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Chapter 9

BIL 150 Chapter Notes - Chapter 9: Anaerobic Respiration, Biofuel, Acetaldehyde


Department
Biology
Course Code
BIL 150
Professor
Gaines Michael
Chapter
9

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Chapter 9: Cellular Respiration and Fermentation
Fermentation is a partial degradation of sugars or other organic fuel that
occurs without the use of oxygen
oImportant points on anaerobic respiration:
A net of 2 ATP is produced from glycolysis
The 2 NADH produced in glycolysis are used to convert
pyruvic acid to ethanol or lactic acid
It occurs in the cytosol of the cell
oPyruvate is converted to ethanol in two steps
First, the carbon dioxide is released from the pyruvate, which
is converted to the two-carbon acetaldehyde
In the second step, acetaldehyde is reduced by NADH to
ethanol
oDuring lactic acid fermentation, pyruvate is reduced directly by
NADH to form lactate as an end produce, with no release of carbon
dioxide
The most efficient catabolic process is aerobic respiration, in which
oxygen is consumed as a reactant along with the organic fuel
oThe cells of most eukaryotic and many prokaryotic organisms can
carry out aerobic respiration
Some prokaryotes use substances other than oxygen as reactants in a
similar process that harvests chemical energy without oxygen called
anaerobic respiration

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The Principle of Redox
oIn many chemical reactions, there is a transfer of one or more
electrons (e-) from one reactant to another and these electron
transfers are called oxidation-reduction reactions, or redox
reactions
Loss of electrons from one substance = oxidation
The addition of electrons to a substance = reduction
The electron donor is called the reducing agent and the
electron acceptor is called the oxidizing agent
Cellular respiration does not oxidize glucose in a single explosive step but
rather in a series of steps, each one catalyzed by an enzyme
oAt key steps, electrons are stripped from the glucose
oEach electron travels with a proton (hydrogen atom)
oThe hydrogen atoms are not transferred directly to oxygen, but
instead are usually passed first to an electron carrier, a coenzyme
called NAD+

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NAD+ is well suited as an electron carrier because it can
cycle easily between oxidized (NAD+) and reduced (NADH)
states
As an electron acceptor, NAD +
functions as an oxidizing
agent during respiration
NAD+ is the most versatile electron acceptor in cellular
respiration and function in several of the redox steps during
the breakdown of glucose
oElectrons lose very little of their potential energy when they are
transferred from glucose to NAD+, and each NADH molecule
formed during respiration represents stored energy
Glycolysis, which occurs in the cytosol, begins the degradation process
by breaking glucose into molecules of a compound called pyruvate
oGlycolysis can be divided into two phases: the energy investment
phase and the energy payoff phase
oDuring the energy investment phase the cell actually spends ATP
oThis investment is repaid with interest during the energy payoff
phase, when ATP is produced by substrate-level phosphorylation
and NAD+ is reduced to NADH by electrons released from the
oxidation of glucose
oAll of the carbon originally present in glucose is accounted for in the
two molecules of pyruvate, no carbon is released as CO2 during
glycolysis
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