrate (1st step citric
acid cycle)
2) Stimulated by AMP (made from ADP)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings