Ch. 9 - Cellular Respiration and Fermentation

Campbell - Campbell Biology 11th Edition

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Urry 11th Edition

Ch. 9 - Cellular Respiration and Fermentation

Problem 9

Chapter 9, Problem 9

The proton pump shown in Figures 7.17 and 7.18 is a type of ATP synthase (see Figure 9.14). Compare the processes shown in the two figures, and say whether they are involved in active or passive transport (see Concepts 7.3 and 7.4).

Verified step by step guidance

Begin by examining Figures 7.17 and 7.18, which depict a proton pump. This pump is a type of ATP synthase, an enzyme that facilitates the synthesis of ATP from ADP and inorganic phosphate.

Understand that ATP synthase operates by using a proton gradient across a membrane. This gradient is established by the active transport of protons, which requires energy input, typically from ATP hydrolysis.

Compare the proton pump mechanism to the ATP synthase process shown in Figure 9.14. Note that ATP synthase uses the energy from the proton gradient to synthesize ATP, which is a form of passive transport as it does not require direct energy input.

Identify the type of transport involved in each process. The proton pump actively transports protons across the membrane, creating a gradient, which is an example of active transport. In contrast, ATP synthase utilizes this gradient to produce ATP, representing passive transport.

Conclude by summarizing that the proton pump is involved in active transport, while ATP synthase is involved in passive transport, as it harnesses the energy from the established gradient without direct energy expenditure.

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Key Concepts

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

Proton Pump

A proton pump is a membrane protein that moves protons (H+ ions) across a biological membrane, creating a proton gradient. This process is typically active transport, requiring energy, often from ATP, to move protons against their concentration gradient, which is crucial for processes like ATP synthesis in cellular respiration.

ATP Synthase

ATP synthase is an enzyme that synthesizes ATP from ADP and inorganic phosphate, using the energy derived from the flow of protons down their concentration gradient. This process is part of chemiosmosis and is considered passive transport, as it harnesses the potential energy stored in the proton gradient without directly using ATP.

Active vs Passive Transport

Active transport involves the movement of molecules across a membrane using energy, typically from ATP, to move substances against their concentration gradient. In contrast, passive transport relies on the natural diffusion of molecules down their concentration gradient, requiring no energy input, as seen in processes like facilitated diffusion and osmosis.

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Passive vs. Active Transport

Related Practice

Textbook Question

Most CO₂ from catabolism is released during

a. Glycolysis.

b. The citric acid cycle.

c. Lactate fermentation.

d. Electron transport.

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Textbook Question

This computer model shows the four parts of ATP synthase, each part consisting of a number of polypeptide subunits (the solid gray part is still an area of active research). Using Figure 9.13 as a guide, label the rotor, stator, internal rod, and catalytic knob of this molecular motor.

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Textbook Question

Step 3 in Figure 9.8 is a major point of regulation of glycolysis. The enzyme phosphofructokinase is allosterically regulated by ATP and related molecules (see Concept 8.5). Considering the overall result of glycolysis, would you expect ATP to inhibit or stimulate activity of this enzyme? Explain.

(Hint: Make sure you consider the role of ATP as an allosteric regulator, not as a substrate of the enzyme.)

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Textbook Question

When electrons flow along the electron transport chains of mitochondria, which of the following changes occurs?

a. The pH of the matrix increases.

b. ATP synthase pumps protons by active transport.

c. The electrons gain free energy.

d. NAD⁺ is oxidized.

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