Campbell Biology - Modified Mstingbiology
Campbell Biology - Modified Mstingbiology
10th Edition
ISBN: 9780321935311
Author: Reece
Publisher: PEARSON
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Textbook Question
Chapter 9, Problem 9.1CR

Describe the difference between the two processes in cellular respiration that produce ATP: oxidative phosphorylation and substrate-level phosphorylation.

Expert Solution & Answer
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Summary Introduction

To review: The two processes of cellular respiration (oxidative phosphorylation and substrate- level phosphorylation) that produce ATP and differentiate between them.

Concept introduction: Generally, in cellular respiration, “phosphorylation” refers to the phosphate group shift from a compound for ATP synthesis. Oxidative phosphorylation and substrate-level phosphorylation are two types of phosphorylation processes that occur inside the living organisms for the production of energy. 

Explanation of Solution

Differences between oxidative phosphorylation and substrate-level phosphorylation:

S. No. Oxidative phosphorylation Substrate-level phosphorylation
1. It occurs in the electron transport chain and accounts for the 90% synthesis of ATP. Substrate-level phosphorylation takes place in glycolysis, citric acid cycle, and accounts for the production of smaller amount of ATP.
2. Chemiosmosis is a process in which chemical energy is transformed by electron transport chain to a form that can be used for ATP synthesis. Used in fermentation along with catabolizing an organic compound to produce ATP.
3. ATP is generated from the oxidation of NADH and FADH2 and the subsequent transfer of electrons and pumping of protons. It occurs if there is a reaction that releases sufficient energy to allow the direct phosphorylation of ADP.

Refer to Fig 9.6, “An overview of cellular respiration” in the textbook, which shows that NADH and FADH2 are generated during the first two stages of the redox reactions of the glycolysis and citric acid cycle.

The electrons from NADH and FADH2 are accepted from the electron transport chain in the third stage of respiration.

At the final stage of electron transport chain, oxygen and hydrogen ions bind with electrons to form water. The mitochondria store the released energy at each of the step of electron transport chain and an inorganic phosphate is added to ADP to form ATP.

Refer to Fig.9.7, “Substrate-level phosphorylation” in the textbook. In the substrate-level phosphorylation, an enzyme catalyzes the transfer of a phosphate group from an organic substance to ADP to form an ATP. The ATP production in the glycolysis takes place due to substrate-level phosphorylation and also during one of the steps in the citric acid cycle.

Conclusion
Most of the energy from the cellular respiration is derived from oxidative phosphorylation. Glycolysis and Citric acid cycle releases energy which enters the electron transport chain and chemiosmosis to make ATP. In the substrate-level phosphorylation, a phosphate group is transferred by an enzyme to ADP from an intermediate substrate and synthesizes ATP.

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Chapter 9 Solutions

Campbell Biology - Modified Mstingbiology

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