Download 4.6 Fermentation

Fermentation
Chapter 4: Cells and Energy
Section 6: Fermentation
Aerobic vs. Anaerobic
• Cellular respiration is aerobic respiration
– Two of the three phases of cellular respiration
require oxygen
• Which phase does NOT require oxygen?
• The body cannot store large amounts of O2
– The amount of oxygen provided by breathing is
enough to sustain cellular respiration during
normal activities
Aerobic vs. Anaerobic
• But what happens when you are doing high
levels of activity?
– There is not enough oxygen to sustain cellular
respiration despite breathing faster.
How do cells make energy without oxygen?
Aerobic vs. Anaerobic
In the absence of oxygen, the cell will begin
anaerobic respiration in order to produce
chemical energy.
• Recall: Glycolysis is an anaerobic process
– Glycolysis is the breakdown of glucose
– Glycolysis produces 2 pyruvates, 2 ATP and 2
NADH
Fermentation
• The production of ATP continues in anaerobic
respiration through glycolysis and
fermentation.
• Fermentation- the process in which electrons
are removed from NADH to create NAD+
molecules
– Does not make ATP
– Instead, the purpose of fermentation is to allow
glycolysis to continue
Glycolysis and Fermentation
Why does glycolysis need fermentation in order
to continue?
• Glycolysis needs an electron carrier molecule
– Without NAD+, glycolysis would stop
– By picking up high, energy electrons, a eukaryotic
cell can continue to break down glucose for a
small amount of ATP
Fermentation
There are two types of fermentation:
1. Lactic Acid Fermentation
2. Alcoholic Fermentation
Lactic Acid Fermentation
• Lactic Acid Fermentation
– Occurs in muscle cells, cells of other vertebrates
and some microorganisms
– Lactic acid (C3H6O3)
• Causes your muscles to “burn” during hard exercise
Lactic Acid Fermentation
Steps of Lactic Acid Fermentation:
1. Pyruvate and NADH from glycolysis enter the
fermentation process. Two NADH molecules
provide energy to convert pyruvate into lactic
acid.
2. Two molecules of NAD+ are recycled back to
glycolysis
Lactic Acid Fermentation
Lactic Acid Fermentation
• By itself, fermentation does not produce ATP
– Instead, it removes H+ and electrons from NADH
– The NAD+ is then able to be returned to glycolysis,
where 2 ATP are made
• During lactic acid fermentation, lactic acid
builds up in muscle cells
– When O2 becomes available, cellular respiration
begins again, quickly breaking down lactic acid
• This is why you breathe hard for several minutes for
several minutes after you stop exercising
Alcoholic Fermentation
• Alcoholic Fermentation
– Occurs in many yeasts and some types of plants
Alcoholic Fermentation
Steps of Alcoholic Fermentation:
1. Pyruvate and NADH from glycolysis enter the
fermentation process. Two NADH molecules
provide the energy needed to break pyruvate
into an alcohol and CO2
2. Two molecules of NAD+ are recycled back to
glycolysis
Alcoholic Fermentation
Alcoholic Fermentation
• Often the alcohol produced is ethyl alcohol
Alcoholic Fermentation
Example of Alcoholic Fermentation:
• Yeast is used to cause bread to rise
– Sugars in dough are broken down through
glycolysis
– The resulting release of CO2 causes the bread to
puff up
– The alcohol produced evaporates during baking
– The yeast is killed by the heat.