Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 21: Problem 6

(Integrates with Chapter \(20 .\)) In mitochondria, the membrane potential \((\Delta \psi)\) contributes relatively more to \(\Delta p\) (proton-motive force) than does the pH gradient \((\Delta \mathrm{pH})\). The reverse is true in chloroplasts. Why do you suppose that the proton-motive force in chloroplasts can depend more on \(\Delta\) pH than mitochondria can? Why is \((\Delta \psi)\) less in chloroplasts than in mitochondria?

Short Answer

Expert verified
Mitochondria, with their highly impermeable membranes and complex transport proteins, can generate a more substantial membrane potential, while the pH gradient is more influential in chloroplasts due the accumulation of protons in the thylakoid space during photosynthesis. The chloroplast membrane is more permeable to ions, making the generation of a substantial membrane potential more difficult, that's why the proton motive force in chloroplasts can depend more on the pH gradient than the membrane potential.

Step by step solution

01

Understand the Components

Start by understanding the functions of mitochondria and chloroplasts. Mitochondria are the powerhouse of cells, generating ATP through the process of cellular respiration which releases energy stored in glucose. Chloroplasts, in contrast, carry out photosynthesis, a process of converting light energy into chemical energy stored in glucose.
02

Understand Proton-motive force

Understand the concept of proton-motive force. It is the force that promotes movement of protons (hydrogen ions, H+) across a membrane, it depends on two factors, the concentration gradient of protons (pH difference, ΔpH) and the electric potential difference across the membrane (membrane potential, Δψ).
03

Comparisons between Mitochondria and Chloroplasts

For mitochondria, the membrane potential (\(Δψ\)) contributes more to \(Δp\) (proton-motive force) which is due to the electrochemical gradient created by the electron transport chain during cellular respiration. In contrast, in chloroplasts, the pH gradient (\(ΔpH\)) is more influential due to the accumulation of protons in the thylakoid space during photosynthesis.
04

Understand the Differences

In comparison, mitochondria have a highly impermeable membrane and a complex system of transport proteins which allows a more substantial membrane potential generation. On the other hand, the chloroplast membrane is more permeable to ions, making the generation of a substantial membrane potential more difficult. Thus, in chloroplasts, the proton motive force depends more on the pH gradient than the membrane potential.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

The photosynthetic \(\mathrm{CO}_{2}\) fixation pathway is regulated in response to specific effects induced in chloroplasts by light. What is the nature of these effects, and how do they regulate this metabolic pathway?

The overall equation for photosynthetic \(\mathrm{CO}_{2}\) fixation is \\[6 \mathrm{CO}_{2}+6 \mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+6 \mathrm{O}_{2}\\] \(A l l\) the \(\mathrm{O}\) atoms evolved as \(\mathrm{O}_{2}\) come from water; none comes from carbon dioxide. But \(12 \mathrm{O}\) atoms are evolved as \(6 \mathrm{O}_{2}\), and only \(6 \mathrm{O}\) atoms appear as \(6 \mathrm{H}_{2} \mathrm{O}\) in the equation. Also, \(6 \mathrm{CO}_{2}\) have \(12 \mathrm{O}\) atoms, yet there are only \(6 \mathrm{O}\) atoms in \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} .\) How can you account for these discrepancies? (Hint: Consider the partial reactions of photosynthesis: ATP synthesis, NADP' reduction, photolysis of water, and the overall reaction for hexose synthesis in the Calvin-Benson cycle.)

Write a balanced equation for the synthesis of a glucose molecule from ribulose-1,5-bisphosphate and \(\mathrm{CO}_{2}\) that involves the first three reactions of the Calvin cycle and subsequent conversion of the two glyceraldehyde-3-P molecules into glucose.

Plastoquinone oxidation by cytochrome \(b c_{1}\) and cytochrome \(b_{i} f\) complexes apparently leads to the translocation of \(4^{+} / 2 e^{-} .\) If \(\mathscr{E}_{0}^{\prime}\) for cytochrome \(f=0.365 \mathrm{V} \text { (Table } 20.1)\) and \(\mathrm{E}_{\mathrm{o}}^{\prime}\) for \(\mathrm{PQ} / \mathrm{PQH}_{2}=0.07 \mathrm{V},\) calculate \(\Delta G\) for the coupled reaction: \\[2 h v+4 \mathrm{H}^{+}_{\mathrm{in}} \longrightarrow 4 \mathrm{H}_{\mathrm{out}}^{+}\\] (Assume a value of \(23 \mathrm{kJ} / \mathrm{mol}\) for the free energy change \((\Delta G)\) associated with moving protons from inside to outside.

If noncyclic photosynthetic electron transport leads to the translocation of \(3 \mathrm{H}^{+} / e^{-}\) and cyclic photosynthetic electron transport leads to the translocation of \(2 \mathrm{H}^{+} / e^{-},\) what is the relative photosynthetic efficiency of ATP synthesis (expressed as the number of photons absorbed per ATP synthesized) for noncyclic versus cyclic photophosphorylation? (Assume that the \(\mathrm{CF}_{1} \mathrm{CF}_{0}-\mathrm{ATP}\) synthase yields \(3 \mathrm{ATP} / 14 \mathrm{H}^{+}\).)
See all solutions

Recommended explanations on Chemistry Textbooks

Organic Chemistry

Read Explanation

Kinetics

Read Explanation

Nuclear Chemistry

Read Explanation

Physical Chemistry

Read Explanation

Ionic and Molecular Compounds

Read Explanation

Making Measurements

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free