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Chapter 6
How Cells Harvest Chemical
Energy
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
How Is a Marathoner Different from a Sprinter?
• Muscles in human legs contain two different
types of muscle fibers
– Marathoners have more slow-twitch
fibers, which perform better in endurance
exercises
– Sprinters have more fast-twitch fibers,
which perform best in short bursts of
intense activity
–
Chickens can relate
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The different types of muscle fibers use
different processes for making ATP
– Slow-twitch fibers undergo aerobic (in the
presence of O2) respiration
– Fast-twitch fibers undergo anaerobic (in the
absence of O2) respiration
• Cellular respiration is the process by which
cells produce energy aerobically
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
INTRODUCTION TO CELLULAR RESPIRATION
6.1 Photosynthesis and cellular respiration
provide energy for life
• All living organisms require energy to maintain
homeostasis, to move, and to reproduce
• Photosynthesis converts energy from the sun to
glucose and O2
• Cellular respiration breaks down glucose and
releases energy in ATP
• Energy flows through an ecosystem; chemicals
are recycled
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-1
Sunlight energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2
Glucose
H2O
O2
Cellular respiration
in mitochondria
ATP
(for cellular work)
Heat energy
D. Energy and Exercise (refer to activity sheet)
E. Comparing Photosynthesis and Cellular Respiration
Photosynthesis
Function
Cellular Respiration
Energy Capture
Energy Release
Chloroplasts
Mitochondria
H2O and CO2
C6H12O6 and O2
C6H12O6 and O2
H2O and CO2
Location
Reactants
Products
Equation
6H2O + 6CO2 → C6H12O6 + 6O2
C6H12O6 + 6O2 → 6H2O + 6CO2
6.2 Breathing supplies oxygen to our cells and
removes carbon dioxide
• Breathing and cellular respiration are closely
related
–
Breathing brings O2 into the body from the
environment
–
O2 is distributed to cells in the bloodstream
–
In cellular respiration, mitochondria use O2
to harvest energy and generate ATP
–
Breathing disposes of the CO2 produced as
a waste product of cellular respiration
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-2
O2
Breathing
CO2
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
Cellular Respiration
Glucose  O2
CO2  H2O  ATP
6.3 Cellular respiration banks energy in ATP
molecules
• The reactants O2 and glucose regroup to form
the products CO2 and H2O
• Energy from glucose is released and stored in
ATP
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-3
Glucose
Oxygen gas
Carbon
dioxide
Water
Energy
CONNECTION
6.4 The human body uses energy from ATP for
all its activities
• The body needs a continual supply of energy to
maintain basic functioning
• In addition, ATP supplies energy (kilocalories)
for voluntary activities
• An average adult human needs about 2,200
kcal of energy each day
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
6.5 Cells tap energy from electrons “falling” from
organic fuels to oxygen
• The energy available to a cell is contained in
the arrangement of electrons in chemical bonds
• Electrons lose potential energy when they “fall”
from organic compounds to oxygen during
cellular respiration
• Each step of the “fall” involves paired
oxidation–reduction (redox) reactions
– Oxidation: loss of electrons (in atoms)
– Reduction: addition of electrons
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• NADH delivers electrons to a series of electron
carriers in an electron transport chain
• As electrons move from carrier to carrier, their
energy is released in small quantities
Electron flow
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• The redox reactions of cellular respiration
– Glucose loses electrons (in H atoms) and
becomes oxidized
– O2 gains electrons (in H atoms) and
becomes reduced
– Along the way, the electrons lose potential
energy, and energy is released
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Glucose gives up energy as it is oxidized
Loss of hydrogen atoms
Energy
Glucose
Gain of hydrogen atoms
Figure 6.4
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The redox reactions that break down glucose
involve an enzyme and a coenzyme
– The enzyme dehydrogenase removes
electrons (in H atoms) from fuel
molecules (oxidation)
– The electrons are transferred to the
coenzyme NAD+, which is converted to
NADH (reduction)
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Oxidation
Dehydrogenase
Reduction
NAD
NADH
2H
2H


