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Glycolysis and Fermentation
Chemical Energy & Food
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We get energy from the
food we eat
One gram of glucose
(C6H12O6) releases 3811
calories of heat energy
Calorie – the amount of
energy needed to raise the
temperature of 1 gram of
water 1 degree Celsius
 The Calorie on food labels
represents 1 kilocalorie (1,000
calories)
Overview of Cell
Respiration
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Cellular respiration is the process that releases
energy by breaking down glucose and other food
molecules in the presence of oxygen
6O2 + C6H12O6
6CO2 + 6H2O + 36ATP
Oxygen + glucose = carbon dioxide + water +
energy
When oxygen is available, cell respiration
happens in 3 steps:
1. Glycolysis (occurs in the cytoplasm)
2. Krebs cycle (occurs in the mitochondria)
3. Electron transport chain (occurs in the mitochondria)
Glycolysis
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Glycolysis is the process in which one
molecule of glucose is broken in half,
producing two molecules of pyruvic acid
Pyruvic acid is a 3-carbon compound
Glycolysis needs 2 ATP to get started
Glycolysis produces 4 ATP
The net gain in ATP by glycolysis is…
Glycolysis also adds 2 high-energy
electrons to the electron carrier NAD+
 NAD+ become NADH when it is carrying a pair of
high-energy electrons
Fermentation
Fermentation occurs
after glycolysis when
oxygen is not present
 Fermentation releases
energy from food
molecules by producing
ATP in the absence of
oxygen
 Fermentation is
anaerobic because it
does not require oxygen
 2 Types
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 Alcoholic fermentation
 Lactic acid fermentation
Alcoholic Fermentation
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Yeast and a few other microorganisms use
alcoholic fermentation
Ethyl alcohol and carbon dioxide are formed as
wastes
Lactic Acid Fermentation
Pyruvic acid is converted to
lactic acid and NAD+ is
regenerated
 Lactic acid is produced in
your muscles during rapid
exercise when the body
cannot supply enough
oxygen to the tissues
 Lactic acid buildup causes
pain in muscles
 Lactic acid fermentation by
prokaryotes is used to
produce foods like cheese,
yogurt, and sour cream
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Krebs Cycle and Electron Transport
Aerobic Respiration
Aerobic respiration
requires oxygen in
order to occur
 The energy-releasing
pathways in cells
require oxygen, which
is why we breathe, or
respire
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Krebs Cycle
In the presence of oxygen, the Krebs
cycle follows glycolysis
 The Krebs cycle occurs in the
mitochondria
 During the Krebs cycle, pyruvic acid is
broken down into carbon dioxide and
energy
 At the end of the Krebs cycle, 2 ATP are
produced and high-energy electrons are
added to the electron carriers NAD+ and
FAD, forming NADH and FADH2
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Electron Transport Chain
NADH and FADH2 carry high-energy
electrons from the Krebs cycle to the
electron transport chain (ETC)
 The ETC uses high-energy electrons from
the Krebs cycle to convert ADP to ATP
 The protein ATP synthase is at the end of
the ETC and produces 32 ATP
 Water is also produced as a waste product
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Total Energy Produced
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Glycolysis produces a net
of 2 ATP
The Krebs cycle produces
2 ATP
The electron transport
chain produces 32 ATP
One glucose molecule
produces a net of 36 ATP
This is 18 times the
amount that is produced
without oxygen
Energy & Exercise
You only have
enough ATP
produced by
glycolysis in your
cells for a few
seconds of vigorous
activity
 After that, your
muscle cells produce
more ATP through
lactic acid
fermentation
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 This will give you
about another 90
sec. of energy
Energy & Exercise
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You need O2 to get rid of the lactic acid build-up
 This lack of O2 is called an Oxygen Debt
 This is why you breathe heavy after you run!
After about 90 sec. your body uses cellular
respiration with glycogen (for about 15-20 min)
 Next, your body starts breaking down fats
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oxygen
carbon
dioxide
water
Comparing Photosynthesis &
Cellular Respiration