2. Chapter 8 2
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
4. Chapter 8 4
Overview of Glucose Breakdown
Glycolysis
• Occurs in the cytosol
• Does not require oxygen
• Breaks glucose into pyruvate
• Yields two molecules of ATP per molecule
of glucose
5. Chapter 8 5
Overview of Glucose Breakdown
If oxygen is absent fermentation occurs
• pyruvate is converted into either lactate, or
into ethanol and CO2
If oxygen is present cellular respiration
occurs…
6. Chapter 8 6
Overview of Glucose Breakdown
Cellular respiration
• Occurs in mitochondria (in eukaryotes)
• Requires oxygen
• Breaks down pyruvate into carbon dioxide
and water
• Produces an additional 32 or 34 ATP
molecules, depending on the cell type
7. Chapter 8 7
Glycolysis
Overview of the two major phases of
glycolysis
• Glucose activation phase
• Energy harvesting phase
8. Chapter 8 8
Glycolysis
Glucose activation phase
• Glucose molecule converted to highly
reactive fructose bisphosphate by two
enzyme-catalyzed reactions, using 2
ATPs
9. Chapter 8 9
Essentials of Glycolysis (a)
Glucose-6-
ATP ADP
P Phosphate
Glucose
CCCCCC CCCCCC
Glucose-6- Fructose-1,6-
P P
Phosphate Bisphosphate
CCCCCC CCCCCC
P
ATP ADP
10. Chapter 8 10
Glycolysis
Energy harvesting phase
• Fructose bisphosphate is split into two
three-carbon molecules of glyceraldehyde
3-phosphate (G3P)
• In a series of reactions, each G3P
molecule is converted into a pyruvate,
generating two ATPs per conversion, for
a total of four ATPs
• Because two ATPs were used to activate
the glucose molecule there is a net gain
of two ATPs per glucose molecule
11. Chapter 8 11
Essentials of Glycolysis (b)
Fructose-1,6-
P Bisphosphate
CCCCCC
P
P
CCC
CCC
P
CCC CCC
G3P
P P
12. Chapter 8 12
Glycolysis
Energy harvesting phase (continued)
• As each G3P is converted to pyruvate,
two high-energy electrons and a
hydrogen ion are added to an “empty”
electron-carrier NAD+ to make the high-
energy electron-carrier molecule NADH
• Because two G3P molecules are
produced per glucose molecule, two
NADH carrier molecules are formed
13. Chapter 8 13
Essentials of Glycolysis (c)
CCC CCC
G3P
Pi Pi
P P
NAD+ NAD+
NADH NADH
CCC CCC
P
P P P
ADP ADP
ADP ADP
ATP ATP
ATP ATP
C C C Pyruvates C C C
14. Chapter 8 14
Glycolysis
Summary of glycolysis:
• Each molecule of glucose is broken down
to two molecules of pyruvate
• A net of two ATP molecules and two
NADH (high-energy electron carriers) are
formed
16. Chapter 8 16
Fermentation
Pyruvate is processed differently under
aerobic and anaerobic conditions
Under aerobic conditions, the high
energy electrons in NADH produced in
glycolysis are ferried to ATP-
generating reactions in the
mitochondria, making NAD+ available
to recycle in glycolysis
17. Chapter 8 17
Fermentation
Under anaerobic conditions, pyruvate is
converted into lactate or ethanol, a
process called fermentation
Fermentation does not produce more
ATP, but is necessary to regenerate
the high-energy electron carrier
molecule NAD+, which must be
available for glycolysis to continue
18. Chapter 8 18
Fermentation
Some microbes ferment pyruvate to other
acids (as seen in making of cheese,
yogurt, sour cream)
Some microbes perform fermentation
exclusively (instead of aerobic
respiration)
Yeast cells perform alcoholic fermentation
19. Chapter 8 19
Alcoholic Fermentation
O
C O
O C
O
NAD
NAD NADH NADH +
+
NAD+
NAD+ NADH NADH
CCC CC
Alcoholic
Glycolysis
CCCCCC
Fermentation C C
Glucoses CCC
Pyruvates Ethanols
ADP ATP
ADP ATP
20. Chapter 8 20
Fermentation
Some cells ferment pyruvate to form
acids
Human muscle cells can perform
fermentation
• Anaerobic conditions produced when
muscles use up O2 faster than it can be
delivered (e.g. while sprinting)
• Lactate (lactic acid) produced from
pyruvate
21. Chapter 8 21
Lactate Fermentation
NAD+ NADH NADH NAD+
NAD+ NADH NADH NAD+
CCC CCC
Lactate
Glycolysis
CCCCCC
Fermentation C C C
Glucoses CCC
Pyruvates Lactates
ADP ATP
ADP ATP
22. Chapter 8 22
Cellular Respiration
In eukaryotic cells, cellular respiration occurs
within mitochondria, organelles with two
membranes that produce two
compartments
• The inner membrane encloses a central
compartment containing the fluid matrix
• The outer membrane surrounds the
organelle, producing an intermembrane
space
23. Chapter 8 23
A Mitochondrion One of Its
Mitochondria
a
b
A Cell
A Crista
Outer
& Inner
Membranes c
Intermembrane Matrix
Compartment
24. Chapter 8 24
Cellular Respiration
Overview of Aerobic Cellular
Respiration:
Glucose is first broken down into
pyruvate, through glycolysis, in the
cell cytoplasm
Pyruvate is transported into the
mitochondrion (eukaryotes) and split
into CO2 and a 2 carbon acetyl group
25. Chapter 8 25
Cellular Respiration
The acetyl group is further broken down
into CO2 in the Krebs Cycle (matrix
space) as electron carriers are loaded
Electron carriers loaded up in glycolysis
and the Krebs Cycle give up
electrons to the electron transport
chain (ETC) along the inner
mitochondrial membrane
26. Chapter 8 26
Cellular Respiration
A hydrogen ion gradient produced by the
ETC is used to make ATP
(chemiosmosis)
ATP is transported out of the
mitochondrion to provide energy for
cellular activities
28. Chapter 8 28
Pyruvate Breakdown in Mitochondria
After glycolysis, pyruvate diffuses into
the mitochondrion into the matrix
space
Pyruvate is split into CO2 and a 2-carbon
acetyl group, generating 1 NADH per
pyruvate
29. Chapter 8 29
Pyruvate Breakdown in Mitochondria
Acetyl group is carried by a helper
molecule called Coenzyme A, now
called Acetyl CoA
Acetyl CoA enters the Krebs Cycle and is
broken down into CO2
30. Chapter 8 30
Pyruvate Breakdown in Mitochondria
Electron carriers NAD+ and FAD are
loaded with electrons to produce 3
NADH & 1 FADH2 per Acetyl CoA
6. One ATP also made per Acetyl CoA
in the Krebs Cycle
31. Chapter 8 31
Formation of Acetyl CoA
O O
C C
CCC Pyruvates C C C
O O
NAD+ NAD+
NADH NADH
CCC CCC
CoA CoA
CoA CoA
C C Acetyl CoA C C
32. Chapter 8 32
Krebs Cycle: Summary
CoA CoA
CoA CoA
C C Acetyl CoA C C
1
C C
CCCCC CCCCC
O O
CCCC CCCC
C C
NAD NAD
+ +
O O
NADH NADH
2 3
NADH
NADH C
CCCCC CCCCC
NAD+
NAD+
H2O H2O 567
NAD+ NAD+
FADH2
O O
FADH2
NADH NADH
C C
FAD
O O
FAD
ADP ADP
ATP ATP
4
CCCC CCCCC
H 2O H 2O
33. Chapter 8 33
Electron Transport Chain
Most of the energy in glucose is stored
in electron carriers NADH and FADH2
• Only 4 total ATP produced per glucose
after complete breakdown in the Krebs
Cycle
34. Chapter 8 34
Electron Transport Chain
NADH and FADH2 deposit electrons into
electron transport chains in the inner
mitochondrial membrane
Electrons join with oxygen gas and
hydrogen ions to made H2O at the end
of the ETCs
36. Chapter 8 36
Chemiosmosis
Energy is released from electrons as they
are passed down the electron
transport chain
Released energy used to pump hydrogen
ions across the inner membrane
• Hydrogen ions accumulate in
intermembrane space
37. Chapter 8 37
Chemiosmosis
Hydrogen ions form a concentration
gradient across the membrane, a form
of stored energy
Hydrogen ions flow back into the matrix
through an ATP synthesizing enzyme
• Process is called chemiosmosis
38. Chapter 8 38
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
42. Chapter 8 42
Influence on How Organisms Function
Metabolic processes in cells are heavily
dependent on ATP generation (cyanide
kills by preventing this)
Muscle cells switch between fermentation
and aerobic cell respiration depending
on O2 availability
44. Chapter 8 44
Energy Harvested from Glucose
Glucose
(Cytoplasm)
4 ATP
Glycolysis
2 ATP
2 Pyruvates
2 NADH
(Mitochondrial 2 CO2
2 NADH
Matrix)
Krebs 4 CO2
6 NADH
Cycle
2 FADH2
2 ATP
(Inner
Membrane) Water
Electron Transport
System
Oxygen 32 ATP