2
e
(carries
2 electrons)
H
– NADH passes electrons to an electron
transport chain
•
As electrons “fall” from carrier to
carrier and finally to O2, energy is
released in small quantities
•
The energy released is used by the
cell to make ATP
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-5c
NADH
ATP
NAD
2e
Controlled
release of
energy for
synthesis
H
of ATP
2e
2
1
2
H
H2O
O2
Two mechanisms generate ATP
http://www.sp.uconn.edu/~terry/Common/respiration.html
• Cells use the energy
released by “falling”
electrons to pump
H+ ions across a
membrane
• The energy of the
gradient is
harnessed to
make ATP by the
process of
chemiosmosis
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
High H+
concentration
ATP synthase
uses gradient
energy to
make ATP
Membrane
Electron
transport
chain
ATP
synthase
Energy from
Low H+
concentration
Figure 6.7A
• ATP can also be
made by
transferring
phosphate groups
from organic
molecules to ADP
-This process
is called
substrate-level
phosphorylation
Enzyme
Adenosine
Organic molecule
(substrate)
Adenosine
New organic molecule
(product)
Figure 6.7B
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Overview of Glucose Breakdown
• The overall equation for the complete
breakdown of glucose is:
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
• The main stages of glucose metabolism are:
• Glycolysis
• Cellular respiration
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• An overview of cellular respiration
High-energy electrons
carried by NADH
GLYCOLYSIS
Glucose
Pyruvic
acid
Cytoplasmic
fluid
Figure 6.8
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
Mitochondrion
Flowchart
Section 9-2
Cellular Respiration
Glucose
(C6H1206)
+
Oxygen
(02)
Glycolysis
Krebs
Cycle
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Electron
Transport
Chain
Carbon
Dioxide
(CO2)
+
Water
(H2O)
STAGES OF CELLULAR RESPIRATION AND
FERMENTATION
6.6 Overview: Cellular respiration occurs in three
main stages
Stage 1: Glycolysis
• Occurs in the cytoplasm
• Breaks down glucose into pyruvate, producing
a small amount of ATP
Glucose
Pyruvic
acid
• Stage 2: The citric acid cycle
Acetyl CoA
KREBS
CYCLE
KREBS
CYCLE
2 CO2
–
Takes place in the mitochondria
–
Completes the breakdown of glucose, producing
CO2 and a small amount of ATP
–
Supplies the third stage of cellular respiration with
electrons
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Stage 3: Oxidative phosphorylation
– Occurs in the mitochondria
– Uses the energy released by electrons
“falling” down the electron transport
chain to pump H+ across a membrane
– Harnesses the energy of the H+ gradient
through chemiosmosis, producing ATP
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-6
NADH
High-energy electrons
carried by NADH
FADH2
NADH
and
GLYCOLYSIS
Glucose
CITRIC ACID
CYCLE
Pyruvate
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
Cytoplasm
Mitochondrion
CO2
CO2
ATP
Substrate-level
phosphorylation
ATP
ATP
Substrate-level
phosphorylation
Oxidative
phosphorylation
6.7 Glycolysis harvests chemical energy by
oxidizing glucose to pyruvate
• Glycolysis splits sugar molecules in the
cytoplasm
– Starts with a single 6-carbon molecule of
glucose
– Ends with two 3-carbon molecules of
pyruvate
– Produces two molecules of ATP in the
process
Animation: Glycolysis
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-7a
2
NAD
2
NADH
2
Glucose
H
2 Pyruvate
2 ADP
2
P
2
ATP
• Glycolysis produces ATP by substrate-level
phosphorylation
– An enzyme transfers a phosphate group
from an organic molecule to ADP
– A small amount of ATP is produced
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-7b
Enzyme
P
P
P
Adenosine
ADP
ATP
P
Organic molecule
(substrate)
P
• Details of
glycolysis
– A fuel
molecule is energized,
using ATP.
Glucose
1Steps
3
Step
PREPARATORY
PHASE
(energy investment)
1
Glucose-6-phosphate
2
Fructose-6-phosphate
3
Fructose-1,6-diphosphate
4
Step
A six-carbon
intermediate splits into
two three-carbon
intermediates.
4
Glyceraldehyde-3-phosphate
(G3P)
5
5
Step
A redox
reaction generates
NADH.
6
Steps6 –9 ATP
and pyruvic acid
are produced.
ENERGY PAYOFF
PHASE
1,3-Diphosphoglyceric acid
(2 molecules)
7
3-Phosphoglyceric acid
(2 molecules)
8
2-Phosphoglyceric acid
(2 molecules)
2-Phosphoglyceric acid
(2 molecules)
9
Figure 6.9B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin
Cummings
Pyruvic acid
(2 molecules
per glucose molecule)
6.10 Pyruvic acid is chemically groomed for the
Krebs cycle
• Each pyruvic acid molecule is broken down to
form CO2 and a two-carbon acetyl group, which
enters the Krebs cycle
NAD
NADH

