ATP Synthesis and Chemiosmosis: Proton and Electrochemical Gradients

Overview

Recall questions on Proton and Electrochemical Gradients.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   In a mitochondrion, from which compartment to which compartment are protons pumped?

   Model answer

   Protons are pumped from the matrix across the inner membrane into the intermembrane space.

2. 2

   In a chloroplast, where do the protons accumulate?

   Model answer

   They accumulate inside the thylakoid space, having been pumped there from the stroma.

3. 3

   State two ways in which the membranes of mitochondria and chloroplasts are functionally similar.

   Model answer

   Both hold an electron transport chain that pumps protons into an enclosed compartment, and both are impermeable to protons except through ATP synthetase, so both can generate and then use a proton gradient to make ATP.

4. 4

   Why must the membrane across which the proton gradient forms be impermeable to protons?

   Model answer

   If protons could leak back freely the gradient would collapse, and their return would not be forced through ATP synthetase, so no ATP would be made.

5. 5

   What is the advantage of the inner mitochondrial membrane being folded into cristae?

   Model answer

   The folding provides a large surface area for many electron carriers, proton pumps and ATP synthetase molecules, so the rate of ATP synthesis is high.

6. 6

   What supplies the energy needed by the proton pumps?

   Model answer

   The energy comes from the potential energy carried by excited, high-energy electrons as they pass along the electron transport chain.

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