From the Guidelines
The proton gradient is used to drive ATP synthesis by ATP synthase during oxidative phosphorylation. This process occurs in the mitochondria, where the energy from food molecules is converted into a usable form of energy, ATP 1. During cellular respiration, electrons from food molecules are transferred through the electron transport chain in the inner mitochondrial membrane, powering the pumping of protons (H+ ions) from the mitochondrial matrix into the intermembrane space, creating a concentration gradient.
- The resulting electrochemical gradient represents stored energy, as protons have a natural tendency to flow back into the matrix.
- ATP synthase, a large protein complex embedded in the inner membrane, harnesses this energy as protons flow through it down their concentration gradient.
- This flow causes the rotation of parts of the ATP synthase enzyme, which mechanically drives the synthesis of ATP from ADP and inorganic phosphate, as described in the study published in Clinical Nutrition 1. The energy metabolism consists of three steps:
- the release of hydrogen from water and nutrients
- production of a proton gradient during cellular respiration
- production of ATP by consumption of this proton gradient 1. This process is a fundamental mechanism of energy conversion in cells, transforming the energy from food into the usable form of ATP through the intermediate of a proton gradient.
From the Research
Proton Gradient in Oxidative Phosphorylation
- The proton gradient is utilized by proton translocating ATP synthases to catalyze the synthesis of ATP from ADP and P(i) 2.
- The energy accumulated in the proton gradient is used by complex V (ATP synthase) to produce ATP 3.
- The proton gradient drives ATP synthesis by ATP synthase, which is the correct answer.
Incorrect Options
- It transports electrons to oxygen: This is not the primary function of the proton gradient in oxidative phosphorylation 4, 5.
- It directly oxidizes glucose: The proton gradient is not directly involved in the oxidation of glucose 4, 5.
- It breaks down fatty acids: The proton gradient is not directly involved in the breakdown of fatty acids 4, 5.
Mechanism of ATP Synthesis
- The synthesis of ATP by H(+)-ATP synthases proceeds without the formation of a phosphorylated enzyme intermediate, and involves co-operative interactions between the catalytic subunits 2.
- The kinetic coupling of the respiratory chain with ATP synthase, but not proton gradients, drives ATP production in cristae membranes 6.