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Chapter 7
Harvesting Energy:
Glycolysis and
Cellular Respiration
Lectures by
Gregory Ahearn
University of North Florida
Copyright © 2009 Pearson Education, Inc.
7.1 What Is The Source Of A Cell’s Energy?
 The energy for cellular activities is stored until use in
_________ of molecules such as carbohydrates and fats.
 In order to be used, stored energy is transferred to the
bonds of energy-carrier molecules such as adenosine
triphosphate (ATP).
 _________ is a key energy-storage molecule, and energy
stored in this molecule is harvested to power many
biological processes in cells.
Copyright © 2009 Pearson Education Inc.
7.1 What Is The Source Of A Cell’s Energy?
 Photosynthesis is the ultimate source of cellular
energy.
 Photosynthetic cells capture and store sunlight energy,
and this energy is later used by cells.
 These cells can be the photosynthetic organisms
themselves, or can be other organisms that directly or
indirectly consume photosynthesizers.
Copyright © 2009 Pearson Education Inc.
7.1 What Is The Source Of A Cell’s Energy?
 ___________ metabolism and ____________ are
complementary processes.
 The products of each reaction provide reactants
for the other.
 The symmetry is apparent by comparing the equations
that describe each process.
• Photosynthesis:
6 CO2 + 6H2O + sunlight energy  C6H12O6 + 6 O2
• Complete glucose metabolism:
C6H12O6 + 6O2  6 CO2 + 6 H20 + ATP + heat energy
Copyright © 2009 Pearson Education Inc.
7.2 How Do Cells Harvest Energy From
Glucose?
 Glucose metabolism occurs in stages; the
first stage is glycolysis.
• Glycolysis occurs in the ___________ of cells.
• Glucose (a six-carbon sugar) is split into two
three-carbon _______ molecules.
• The split releases a small amount of energy that is
used to make _____ ATP molecules.
Copyright © 2009 Pearson Education Inc.
(cytoplasmic fluid)
C C C C C C
glucose
Glycolysis
2
ATP
2 C C C
2 C C C
pyruvate
lactate
or
Fermentation
2 C C +2 C
ethanol
CO2
Cellular respiration
C C
2 acetyl CoA
4 C CO2
C 2 CO2
Krebs
cycle
2
electron
carriers
H2O
Electron transport chain
ATP
intermembrane
compartment
32 or 34 ATP
(mitochondrion)
O2
Copyright © 2009 Pearson Education Inc.
Fig. 7-1
7.2 How Do Cells Harvest Energy From
Glucose?
 Pyruvate produced by glycolysis is further processed in
the second stage, called cellular ______________.
 Cellular respiration occurs in the _______________.
 Cellular respiration breaks pyruvate down to CO2 and H20,
yielding 34 or 36 ATP molecules.
 ____________ is needed for cellular respiration to
proceed.
Copyright © 2009 Pearson Education Inc.
7.2 How Do Cells Harvest Energy From
Glucose?
 When oxygen is not available, the second stage of glucose
metabolism is ____________.
 In the absence of oxygen, pyruvate remains in the
cytoplasm.
 Cytoplasmic pyruvate may be converted to _________ or
_________ by fermentation.
 Fermentation does not produce additional ATP
energy.
Copyright © 2009 Pearson Education Inc.
7.3 What Happens During Glycolysis?
 Glycolysis splits one molecule of glucose into two
molecules of pyruvate.
 During glycolysis, one molecule of glucose yields two
ATP and two molecules of the electron carrier
nicotinamide adenine dinucleotide (NADH).
 Glycolysis involves two major parts:
• Glucose activation
• Energy harvest
Copyright © 2009 Pearson Education Inc.
7.3 What Happens During Glycolysis?
 Glucose activation
• The activation of glucose uses up some ATP
energy.
• Two ATP molecules are used to
phosphorylate glucose to form fructose
bisphosphate.
2 ATP
C C C C C C
glucose
2 ADP
C C C C C C
P
fructose P
bisphosphate
1 Glucose activation
Copyright © 2009 Pearson Education Inc.
Fig. 7-2-1
7.3 What Happens During Glycolysis?
 Energy harvest from glycolysis
• Two molecules of fructose bisphosphate split
into two glyceraldehyde-3-phosphate (G3P)
molecules.
