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Chapter 21: Problem 26

Obeying the laws of thermodynamics. Why will isolated \(\mathrm{F}_{1}\) subunits display ATPase activity but not ATP synthase activity? How can the enzyme then function as ATP synthase in mitochondria?

Short Answer

Expert verified
Isolated F鈧� subunits lack proton motive force, so they can't synthesize ATP; in mitochondria, they synthesize ATP via the proton gradient-driven F鈧�F鈧� complex.

Step by step solution

01

Understanding Isolated F鈧� Subunits

In an isolated state, the F鈧� subunit of ATP synthase can perform ATP hydrolysis, which means it acts as an ATPase. This is because, in isolation, there is no proton motive force (pmf) to drive ATP synthesis.
02

Role of Proton Motive Force

In mitochondria, ATP synthesis by the F鈧� subunit is powered by the proton gradient (proton motive force) across the inner mitochondrial membrane. This gradient is created by the electron transport chain and provides the necessary energy for ATP synthesis.
03

Integration with F鈧� Subunit

In its normal working environment within the mitochondrion, the F鈧� subunit is attached to the F鈧� subunit, forming the F鈧�F鈧� ATP synthase complex. The F鈧� subunit acts as a channel through which protons travel down their gradient, providing the energy required for the F鈧� subunit to catalyze the synthesis of ATP from ADP and inorganic phosphate.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

F鈧� subunit
The F鈧� subunit is an essential part of ATP synthase, a critical enzyme for cellular energy production. In isolated conditions, the F鈧� subunit shows ATPase activity, meaning it can break down ATP into ADP and inorganic phosphate. This activity occurs because, in isolation, the energy needed for ATP synthesis isn't available. The F鈧� subunit lacks the driving force required to put together the energy-rich ATP molecule. However, when functioning properly within mitochondria, it becomes a part of a larger mechanism that enables it to synthesize ATP.
Proton Motive Force
The proton motive force (pmf) is a form of energy that is harnessed during cellular respiration. It is generated by pumping protons (H鈦� ions) across the inner mitochondrial membrane, creating a gradient. This electrochemical gradient is a crucial energy source. It powers the ATP synthase enzyme to produce ATP from ADP and phosphate. The flow of protons back across the membrane through ATP synthase is what drives the transformation process. Without this force, ATP synthase cannot synthesize ATP effectively.
Mitochondria
Mitochondria are often referred to as the powerhouse of the cell. They are the organelles where ATP synthesis takes place. Inside the mitochondria, the electron transport chain creates the proton motive force by transferring protons across the inner membrane. This setup creates a potential energy source that ATP synthase uses to generate ATP. The unique structure of mitochondria, with its folded inner membrane, helps maintain the environment needed for efficient energy conversion.
F鈧�F鈧� ATP synthase complex
The F鈧�F鈧� ATP synthase complex is a sophisticated molecular machine that plays a crucial role in producing cellular energy. It consists of two main subunits: F鈧� and F鈧�.
  • The F鈧� subunit acts as a channel, allowing protons to flow back into the mitochondrial matrix.
  • The F鈧� subunit catalyzes the synthesis of ATP from ADP and inorganic phosphate.
The cooperation between these subunits enables ATP synthase to channel the energy derived from the proton motive force into the production of ATP. This intricate process is essential for maintaining energy levels within the cell, supporting various cellular functions.

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Most popular questions from this chapter

Runaway mitochondria \(1 .\) The number of molecules of inorganic phosphate incorporated into organic form per atom of oxygen consumed, termed the \(P: O\) ratio, was frequently used as an index of oxidative phosphorylation. Suppose that the mitochondria of a patient oxidize NADH irrespective of whether ADP is present. The \(P: O\) ratio for oxidative phosphorylation by these mitochondria is less than normal. Predict the likely symptoms of this disorder.

Alternative routes. The most common metabolic sign of mitochondrial disorders is lactic acidosis. Why?

The same, but different. Why is the electroneutral exchange of \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) for \(\mathrm{OH}^{-}\) indistinguishable from the electroneutral symport of \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) and \(\mathrm{H}^{+} ?\)

With sympathy. Predict the effect on ATP synthesis if the \(\mathbf{b}\) and \(\delta\) subunits of the ATPase were absent.

A question of coupling. What is the mechanistic basis for the observation that the inhibitors of ATP synthase also lead to an inhibition of the electron- transport chain?
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