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7.9 The Citric Acid Cycle Releases Much More Free Energy Than Glycolysis Does

Electron carriers (NAD in glycolysis; NAD and FAD in the citric acid cycle) are reduced and ATP is generated in reactions coupled to other reactions, producing major drops in free energy as metabolism proceeds.

goal of oxidizing two acetyl groups to two molecules of

CO2?" There are three reasons:

► First, the cycle includes molecules that have other roles in the cell. As we will see later in this chapter, the intermediates of the citric acid cycle are themselves catabolic (breakdown) products or anabolic (synthesis) building blocks of other molecules, such as amino acids and nucleotides.

► Second, the citric acid cycle is far more efficient at harvesting energy from acetyl CoA than any single reaction could be.

► Third, evolution is a conservative, add-on process. It rarely operates by inventing an entirely new process.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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