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Fermentation
Do Now 12/18 (HW check 6.7-6.9)
OBJECTIVES:
1. Define oxidation, reduction, and redox; explain how
these reactions occur in metabolism.
2. Describe the processes of ethanolic and lactic acid
fermentation.
TASK:
1. There is a total of about 3,000 kJ of energy stored in
the bonds of one glucose molecule. When a cell
hydrolyzes ATP to ADP, about 50 kJ of energy is
released. What is the approximate energy efficiency
(%) of glycolysis?
Redox Reactions
Redox: LEO the Lion Says GER.
• The Loss of Electrons is Oxidation; the
Gain of Electrons is Reduction.
• Whenever something is oxidized,
something else must be reduced (i.e. the
electrons have to go somewhere!)
• In fermentation, NADH is oxidized, and
pyruvate is reduced.
Adding Oxygen to Carbon Releases
Energy
• Respiration oxidizes carbon; the more the
carbon gets oxidized, the more energy is
released.
Compound
Carbon is
H:O Ratio
Amount of energy
stored in molecule
CH4
Fully Reduced
4:0
High
C6H12O6 (Glucose)
C3H4O3 (Pyruvate),
C2H4O (Ethanol),
C3H6O3 (Lactic Acid)
Partially oxidized 4:1 – 4:3
Moderate
CO2
Fully Oxidized
Low
0:4
Lactic Acid Fermentation – you do
this!
Notice: No CO2 produced.
NADH is oxidized to NAD+
Pyruvate is reduced to lactic acid.
Fermentation: To recycle NAD+
The top section is
glycolysis.
The bottom is
ethanolic
fermentation.
Alcoholic Fermentation Ethanol and CO2
are the waste
products
Fermentation is
Wasteful
• The products of
fermentation
(ethanol or lactic
acid) contain
MORE energy than
pyruvate!
• The NADH used
loses valuable
energy – in
anaerobic
conditions anyway.
So Why Do They Do it?
• The electrons ripped from food have to go
somewhere!
• In aerobic respiration they eventually end up in
water after being attached to oxygen.
• When there’s no oxygen around, the cell
deposits the electrons on what’s available: the
leftovers from glycolysis.
• This is ONE of the ways in which aerobic
respiration is more efficient than anaerobic.
Yummy Yummy Fermentation
• In addition to making lots of yummy food
products from soy sauce to kimchi,
fermentations done by engineered
microbes can produce useful enzymes or
drugs!
Other Notable Types of
Fermentation
Recap
• Fermentation is the second step in anaerobic
respiration; its function is to recycle the NAD+
needed for glycolysis to continue.
• Alcoholic fermentation (like done by yeast)
produces CO2 and ethanol. Lactic acid
fermentation (like done by human muscle cells)
produces lactic acid. There are many other
types as well.
• Fermentation is inefficient: the waste products
of glycolysis are REDUCED by NADH, which
adds chemical energy to them.