Download Chapter 9.5 and 9.6

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Fermentation: a catabolic process that
makes a limited amount of ATP from
glucose without an electron transport
chain and that produces a
characteristic end product, such as ethyl
alcohol or lactic acid
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Fermentation provides a mechanism by
which some cells can oxidize organic
fuel and generate ATP without using
oxygen.
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Oxidation refers to the loss of electrons to
any electron acceptor, not just oxygen.
http://www.youtube.com/watch?v=AFLu6lhF1YI
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Glycolysis…
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Is an exergonic process
Has an oxidizing agent that is NAD+
Produces 2 molecules of pyruvate
2 ATP molecules result from substrate-level
phosphorylation
Can be aerobic or anaerobic
› Aerobic: containing oxygen
› Anaerobic: lacking oxygen (an- means without)
 Electrons from NADH are passed to pyruvate,
regenerating the NAD+ required to keep cycle
running.
 Cycle shuts down if lacking an oxidizing agent
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Alcohol Fermentation: the conversion of
pyruvate to acetaldehyde, releasing carbon
dioxide, and then reduced to ethyl alcohol
*Ex: yeast used for brewing beer,
baking bread
Lactic Acid Fermentation: the conversion of
pyruvate to lactate with no release of carbon
dioxide
*Ex: fungi cultured commerically for
yogurt and cheese
-lactic acid in muscles after strenuous
exercise
http://leavingbio.net/RESPIRATION-(higher%20level).htm
Located on
page 175
http://www.meth
uen.k12.ma.us/m
nmelan/chapter_
9_cellular_respirati
on.htm
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Similarities
› Both use glycolysis to oxidize glucose
› NAD+ is the oxidizing agent
› Both are catabolic reactions to harvest energy
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Differences
› Contrasting mechanisms for oxidizing NADH to NAD+
› In fermentation, the final electron acceptor is an
organic molecule (like pyruvate or acetaldehyde).
› In cellular respiration, the final electron acceptor is
oxygen.
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Respiration yields as much as 19 times more
ATP per glucose than fermentation.
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Facultative anaerobes: an organism that
makes ATP by aerobic respiration if oxygen
is present but that switches to fermentation
under anaerobic conditions
› Example: our muscle cells
› Pyruvate is a fork in the road…
›  pyruvate converts to acetyl CoA
›  pyruvate is diverted from the citric acid cycle
and serves as an electron acceptor to recycle
NAD+
Glycolysis occurs in nearly all organisms
and most likely evolved in ancient
prokaryotes before there was oxygen in
the atmosphere.
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Free glucose molecules are not common in the
diets of humans or animals.
Catabolic pathways funnel electrons from
many kinds of organic molecules into cellular
respiration.
Glycolysis can accept a wide range of
carbohydrates for catabolism.
Examples:
› Starch is hydrolyzed to glucose, which can be broken
down by glycolysis and the citric acid cycle.
› Glycogen can also be hydrolyzed to glucose
between meals as fuel for respiration.
Beta oxidation: a metabolic sequence
that breaks fatty acids down to twocarbon fragments that enter the citric
acid cycle as acetyl CoA
 Fats make excellent fuel.

› A gram of fat oxidized by respiration
produces more than twice as much ATP as a
gram of carbohydrate.
Page 177
http://www.meth
uen.k12.ma.us/m
nmelan/chapter_
9_cellular_respirati
on.htm
Cells need substance as well as energy.
In addition to calories, food must also
provide the carbon skeletons that cells
require to make their own molecules
 The body can use smaller molecules from
food directly or use them to build other
substances through glycolysis or the citric
acid cycle.
 Glycolysis and the citric acid cycle function
as metabolic interchanges that enable
cells to convert some kinds of molecules to
others as we need them.
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The cell doesn’t waste energy making more
of a particular substance than it needs.
 The most common mechanism for this
control is feedback inhibition: the end
product of the anabolic pathway inhibits
the enzyme that catalyzes an early step of
the pathway
 Cellular respiration is controlled by allosteric
enzymes at key points in glycolysis and the
citric acid cycle.
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Feedback Regulation of Respiration
The cells control catabolism.
 When there is plenty of ATP to meet
demand, respiration slows down.
 An important switch is
phosphofructokinase, which is the
enzyme that catalyzes step 3 of
glycolysis.
 Phosphofructokinase: an allosteric
enzyme with receptors for specific
inhibitors and activators
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