Download - AP Bio Ch. 9 Anaerobic respiration
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Anaerobic Respiration
How cells make ATP in the absence of oxygen
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Fermentation Allows Cells to Make ATP Without Using Oxygen
Glucose
Glycolysis
Oxygen Present Oxygen Absent
Citric Acid Cycle
Oxidative Phosphorylation
Fermentation
Alcohol Lactic Acid
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Remember…
Glycolysis happens in the cytosol
It does not require the presence of oxygen
NAD+ acts as the electron acceptor
2 ATP are generated 2 NADH are
generated
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Fermentation
An extension of glycolysis
Cells can use this step of respiration to keep up the ATP supply
But…must have a steady supply of NAD+ to act as the electron acceptor
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•Unlike aerobic respiration, fermentation generates ATP through substrate-level phosphorylation
•Fermentation can only continue if there’s a supply of the oxidizing agent NAD+ to be used in glycolysis
After NADH is produced from glycolysis,its electrons are transferred to pyruvate. This regenerates the NAD+ that can again be used for another round of glycolysis.
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In contrast…
In aerobic respiration - the supply of NAD+ is continually renewed as the NADH molecules deliver their electrons to the electron transport chain
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Fermentation
In anaerobic respiration, we need another way to recycle NAD+
Instead, the electrons in NADH are transferred to pyruvate, the end product of glycolysis
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LE 9-18
Pyruvate
Glucose
CYTOSOL
No O2 presentFermentation
Ethanolor
lactate
Acetyl CoA
MITOCHONDRION
O2 present Cellular respiration
Citricacidcycle
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So fermentation is…
Glycolysis (2 ATP, 2 NADH, pyruvate)
PLUSExtra reactions that oxidize the NADH to
NAD+ by transferring electrons to pyruvate
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2 main types of fermentation
Alcohol fermentation
Lactic acid fermentation
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There Are 2 Types of Fermentation
Alcohol Fermentation•Glycolysis makes pyruvate•CO2 is released from pyruvate.
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Alcohol fermentation
Occurs in yeast and many bacteria
Pyruvate (3 carbons) converted to acetaldehyde (2 carbons) and CO2 is
released (used in baking to make bread rise)
Acetaldehyde is reduced by NADH to ethanol, thus regenerating the supply of NAD+
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Lactic Acid Fermentation
Occurs in muscle cells, some bacteria, some fungi
Pyruvate is reduced by NADH to lactic acid, thus regenerating the supply of NAD+
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Muscle Cells
When muscles are working hard, they quickly exhaust the supply of oxygen to the cell
The cell launches into fermentation to keep up
Lactic acid accumulates in cells leading to cramps
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Facultative Anaerobes
Organisms that can survive using either anaerobic or aerobic respiration
Yeast
Bacteria
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Main differences between aerobic and anaerobic respiration Aerobic
Final electron acceptor - oxygenNAD+ regenerated
when electrons delivered to ETCHuge energy payoff -
38 ATP, glucose fully broken down through Citric Acid cycle
AnaerobicFinal electron acceptor
- pyruvate or acetaldehydeNAD+ regenerated
when electrons given to pyruvate or acetaldehydeLess energy payoff - 2
ATP, energy still trapped in pyruvate or ethanol
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Ancient prokaryotes probably used glycolysis to make ATP
What is the basis for this statement??
•The oldest prokaryotes were around before there was sufficient oxygen in the atmosphere
•Glycolysis is the most widespread metabolic pathway among organisms
•Glycolysis occurs in the cytosol…..prokaryotes don’t have organelles
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Glycolysis and the Citric Acid Cycle Connect to Many Other Metabolic Pathways
Many molecules aside from glucose can be used in cellular respiration to make ATP:
The monomers of different molecules begin the process at different steps
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The energy in organic molecules, which is used to power the cell, is released, but not produced during cellular respiration.