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Harvesting Chemical Energy
• ATP--main fuel for cells
• Cellular Respiration--process cells use to
make ATP by breaking down organic
compounds
Glucose
Glycolysis
Krebs
cycle
Fermentation (without
oxygen)
Electron
transport
Alcohol or
lactic acid
Mitochondrion
Electrons carried in NADH
Pyruvic
acid
Glucose
Glycolysis
Krebs
Cycle
Electrons
carried in
NADH and
FADH2
Electron
Transport
Chain
Mitochondrion
Cytoplasm
The Cell Respiration Equation
• 6O2 + C6H12O6
6CO2 + 6H2O + Energy
• oxygen + sugar carbon dioxide + water + energy
Glucose
2 Pyruvic acid
Glycolysis
• The process of breaking 1 molecule of
glucose in half
• Happens in the cytoplasm
• Produces pyruvic acid and NADH
• Produces 4 ATPs overall
• 2 ATPs used up to in the reaction
• Net gain = 2 ATPs
NAD+ and NADH
• NAD+ is a carrier molecule, it becomes
NADH when it picks up energy (an
electron)
• It is similar to NADPH, used in
photosynthesis
• Carries high energy electrons to other places
they are needed in the cell
Glycolysis
• This is a FAST process
• Thousands of ATPs can be produced in a
few milliseconds
• However, there are a limited number of
NAD+ carriers, so more must be made
• Without additional NAD+, glycolysis
cannot continue
Glucose
Glycolysis
Krebs
cycle
Fermentation (without
oxygen)
Electron
transport
Alcohol or
lactic acid
• The next step of cell respiration depends on
whether or not oxygen is available
• If no oxygen, then the next step is called
FERMENTATION
• Fermentation is an anaerobic process
• Two types of fermentation--alcoholic
fermentation and lactic acid fermentation
Alcoholic Fermentation
• Yeasts and a few other microorganisms use this
• pyruvic acid + NADH --> alcohol + CO2 + NAD+
• Used to produce bread,
• wine, beer,
homeade rootbeer, etc.
The “holes” in bread are from
pockets of CO2 that got trapped.
Lactic Acid Fermentation
• This type of fermentation happens in your
muscles, and also in certain microorganisms
• pyruvic acid + NADH --> lactic acid + NAD+
Used to produce cheese, yogurt, soy
sauce, sauerkraut, etc. Lactic acid
gives these things the sharp, sour
taste. YUMMMMY!
Lactic Acid Fermentation
• This is also the reason for runner’s
fatigue or cramps
• When exercising strenously, your
muscle cells use up all your
oxygen and must switch to lactic
acid fermentation
• Lactic acid burns when it builds
up inside the cells
Lactic Acid Fermentation
• Since NAD+ is produced…
• pyruvic acid + NADH -->
lactic acid + NAD+
• …glycolysis can continue and
more ATP can be made
Glucose
(C6H1206)
+
Oxygen
(02)
Glycolysis
Krebs
Cycle
Electron
Transport
Chain
Carbon
Dioxide
(CO2)
+
Water
(H2O)
After Glycolysis...
• Most of the energy in glucose is still not
released even after glycolysis
• Oxygen is needed to release the remaining
energy from the glucose molecule
• The next step is called the Krebs Cycle (if
oxygen is available)
Mitochondrion
Krebs Cycle
• What goes IN? pyruvic acid from glycolysis
• Where? Mitochondrial matrix (space inside
the inner membrane of mitochondria)
• What comes OUT? NADH and FADH2
(both are carrier molecules for high energy
electrons). These go to the
next step of cellular
respiration...
Krebs Cycle
• When pyruvic acid enters mitochondria, it
reacts with coenzyme A to make acetyl CoA
& releases
CO2
christae
Krebs Cycle
• 5 Major Steps
– 1) combines with oxalocetic acid to form citric
acid
– 2) releases CO2 and NAD+ to NADH
– 3) CO2 released and NAD to NADH, also ATP
synthesized
– 4) FAD (carrier molecule) to FADH2
– 5) NAD+ to NADH, more oxalocetic acid
created
5 Major Steps
1) combines with
oxalocetic acid to form
citric acid
2) releases
CO2 and
Mitochondrion
NAD+ to NADH
3) CO2 released and
NAD to NADH, also ATP
synthesized
4) FAD (carrier
molecule) to FADH2
5) NAD+ to NADH, more
oxalocetic acid created
Electron Transport
Hydrogen Ion Movement
Channel
Mitochondrion
Intermembrane
Space
ATP synthase
Inner
Membrane
Matrix
ATP Production
Electron Transport Chain
• What goes IN? NADH and FADH2 from
Krebs Cycle
• Where? Inner membrane of mitochondria
• What comes OUT? Lots and lots of ATP
molecules!!!! (34 to be exact)
Electron Transport
Hydrogen Ion Movement
Channel
Mitochondrion
Intermembrane
Space
ATP synthase
Inner
Membrane
Matrix
ATP Production
Electron Transport Chain
• High energy electrons are passed from
NADH and FADH2 along a series of
molecules
• As they go from molecule to molecule, they
lose their energy. It is used to pump H+
into the space between inner and outer
mitochondrial membrane.
Electron Transport Chain
• Chemiosmosis takes place, H+ ions diffuse
from high to low through ATP synthase
• As the ATP synthase spins, this generates
ATP molecules
• Sound familiar?
Electron Transport Chain
• Oxygen is the final electron acceptor in this
reaction
• This gets rid of low energy electrons and
extra H+ ions
• Byproduct that results is H2O
The Totals (Net Gains)
• Glycolysis + Fermentation = 2 ATP
• Glycolysis + Krebs + ETC = 36 ATP
• Even 36 ATP is only about 66% of the
energy available in one glucose molecule.
Where does the rest of the energy go???
• The remaining 34% is given off as body
heat (keeps you warm in this chilly room!)
Pacing Yourself
• Fermentation--used
during strenuous
exercise (fast
breakdown of sugar)
• Krebs Cycle and ETC-used during longer,
paced exercises (like
long-distance running)
Slower, but more
energy released
Why do runners breathe heavily
after a race?
They are “repaying” the
oxygen debt they have built
up!
• Photosynthesis--removes CO2 from the
atmosphere, puts back O2
6H2O + 6CO2 + light energy C6H12O6 + 6O2
• Cellular Respiration--removes O2 from the
atmosphere, puts back CO2
6O2 + C6H12O6  6CO2 + 6H2O + Energy