Download Cellular respiration

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
Overview: Life Is Work
• Living cells
– Require transfusions of energy from outside
sources to perform their many tasks
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The giant panda
– Obtains energy for its cells by eating plants
Figure 9.1
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Energy
– Flows into an ecosystem as sunlight and
leaves as heat
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
ATP
powers most cellular work
Figure 9.2
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Heat
energy
Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is
exergonic (releasing energy)
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One catabolic process, fermentation
– Is a partial degradation of sugars that occurs
without oxygen
– Aerobic- with oxygen
– Anaerobic- without oxygen
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Cellular respiration
– Is the most common and efficient breakdown
of energy from food
– Consumes (takes) oxygen and organic
molecules such as glucose
– Yields (produces) ATP
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To keep working
– Cells must regenerate ATP
– ATP- The energy currency for cells to do work
(grow, divide, function)
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Redox Reactions: Oxidation and Reduction
• Catabolic pathways yield energy
– Due to the transfer of electrons
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Organic Fuel Molecules During Cellular
Respiration
• During cellular respiration:
C6H12O6 + 6O2
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6CO2 + 6H2O + Energy
The Stages of Cellular Respiration: A Preview
• Respiration is a cumulative function of three
metabolic stages
– Glycolysis
– Krebs cycle (also known as The citric acid
cycle)
– Electron Transport Chain
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Stages and Locations of Cellular Respiration
– Glycolysis (doesn’t require oxygen) happens
in the cytoplasm of cell
– Krebs cycle/ Citric Acid Cycle (Needs
oxygen) happens in the fluid of mitochondria
– Electron Transport Chain/ Oxidative
phosphorylation (needs oxygen) happens in
the mitochondria membrane
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Glycolysis -> Krebs Cycle -> Electron Transport Chain
• STEP 1: Glycolysis
– Breaks down glucose into two molecules of
pyruvate
– Glucose -- pyruvate
• STEP 2: Krebs Cycle/ The citric acid cycle
– Completes the breakdown of glucose
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Glycolysis -> Krebs Cycle -> Electron Transport Chain
• STEP 3: Electron Transport Chain
– Is driven by the electron transport chain
– Generates ATP (energy currency)
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An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
re 9.6
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Substrate-level
phosphorylation
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ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
Concept 9.2: Glycolysis harvests energy by
oxidizing glucose to pyruvate
Glucose
Goes in
• Glycolysis
– Means “splitting of sugar”
– Breaks down glucose into pyruvate
– Occurs in the cytoplasm of the cell
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Pyruvate
ATP
Come out
Krebs Cycle/ Citric Acid Cycle
• The citric acid cycle completes the energyyielding oxidation of organic molecules
• The citric acid cycle
– Takes place in the matrix of the mitochondrion
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An overview of the citric acid cycle/ Krebs Cycle
Pyruvate
goes in
Pyruvate
(from glycolysis,
2 molecules per glucose)
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylatio
n
ATP
CO2
CoA
NADH
+ 3 H+ Acetyle CoA
CoA
CoA
FADH2
ATP
NADH
CO2
Citric
acid
cycle
2 CO2
3 NAD+
FADH2
FAD
3 NADH
+ 3 H+
ADP + P i
Come out
ATP
Figure 9.11
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Electron Transport Chain  ATP synthesis
• Concept 9.4: During oxidative phosphorylation,
chemiosmosis couples electron transport to
ATP synthesis
• NADH and FADH2 (Products of Krebs Cycle)
– Donate electrons in the electron transport
chain which powers ATP synthesis
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At the end of the Electron Transport Chain
– Electrons are passed to oxygen, forming water
NADH
50
Free energy (G) relative to O2 (kcl/mol)
FADH2
40
I
FMN
Multiprotein
complexes
FAD
Fe•S
Fe•S
II
O
III
Cyt b
30
Fe•S
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
20
10
0
Figure 9.13
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2 H + + 12
O2
H2 O
There are three main processes in this metabolism
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH
Glycolysis
Glucose
2
Pyruvate
6 NADH
Citric
acid
cycle
2
Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
+ 2 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by substrate-level by oxidative phosphorylation, depending
on which shuttle transports electrons
phosphorylation
from NADH in cytosol
About
36 or 38 ATP
Figure 9.16
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There are three main processes in this metabolism
SIMPLIFIED!
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH
Glycolysis
Glucose
2
Pyruvate
6 NADH
Citric
acid
cycle
2
Acetyl
CoA
+ 2 ATP
+ 2 ATP
Maximum per glucose:
About
36 or 38 ATP
Figure 9.16
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2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
About 40% of the energy in a glucose molecule
– Is transferred to ATP during cellular
respiration, making between 36-38 ATP
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Concept 9.5: Fermentation- some cells can produce
ATP without the use of oxygen – (anaerobic)
• Cellular respiration
– Relies on oxygen to produce ATP
• Fermentation
– Cells can still produce ATP in the absence of
Oxygen
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Glycolysis
– Can produce ATP with or without oxygen, in
aerobic or anaerobic conditions
– Couples with fermentation to produce ATP
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Types of Fermentation
• Alcohol Fermentation- Happens with yeast
• Lactic Acid Fermentation- happens in our
bodies after exercise.
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In alcohol fermentation
– Pyruvate is converted to ethanol in two steps,
one of which releases CO2
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During lactic acid fermentation
– Pyruvate is reduced directly to NADH to form
lactate as a waste product
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Alcohol Fermentation -> ethanol
Lactic acid Fermentation -> lactic acid
2 ADP + 2
P1
2 ATP
O–
C O
Glucose
Glycolysis
C O
CH3
2 Pyruvate
2 NADH
2 NAD+
H
2 CO2
H
H C OH
C O
CH3
CH3
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
2 ADP + 2
Glucose
P1
2 ATP
Glycolysis
O–
C O
C O
O
2 NAD+
2 NADH
C O
H
C OH
CH3
2 Lactate
Figure 9.17
(b) Lactic acid fermentation
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CH3
Fermentation and Cellular Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other
organic fuels to pyruvate
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Fermentation vs. Cellular Respiration
• Cellular respiration
– Produces more ATP
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Pyruvate is a key juncture in catabolism
• (Catabolism is the metabolic breakdown of complex
molecules into simpler ones, often resulting in a release of
Glucose
energy.)
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Figure 9.18
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Acetyl CoA
Citric
acid
cycle
The Evolutionary Significance of Glycolysis
• Glycolysis
– Occurs in nearly all organisms
– Probably evolved in ancient prokaryotes before
there was oxygen in the atmosphere
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Biosynthesis (Anabolic Pathways)
• The body
– Uses small molecules to build other
substances
• These small molecules
– May come directly from food or through
glycolysis or the citric acid cycle
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