• Each G3P molecule is converted to pyruvate.
4 ADP
4
ATP
2 C C C
G3P
P
2 C C C
pyruvate
2 NAD+
2 NADH
2 Energy harvest
Copyright © 2009 Pearson Education Inc.
Fig. 7-2-2
7.3 What Happens During Glycolysis?
 The essentials of glycolysis
2 ATP
C C C C C C
4 ADP
2 ADP
C C C C C C
glucose
P
1 Glucose activation
fructose P
bisphosphate
4
ATP
2 C C C
G3P
P
2 C C C
pyruvate
2 NAD+
2 NADH
2 Energy harvest
• Two ATPs are used to activate glucose.
• Two ATPs are made for each pyruvate (four total).
• Each conversion to pyruvate forms one molecule of NADH (two
total).
• Net gain from glycolysis: 2ATP + 2 NADH
Copyright © 2009 Pearson Education Inc.
7.4 What Happens During Cellular
Respiration?
 Cellular respiration is the second stage of glucose
metabolism, and it occurs only in the presence of
oxygen.
 Cellular respiration occurs in the mitochondria.
 Large amounts of ATP are produced by this process,
which converts pyruvate to CO2 and H2O.
Copyright © 2009 Pearson Education Inc.
intermembrane
compartment
mitochondrion
inner
membrane
outer
membrane
matrix
glucose
cristae
Glycolysis
1
coenzyme A
2 pyruvate
2
ATP
ATP-synthesizing
enzyme
electron
transport
chain
outer
membrane
intermembrane
compartment
inner
membrane
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6
H+
H+
ADP
ATP
5
H+
H+
H+
acetyl CoA
CO2
7
H+
(cytoplasmic
fluid)
ATP
H+
8
4
H+
2e–
1/2 O2
2e–
2 H+
3
H2O
Krebs
cycle
(matrix)
energized
electron
carriers:
NADH, FADH2
CO2
depleted carriers: NAD+, FAD
Fig. 7-3
7.4 What Happens During Cellular
Respiration?
Steps of cellular respiration:
• Step 1: Two molecules of pyruvate produced by glycolysis are
transported into the matrix of a mitochondrion.
• Step 2: Each pyruvate is split into CO2 and acetyl CoA, which
enters the Krebs cycle.
• The Krebs cycle produces one ATP from each pyruvate, and
donates electrons to NADH and flavin adenine dinucleotide
(FADH2).
Copyright © 2009 Pearson Education Inc.
7.4 What Happens During Cellular
Respiration?
• Step 3: NADH and FADH2 donate energized electrons to
the electron transport chain of the inner membrane.
• Step 4: In the electron transport chain, electron energy is
used to transport hydrogen ions (H+) from the matrix to the
intermembrane compartment.
• Step 5: Electrons combine with O2 and H+ to form H2O.
Copyright © 2009 Pearson Education Inc.
7.4 What Happens During Cellular
Respiration?
• Step 6: Hydrogen ions in the intermembrane compartment
diffuse across the inner membrane, down their
concentration gradient.
• Step 7: The flow of ions into the matrix provides the
energy to produce ATP from ADP.
• Step 8: ATP moves out of mitochondrion into the
cytoplasm.
Copyright © 2009 Pearson Education Inc.
7.4 What Happens During Cellular
Respiration?
 The Krebs cycle breaks down pyruvate in the
mitochondrial matrix.
• Pyruvate produced by glycolysis reaches the matrix and
reacts with coenzyme A, forming acetyl CoA.
• During this reaction, two electrons and a H+ are transferred
to NAD+ to form NADH.
• Acetyl CoA enters the Krebs cycle and produces one ATP,
one FADH2, and three NADH.
Copyright © 2009 Pearson Education Inc.
7.4 What Happens During Cellular
Respiration?
 The reactions in the mitochondrial matrix
1 Formation of
acetyl CoA
coenzyme A
3 NADH
3 NAD+
C CO2
NAD+
FADH2
coenzyme A
C C CoA
acetyl CoA
C C C
pyruvate
FAD
2 Krebs
cycle
NADH
2 C CO2
ADP
ATP
Copyright © 2009 Pearson Education Inc.