H
CoA
Pyruvate
Acetyl CoA
(acetyl coenzyme A)
CO2
Coenzyme A
6.11 The citric acid cycle completes the oxidation
of organic fuel, generating many NADH and
FADH2 molecules
• For each turn of the citric acid cycle
– Two CO2 molecules are released
– The energy yield is one ATP, three
NADH, and one FADH2
Animation: Citric Acid Cycle
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-9a
Acetyl CoA
CoA
CoA
2 CO2
CITRIC ACID CYCLE
3
FADH2
3
FAD
NAD
NADH

3 H
ATP
ADP

P
LE 6-9b
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
Citrate
NADH
 H
CO2
NAD
leaves
cycle
NAD
CITRIC ACID CYCLE
Malate
NADH
ADP
FADH2

P
ATP
Alpha-ketoglutarate
FAD
CO2
Succinate
NADH
 H
NAD
leaves
cycle
 H
• Details of the citric acid cycle
– The 2-carbon acetyl part of acetyl CoA is
oxidized
– The two carbons are added to a
4-compound, forming citrate
– Through a series of redox reactions, two
carbons are removed from citrate as CO2
and the 4-carbon compound is regenerated
– The energy-rich molecules ATP, NADH,
and FADH2 are produced
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
ETC/chemiosmosis
Oxidative phosphorylation
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Chemiosmosis
•
Flow of hydrogen ions provides energy to link
32-34 molecules of ADP with phosphate,
forming 32-34 ATP
•
ATP then diffuses out of mitochondrion and
used for energy-requiring activities in the cell
Link: ETC and chemiosmosis
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-10
H
H
H
Protein
complex
Intermembrane
space
H
H
Electron
carrier
H
H
H
H
ATP
synthase
Inner
mitochondrial
membrane
FADH2
Electron
flow
NADH
Mitochondrial
matrix
FAD
NAD
H
1
2
O2
 2 H
H
H
H2O
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
ADP
 P
ATP
H
Chemiosmosis
CONNECTION
6.11 Certain poisons interrupt critical events in
cellular respiration
• Rotenone, cyanide, and carbon monoxide block
parts of the electron transport chain
• Oligomycin blocks the passage of H+ through
ATP synthase
• Uncouplers such as DNP destroy the H+
gradient by making the membrane leaky to H+
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-11
Rotenone
Cyanide,
carbon monoxide
H+
H+
H+
Oligomycin
H+
H+
H+ H+ H+
H+
ATP
synthase
DNP
FAD
FADH2
NAD
NADH
1
2
+
O2 + 2 H+
H+
H+
H2O
ADP + P
ATP
H+
Electron Transport Chain
Chemiosmosis
6.12 Review: Each molecule of glucose yields
many molecules of ATP
• Glycolysis and the citric acid cycle together
yield four ATP per glucose molecule
• Oxidative phosphorylation, using electron
transport and chemiosmosis, yields 34 ATP per
glucose
• These numbers are maximums
– Some cells may lose a few ATP to NAD+ or
FAD shuttles
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-12
LINK:CELLULAR RESPIRATION VIDEO-CALIFORNICATION
Electron shuttle
across membrane
Cytoplasm
2 NADH
Mitochondrion
2
NADH
(or 2 FADH2)
2 NADH
6
Glucose
2 Acetyl
CoA
 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
2 FADH2
CITRIC ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
 2 ATP
 about 34 ATP
by substrate-level
phosphorylation
by oxidative
phosphorylation
GLYCOLYSIS
2
Pyruvate
NADH
About
38 ATP
C. The Totals Per Glucose molecule
3 ATP
***note: each NADH produces __
2 ATP
each FADH2 produces __
Click on ATP synthesis and play the first one only
http://www.wiley.com/legacy/college/boyer/0470003790/animations/electron_transport/electron_transport.htm
LOCATION
ATP
NADH
FADH2
BYPRODUCTS
cytoplasm
2
2
0
------
KREBS CYCLE:
Pyruvate oxidation
→
matrix
0
2
0
Carbon
dioxide
Energy Extraction
→
matrix
2
6
2
Carbon
dioxide
Inner
Membrane
(Cristae)
34
0
0
water
GLYCOLYSIS
ELECTRON
TRANSPORT
CHAIN
TOTALS (net)
36
2
-2 ATP (transport of pyruvic acid into mitochondria)
6.13 Fermentation is an anaerobic alternative to
cellular respiration
• Fermentation
– Generates two ATP molecules from
glycolysis in the absence of oxygen
– Recycles NADH to NAD+ anaerobically
• Muscle cells use lactic acid fermentation
– NADH is oxidized to NAD+ as pyruvate is
reduced to lactate
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-13a
2
NAD
NADH
2
2
NADH
2
NAD
GLYCOLYSIS
2 ADP

