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Chapter 27

BI110 Chapter Notes - Chapter 27: Electron Acceptor, Anaerobic Respiration, Facultative Anaerobic Organism

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Matthew Smith

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Module 27 Fermentation and Anaerobic Respiration
Anaerobic Respiration: Using Terminal Electron Acceptors Other Than Oxygen
In the absence of oxygen, other substances serve as the terminal electron acceptor for
the redox reactions of cellular respiration
Anaerobic respiration uses an ETC to oxidize NADH and FADH2 to NAD+ and FAD.
Anaerobic organisms have specialized enzymes that allow substances such as CO2,
nitrate, iron, and sulfate to serve as the terminal electron acceptor. These molecules not
as electronegative as O2, cannot extract as much energy from glucose oxidation as
aerobic respiration (75%)
Fermentation Allows Glycolysis to Continue in the Absence of Terminal Electron
Fermentation couples oxidation of NADH to NAD+ with the reduction of pyruvate.
Fermentation allows glycolysis to continue uninterrupted by regenerating NAD+, can
accept more electrons from reactions of glycolysis
Numerous fermentation pathways. One of the pathways is lactic acid fermentation,
oxidation of NADH to NAD+ is coupled to reduction of pyruvate to lactic acid. Lactic acid
fermentation is a one-step process: pyruvate directly reduced to lactic acid
Alcoholic fermentation converts pyruvate to ethanol and CO2 in a two-step process. The
3-carbon molecule of pyruvate converted into 2-cabron molecule of acetaldehyde,
releasing CO2. Acetaldehyde reduced to ethanol, NADH oxidized to NAD+
Why does fermentation produce less ATP than respiration does?
Because the end products of fermentation still contain most of the stored energy of the
starting material.
Some organisms prefer oxygen and some avoid it.
Obligate Aerobes organisms or cells that require oxygen because oxygen is the only
terminal acceptor they can use
Obligate Anaerobes organisms killed by the presence of oxygen
Facultative Anaerobes can survive in the presence or absence of oxygen
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