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Ch.21 The Generation of Biochemical Energy
McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoMcMurry 8th EditionCh.21 The Generation of Biochemical EnergyProblema 5
Capitolo 21, Problema 5

A common metabolic strategy is the lack of reactivity—that is, the slowness to react—of compounds whose breakdown is exergonic. For example, hydrolysis of ATP to ADP or adenosine monophosphate (AMP) is exergonic but does not take place without an appropriate enzyme present. Why would the cell use this metabolic strategy?

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1
Understand the concept of exergonic reactions: Exergonic reactions release energy as they proceed. The hydrolysis of ATP to ADP or AMP is an example of an exergonic reaction, meaning it releases energy that can be used by the cell for various processes.
Recognize the role of enzymes in metabolic reactions: Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for the reaction to occur. Without enzymes, even exergonic reactions may proceed very slowly or not at all.
Consider the importance of controlled energy release: If exergonic reactions like ATP hydrolysis occurred spontaneously and uncontrollably, the cell would lose energy in an unregulated manner, leading to inefficiency and potential damage to cellular structures.
Understand the metabolic strategy: By requiring enzymes to catalyze the hydrolysis of ATP, the cell ensures that energy release is tightly regulated and occurs only when and where it is needed. This allows the cell to efficiently harness the energy for specific processes such as muscle contraction, active transport, or biosynthesis.
Conclude the reasoning: The lack of reactivity of compounds like ATP without enzymes is a protective mechanism. It prevents wasteful or harmful energy release and ensures that the cell maintains control over its metabolic processes, promoting efficiency and stability.

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Exergonic Reactions

Exergonic reactions are chemical processes that release energy, typically in the form of heat or work, as they proceed. In the context of metabolism, these reactions are crucial because they provide the energy necessary for cellular functions. However, despite being energetically favorable, they may not occur spontaneously without the presence of catalysts, such as enzymes, which lower the activation energy required for the reaction.
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Enzyme Catalysis

Enzymes are biological catalysts that accelerate chemical reactions in living organisms by lowering the activation energy barrier. This allows metabolic reactions, including the hydrolysis of ATP, to occur at a rate sufficient for cellular processes. Without enzymes, many exergonic reactions would proceed too slowly to support life, highlighting the importance of these proteins in metabolic pathways.
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Metabolic Regulation

Metabolic regulation refers to the mechanisms that control the rate and direction of metabolic pathways in response to the cell's needs and environmental conditions. By using enzymes to regulate exergonic reactions, cells can prevent uncontrolled energy release, ensuring that energy is released in a controlled manner and utilized effectively for various cellular activities, thus maintaining homeostasis.
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Domanda del libro di testo

The hydrolysis of acetyl phosphate to give acetate and hydrogen phosphate ion has ∆G = -10.3 kcal/mol (-43.1 kJ/mol). Combine the equations and ∆G values to determine whether coupling of this reaction with phosphorylation of ADP to produce ATP is favorable. (You need give only compound names or abbreviations in the equations.)

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Domanda del libro di testo

Which of the following is found in the coenzyme FAD?

a. Two heterocyclic rings

b. ADP

c. A substituted benzene ring

d. A phosphate anhydride bond

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Domanda del libro di testo

The overall equation in this section,

shows the cycle between photosynthesis and oxidation. Pathways operating in opposite directions cannot be exergonic in both directions.

a. Which of the two pathways in this cycle is exergonic and which is endergonic?

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Domanda del libro di testo

Acetyl phosphate, whose structure is given here, is another compound with a relatively high free energy of hydrolysis.

Using structural formulas, write the equation for the hydrolysis of this phosphate.

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Domanda del libro di testo

One of the steps in lipid metabolism is the reaction of glycerol (1,2,3-propanetriol, HOCH2CH(OH)CH2OH, with ATP to yield glycerol 1-phosphate. Write the equation for this reaction using the curved arrow symbolism.

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