2
P
2
ATP
2 Pyruvate
Glucose
2 Lactate
• Alcohol fermentation occurs in brewing, wine
making, and baking
– NADH is oxidized to NAD+ while converting
pyruvate to CO2 and ethanol
Animation: Fermentation Overview
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-13b
2
NAD
NADH
2
2
NADH
2
NAD
GLYCOLYSIS
2 ADP
Glucose
2

2
P
2
2
ATP
2 Pyruvate
CO2
released
2 Ethanol
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Strict anaerobes
– Require anaerobic conditions to generate
ATP by fermentation
– Are poisoned by oxygen
• Facultative anaerobes
– Can make ATP by fermentation or
oxidative phosphorylation depending on
whether O2 is available
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
COMPARISON OF FERMENTATION TO
CELLULAR REPIRATION
Lactic Acid
glucose
Alcoholic
glucose
Cellular respiration
glucose
glycolysis
(pyruvic acid)
glycolysis
(pyruvic acid)
carbon dioxide
carbon dioxide
lactic acid
alcohol
water
2 ATP
2 ATP
38 ATP
glycolysis
(pyruvic acid)
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
INTERCONNECTIONS BETWEEN MOLECULAR
BREAKDOWN AND SYNTHESIS
6.14 Cells use many kinds of organic molecules
as fuel for cellular respiration
Cells use three main kinds of food molecules to
make ATP
• Carbohydrates
– Hydrolyzed by enzymes to glucose,
which enters glycolysis
• Proteins
– Digested to constituent amino acids, which
are transformed into various compounds
– Become intermediates in glycolysis or the
citric acid cycle
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Fats
– Digested to glycerol and free fatty acids
• Glycerol becomes an intermediate in
glycolysis
• Fatty acids are broken into 2-carbon
fragments that enter the citric acid
cycle as acetyl CoA
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-14
Food, such as
peanuts
Fats
Carbohydrates
Proteins
Glycerol Fatty acids
Sugars
Amino acids
Amino groups
Glucose
G3P
Pyruvate
Acetyl
CoA
GLYCOLYSIS
ATP
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
6.15 Food molecules provide raw materials for
biosynthesis
• Some raw materials from food can be incorporated
directly into an organism’s molecules
• Cells can also make molecules not found in food
–
Intermediate compounds of glycolysis and
the citric acid cycle act as raw materials
–
Biosynthetic pathways consume ATP rather
than generate it
–
Biosynthesis is not always the direct reverse
of breakdown pathways
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LE 6-15
ATP needed to drive biosynthesis
ATP
CITRIC
ACID
CYCLE
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvate
G3P
Glucose
Amino
groups
Amino acids
Proteins
Fatty acids
Glycerol
Fats
Cells, tissues, organisms
Sugars
Carbohydrates
6.16 The fuel for respiration ultimately comes
from photosynthesis
• All organisms can harvest energy from organic
molecules
• Plants can also make molecules from inorganic
sources by photosynthesis
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings