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Harvesting
Energy:
Glycolysis and
Cellular
Respiration
Chapter 8
Using the Energy from
Photosynthesis
6CO2 + 6H2O + light
• Some ATP is produced in photosynthesis,
but most energy is stored in sugars.
• In the mitochondria of eukaryotic cells,
glucose is broken down into CO2,
releasing energy as ATP.
C6H12O6 + 6O2
Energy Produced through the
Breakdown of Glucose
C6H12O6 + 6O2 + heat
6CO2 + 6H2O + ATP + heat
Energy Carrier Molecules
• Energy released from ATP
• Three major metabolic stages that
produce energy from glucose:
– Glycolysis
– Krebs Cycle
– Electron Transport Chain (ETC)
+
+
• H+ and electrons released from NADH
NAD
H
NAD
+
H
+ 2e-
Glycolysis
Glycolysis
• “To Break Apart a Sweet”
• Glucose must be activated by addition of
phosphate to harvest energy.
• Net energy harvest = 2 ATP and 2 NADH
Energy Generation through
Respiration
Glucose
Within the
cytosol
1
2
3
Fermentation
• Only occurs under certain circumstances:
– If no mitochondria are present.
– If no O2 is available, anaerobic conditions.
Glycolysis
Pyruvate
1. Glucose is activated,
using two ATP, by the
addition of phosphate
creating fructose
bisphosphate.
2. Fructose bisphosphate
is split into two
glyceraldehyde 3phosphate molecules.
3. G3P transfers
phosphates to ADP,
generating ATP and
pyruvate.
• Regenerates NAD+ for glycolysis.
• Two types of fermentation:
Within
mitochondria
Fermentation
Krebs Cycle
No ATP production
32-34 ATP produced
– Lactic Acid Fermentation
– Alcohol Fermentation
Alcohol
Fermentation
Alcohol Fermentation
• Oxygen is not needed in fermentation (anaerobic).
– Many microorganisms use glycolysis to make ATP and
fermentation to regenerate NAD+
– Yeast switches to alcoholic fermentation if O2 is not
available
• Wine and beer
• Bread holes
• Sour cream, yogurt, cheese
Lactic Acid
Fermentation
• Oxygen is not needed in
fermentation (anaerobic).
– Our muscle cells switch to lactic
acid fermentation to generate ATP
when O2 is scarce.
– Lactate can cause muscle fatigue
and pain.
– Ultimately lactic acid converted
back to pyruvate in the liver.
Lactic Acid Fermentation
Energy Generation through
Respiration
Glucose
Mitochondria
Glycolysis
Glucose
Pyruvate
Glycolysis
Pyruvate
Within the
cytosol
Krebs
Cycle
Within
mitochondria
Fermentation
Krebs Cycle
No ATP production
32-34 ATP produced
Mitochondria
• “The Powerhouse of the Cell”
• Possesses two
membrane creating
compartments.
• Respiration occurs
within its
membrane.
Electron
Transport
Chain
Additional Energy Generation
• Extracting further energy from glucose occurs in
two steps.
– First, pyruvate is
converted into acetylCoA (coenzyme A),
releasing CO2.
– Net Energy Harvest =
1 NADH
Krebs
Cycle
• Second, energy is
generated through
the Krebs cycle, or
citric acid cycle.
• An additional energy carrier molecule, FAD is
utilized.
• Net Energy Harvest = 1 ATP, 3 NADH, and 1 FADH2.
Glucose Metabolism
Krebs Cycle
1
1. Pyruvate from glycolysis is
converted to acetyl-CoA,
generating one NADH.
2
2. Coenzyme A is recycled
producing citrate.
3. Citrate is converted to
succinate, then to oxaloacetate
before returning to citrate with
utilizing CoA, generating three
NADH, one ATP, and one
FADH2.
3
Glucose Metabolism and
Respiration
Glycolysis:
Glucose
2 pyruvate + 2 NADH + 2 ATP
Formation of acetyl-CoA:
1 NADH per pyruvate
(2 NADH per glucose)
Krebs Cycle:
3 NADH + 1 FADH2 + 1 ATP per pyruvate
(6 NADH + 2 FADH2 + 2 ATP per glucose)
Total:
10 NADH + 2 FADH2 + 4 ATP per glucose
Electron Transport Chain of Mitochondria
•The cell produces only 4 ATP molecules during
glycolysis and the Krebs cycle.
•Additional high-energy electron carriers have been
made (10 NADH and 2 FADH2).
•Along the inner membrane of the mitochondria,
electrons
from NADH
and FADH2
are used to
generate
more ATP.
Electrons power
H+ transport across
the membrane
Electrons are fed
into the electron
transport chain.
Oxygen accepts
spent electrons,
making water.
A high concentration
gradient of H+ is
generated.
Mechanism of ATP Synthesis
Membrane
ATP Synthase,
from the RCSB Protein Databank
http://pdbbeta.rcsb.org
Flow of H+ back
across the membrane
is coupled to ATP
synthesis.
Mechanism of ATP Synthesis
Start Movie
Summary
Efficiency of Respiration
1. Glucose is converted
into pyruvate.
2. In the absence of O2,
fermentation of
pyruvate occurs.
3. In the presence of O2,
pyruvate is brought
into the mitochondria
for cellular respiration.
4. Electrons are stripped
from C-molecules and
fed to the ETC to
generate ATP.
• Cellular Respiration
– 40% efficiency
– ~ 60% is lost as heat
• Most efficient cars
– ~25% of energy stored in gasoline to energy
that moves car.
– ~75% lost as heat.
Other organic
molecules feed
into glycolysis
and the Krebs
cycle.
Process
Location
e- Carrier ATP per
Formed Glucose
Glycolysis
Cytosol
2 NADH
2 ATP
Cellular
Respiration
Mitochondrial
Matrix
2 NADH
none
Mitochondrial 6 NADH,
Matrix
2 FADH2
Electron
Mitochondrial
none
Transport Chain
Membrane
Krebs Cycle
2 ATP
28-30
ATP
Homework
Chapter 8
Thinking Through the Concepts,
Review Question 7