Fig. 7-4
7.4 What Happens During Cellular
Respiration?
 Energetic electrons are carried to the electron transport
chain.
• Step 1: Energized carriers deposit their electrons in the
electron transport chains (ETC) in the inner mitochondrial
membrane.
• Step 2: Electrons in the ETC move from one molecule to the
next, transferring energy that is used to pump H+ out of the
matrix and into the intermembrane compartment.
• Step 3: At the end of the ETC, oxygen atoms combine with
two H+ and two depleted electrons to form H2O.
Copyright © 2009 Pearson Education Inc.
7.4 What Happens During Cellular
Respiration?
• Oxygen accepts electrons after they have
passed through the ETC and given up most of
their energy.
• If O2 is not present, electrons accumulate in
the ETC, H+ pumping out of the matrix stops,
and cellular respiration ceases.
Copyright © 2009 Pearson Education Inc.
7.4 What Happens During Cellular
Respiration?
 The electron transport chain in the
mitochondrial matrix
(matrix)
3
FADH2
NADH
2e–
NAD+
1/2 O2 + 2H+
FAD
2e–
H2O
1
electron
carriers
(inner
membrane)
H+
2
energy to drive
H+
ATP
H+
synthesis
(intermembrane compartment)
Copyright © 2009 Pearson Education Inc.
Fig. 7-5
7.4 What Happens During Cellular
Respiration?
 Energy from a hydrogen-ion gradient is used to
produce ATP.
• Hydrogen ions accumulate in the intermembrane
compartment and diffuse back into the matrix.
• The energy released when hydrogen ions move down
their concentration gradient is used to make ATP in a
process called chemiosmosis.
• During chemiosmosis, 32 to 34 molecules of ATP are
produced from each molecule of glucose.
• This ATP is transported from the matrix to the cytoplasm,
where it is used to power metabolic reactions.
Copyright © 2009 Pearson Education Inc.
7.5 What Happens During Fermentation?
 When oxygen is not present (anaerobic conditions),
glucose cannot be metabolized by cellular respiration;
instead, fermentation takes place.
 Unlike cellular respiration, fermentation generates no ATP,
but instead, regenerates NAD+ that is used to get ATP
from glycolysis.
 pyruvate acts as an electron acceptor from the NADH produced
during glycolysis.
 When pyruvate accepts electrons from NADH, it recycles the NAD+
so that more glucose can be converted to pyruvate, generating a
small amount of ATP in the process.
 When no O2 is present, glycolysis becomes the main source of ATP
and NADH production.
Copyright © 2009 Pearson Education Inc.
7.5 What Happens During Fermentation?
 There are two types of fermentation: one converts
pyruvate to ethanol and CO2, and the other converts
pyruvate to lactate.
• Alcoholic fermentation is the primary mode of
metabolism in many microorganisms.
• The reactions use hydrogen ions and electrons from NADH,
thereby regenerating NAD+.
• Alcoholic fermentation is responsible for the production of
many economic products, such as wine, beer, and bread.
Copyright © 2009 Pearson Education Inc.
7.5 What Happens During Fermentation?
 Glycolysis followed by alcoholic fermentation
NAD+
NADH
NADH
NAD+
2 C C C
2 C C +2 C
C C C C C C
(glycolysis)
(fermentation)
glucose
pyruvate
ethanol CO2
2 ADP
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2 ATP
Fig. 7-6
7.5 What Happens During Fermentation?
 Other cells ferment pyruvate to lactate, and include
microorganisms that produce yogurt, sour cream, and cheese.
 Lactate fermentation also occurs in aerobic organisms
when cells are temporarily deprived of oxygen, such as
muscle cells during vigorous exercise.
 These muscle cells ferment pyruvate to lactate, which uses H+
and electrons from NADH to regenerate NAD+.
Copyright © 2009 Pearson Education Inc.
7.5 What Happens During Fermentation?
 Glycolysis followed by lactate fermentation
NAD+
NADH
NADH
NAD+
2 C C C
2 C C C
C C C C C C
(glycolysis)
(fermentation)
glucose
pyruvate
lactate
2
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ADP
2
ATP
Fig. 7-8