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Ch. 9 - Cellular Respiration and Fermentation
Freeman - Biological Science 7th Edition
Freeman7th EditionBiological ScienceISBN: 9783584863285Not the one you use?Change textbook
All textbooksFreeman 7th EditionCh. 9 - Cellular Respiration and FermentationProblem 9
Chapter 9, Problem 9

Cyanide (C ≡ N−) blocks complex IV of the electron transport chain. Suggest a hypothesis for what happens to the ETC when complex IV stops working. Your hypothesis should explain why cyanide poisoning in humans is fatal.

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1
Understand the role of complex IV in the electron transport chain (ETC). Complex IV, also known as cytochrome c oxidase, is responsible for the final step of electron transfer to oxygen, forming water. This step is crucial for maintaining the proton gradient across the mitochondrial membrane.
Recognize the impact of cyanide on complex IV. Cyanide binds to the iron within cytochrome c oxidase, inhibiting its function. This prevents the transfer of electrons to oxygen, effectively halting the ETC.
Formulate a hypothesis: If complex IV is blocked by cyanide, electrons cannot be transferred to oxygen, leading to a cessation of ATP production. This is because the proton gradient necessary for ATP synthesis by ATP synthase is disrupted.
Explain the consequences of the hypothesis: Without ATP production, cells cannot perform essential functions, leading to cell death. Since ATP is vital for energy-dependent processes, cyanide poisoning results in rapid organ failure and is fatal.
Consider the broader implications: Cyanide poisoning affects all cells reliant on aerobic respiration, particularly those with high energy demands like neurons and cardiac cells, explaining the rapid onset of symptoms and fatality.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electron Transport Chain (ETC)

The electron transport chain is a series of protein complexes located in the inner mitochondrial membrane that facilitates the transfer of electrons from electron donors to oxygen. This process generates a proton gradient across the membrane, which is used to produce ATP, the cell's energy currency. Disruption of the ETC can halt ATP production, leading to cellular energy failure.
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Complex IV Function

Complex IV, also known as cytochrome c oxidase, is the final enzyme in the electron transport chain. It facilitates the transfer of electrons to oxygen, forming water. This step is crucial for maintaining the proton gradient necessary for ATP synthesis. Inhibition of complex IV prevents electron transfer to oxygen, disrupting ATP production and leading to energy depletion in cells.
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Cyanide Poisoning

Cyanide is a potent inhibitor of complex IV, blocking the electron transport chain and preventing ATP synthesis. Without ATP, cells cannot perform essential functions, leading to rapid cell death. In humans, cyanide poisoning is fatal because it causes widespread energy failure in vital organs, particularly the brain and heart, which rely heavily on aerobic respiration for energy.
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Related Practice
Textbook Question

The researchers who observed that magnetite was produced by bacterial cultures from the deep subsurface carried out a follow-up experiment. These biologists treated some of the cultures with a drug that poisons the enzymes involved in electron transport chains. In cultures where the drug was present, no more magnetite was produced. Does this result support or undermine their hypothesis that the bacteria in the cultures perform cellular respiration? Explain your reasoning.

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Textbook Question
Explain the relationship between electron transport and oxidative phosphorylation. How do uncoupling proteins 'uncouple' this relationship in brown adipose tissue?
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Textbook Question
The researchers who observed that magnetite was produced by bacterial cultures from the deep subsurface carried out a follow-up experiment. These biologists treated some of the cultures with a drug that poisons the enzymes involved in electron transport chains. In cultures where the drug was present, no more magnetite was produced. Does this result support or undermine their hypothesis that the bacteria in the cultures perform cellular respiration? Explain your reasoning.
1232
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Textbook Question

Early estimates suggested that the oxidation of glucose via aerobic respiration would produce 38 ATP. Based on what you know of the theoretical yields of ATP from cellular respiration, show how this total was determined. Why do biologists now think this amount of ATP per molecule of glucose is not achieved in cells?

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