Chemical Pathways
Cellular Respiration (aerobic) – process that releases
energy by breaking down glucose and other food
molecules; O2 is required
6O2 + C6H12O6  6CO2 + 6H2O + ATP
3 Major sets of reactions – glycolysis, Krebs Cycle,
electron transport chain
 Fermentation (anaerobic) – process that releases
energy from food without O2 – Fig. 9-4
2 Major sets of reactions – glycolysis, fermentation
 NADH – an electron carrier molecule

Glycolysis – breakdown of glucose to
produce: 2 pyruvic acid, 2 NADH,
**net gain of 2 ATP

http://www.youtube.com/watch?v=3GTjQTq
UuOw
Fermentation – conversion of pyruvic
acid to some end product
** no ATP produced
Lactic acid fermenation – end product is
lactic acid (ex. Animal cells, lactic
acid bacteria)
Alcoholic fermentation – end products
are ethanol & CO2 (ex. Bacteria &
yeast)
**For each molecule of glucose only 2
ATP are produced during anaerobic
respiration.**
Glycolysis – exact same steps as in
anerobic respiration; takes place in
the cytoplasm;
At the end of glycolysis
approximately 90% of the energy is
still stored in pyruvic acid
molecules
These two pyruvic acid molecules
will enter the Krebs Cycle (citric
acid cycle)
Glycolysis
Krebs cycle (citric acid cycle) – the two
pyruvic acids molecules that are
products of glycolysis are broken
down in a series of energyextracting reactions
Takes place in the matrix of the
mitochondria
Krebs cycle (con’t)
1. Citric Acid Production – pyruvic
acid is completely oxidized to
produce:
a. 2 NADH
b. 2 CO2
c. 2 Citric Acid molecules
Krebs cycle (con’t)
2. Energy extraction – series of
chemical reactions (cycle) to
produce (for each pyruvic acid)
a. 1 ATP
b. 3 NADH
c. 2 FAD
d. 2 CO2
http://www.youtube.com/watch?v=KAjUsiZWywk&feature
=related
Electron Transport Chain – uses the
high energy electrons from
glycolysis and the Krebs cycle to
synthesize ATP from ADP and Pi
MOST of the energy produced from the
breakdown of glucose occurs here
(32/34 ATP molecules)
O2 is the final electron acceptor
***For each molecule of glucose, 36/38
ATP are produced during aerobic
respiration***
***Much more energy efficient than
anaerobic respiration****
Fats and proteins are broken down at
various points along respiratory
pathway
Proteins produce about the same
amount of ATP as glucose
Fats produce about twice as much
energy as glucose
The body uses ATP from 3 basic
sources; ATP stored in muscle cells,
and ATP produced by aerobic &
anaerobic respiration
The ATP stored in muscle cells only
lasts for the first few seconds of
activity.
ATP produced by anaerobic respiration
is used up in about 90 seconds.
Oxygen debt is the amount of O2
required to convert lactic acid to
glucose.
Aerobic respiration produces the ATP
to sustain activities that go on
longer. That is why athletes must
pace themselves.