Chemiosmotic Hypothesis: Definition, Process, Examples, Theory, Structure & Process

What Is The Chemiosmotic Hypothesis?

Chemiosmosis is a hypothesis put forth by Peter Mitchell in 1961, stating that in both mitochondria and chloroplasts, ATP is generated as a result of the movement of protons across a membrane to create a proton gradient, which drives the enzyme ATP synthase, producing ATP from ADP and inorganic phosphate.

Cellular Respiration And Photosynthesis Overview

Cellular respiration is a metabolic process in which biochemical energy is turned into adenosine triphosphate, producing by-products. Three main processes underlying cellular respiration are glycolysis, the citric acid cycle, and the electron transport chain. The primary sites for all these processes are mitochondria, and the overall process is important for supplying energy to the cells while using oxygen and producing carbon dioxide, water, and ATP.

Photosynthesis is a process whereby green plants, algae, and some bacteria use energy from light to synthesize chemical energy in the form of glucose. The process takes place in the chloroplasts and consists of two major steps: light-dependent reactions, producing ATP and NADPH, and the Calvin cycle, which finally produces glucose from carbon dioxide and water.

Mechanisms Of The Chemiosmotic Hypothesis

The mechanism of the chemiosmotic hypothesis includes following steps:

Step 1 – Electron Transport Chain (ETC)

• A series of protein complexes in the inner mitochondrial membrane.

• The electron from NADH and FADH2 is passed on to oxygen.

• During this process, energy is liberated to pump protons across the membrane, developing a proton gradient.

Process of ETC

• NADH and FADH2 donate electrons to the electron transport chain.

• The electrons flow through complexes I, II, III, and IV.

• The energy liberated from these electrons pumps protons from the mitochondrial matrix into the intermembrane space.

• At the end of the chain, oxygen accepts electrons to form water.

Key Complexes and Roles

Step 2 – Formation Of Proton Gradient

• The intermembrane space becomes flooded with protons.

• Creates an electrochemical gradient that will become the proton motive force.

• Energy from electron transfer drives the pumping of protons across the inner mitochondrial membrane.

Step 3 – ATP Synthesis By ATP Synthase

• ATP synthase uses the proton gradient to produce ATP. Protons flow back into the mitochondrial matrix through ATP synthase.

• This flow is what drives the conversion of ADP and inorganic phosphate into ATP.

• Enzyme synthesize ATP by energy from the proton motive force.

Importance Of The Proton Gradient

The importance of the proton gradient is:

• Stores potential energy used to power ATP synthase which is essential for ATP production in cellular respiration.

• The flow of protons through ATP synthase provides the energy required to drive the phosphorylation of ADP.

• Maintains energy efficiency in both processes, respiration and photosynthesis.

• Explains how light is converted into chemical energy in plants.

Chemiosmotic Hypothesis In Cellular Respiration

The chemiosmotic hypothesis in cellular respiration:

• Explains how ATP is produced within mitochondria, in cellular respiration, .

• Protons move into the intermembrane space, generating the proton motive force.

• Protons flow back via ATP synthase, driving the formation of ATP

• Equation: NADH + O2 + ADP + Pi → NAD+ + H2O + ATP

Chemiosmotic Hypothesis In Photosynthesis

The chemiosmotic hypothesis in photosynthesis:

• A proton gradient in the thylakoid membrane drives the process of ATP synthesis.

• Protons are pumped into the thylakoid membrane.

• The return of electron flow through ATP synthase from ATP

• Equation: Light + ADP + Pi → ATP

Significance Of The Chemiosmotic Hypothesis

The significance of the chemiosmotic hypothesis is that:

• Explains the energy conversion efficiency in mitochondria and chloroplasts.

• Made the concept of ATP generation in all living organisms universal.

• Supports photosynthetic light reactions and oxidative phosphorylation.

• Acts as a foundation for modern day bioenergetics.

Chemiosmotic Hypothesis NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Mechanism of chemiosmotic hypothesis

• Chemiosmotic pathway in Respiration and Photosynthesis

Practice Questions for NEET

Q1. In mitochondria, protons accumulate in the

1. Intermembrane space

2. Matrix

3. Outer membrane

4. Inner membrane

Correct answer: 1) Intermembrane space

Explanation:

In mitochondria, protons accumulate in the intermembrane space. The intermembrane space is the space between the inner and outer membranes of mitochondria. Protons are transported from the matrix to the membrane space to generate proton energy.

Hence, the correct answer is option 1) Intermembrane space.

Q2. NADP reductase enzyme is located on the

1. Lumen side of thylakoid membrane

2. Stroma side of thylakoid membrane

3. Stroma lamellae of chloroplasts

4. Both lumen and stroma sides of the thylakoid membrane.

Correct answer: 2) Stroma side of thylakoid membrane

Explanation:

The last stage of photosynthesis's light-dependent processes involves NADP reductase. It uses the electrons that have gone through the electron transport chain to catalyze the reduction of NADP⁺ to NADPH.

Because it aids in the transmission of electrons from the electron transport chain to NADP⁺, producing NADPH, this enzyme is found on the stroma side of the thylakoid membrane. In the chloroplast stroma, the NADPH generated during this action is subsequently utilized in the Calvin cycle.

Hence, the correct answer is option 2) the Stroma side of the thylakoid membrane

Q3. The chemiosmotic hypothesis was proposed by

1. Warburg

2. Van Niel

3. Emersona and Arnold

4. Peter mitchell

Correct answer: 4) Peter Mitchell

Explanation:

Peter Mitchell first put forth the chemiosmotic concept in 1961. He described how ATP, the energy required for numerous functions, is produced by cells. His theory states that protons (H+) are moved across a membrane using energy, which causes a variation in their concentration. Energy is stored in this difference, also known as the proton gradient. After passing back through an enzyme known as ATP synthase, the protons use this energy to convert ADP and phosphate into ATP. For cells to produce energy during respiration and photosynthesis, this mechanism is crucial. For his efforts, Peter Mitchell was awarded the 1978 Nobel Prize in Chemistry.

Hence, the correct answer is option 4)Peter Mitchell.

Also Read:

• MCQs on Chemiosmotic Hypothesis

• CAM Plants

• Photosynthetic Pigments