What is the Difference Between Chemiosmosis in Mitochondria and Chloroplast

The key difference between chemiosmosis in mitochondria and chloroplast is that in mitochondrial chemiosmosis, the source of energy is food molecules, while the energy source for chemiosmosis in chloroplast is received by a light source.

Chemiosmosis is the movement of ions from one side of a biological semipermeable membrane to another across an electrochemical gradient. The gradient allows the ions to pass passively with the help of proteins embedded in the membrane. This helps ions to move from an area of higher concentration to an area of lower concentration. This process is similar to osmosis, but it involves ions moving across the membranes through a gradient.

CONTENTS

1. Overview and Key Difference
2. What is Chemiosmosis in Mitochondria
3. What is Chemiosmosis in Chloroplast
4. Similarities – Chemiosmosis in Mitochondria and Chloroplast
5. Chemiosmosis in Mitochondria vs Chloroplast in Tabular Form
6. Summary – Chemiosmosis in Mitochondria vs Chloroplast

What is Chemiosmosis in Mitochondria?

Chemiosmosis in mitochondria is the pumping of protons through special channels in the membranes of mitochondria from the inner membrane to the outer membrane. During this process, the electron carriers, NADH and FADH, donate electrons to the electron transport chain. These electrons make conformational changes in the proteins for them to pump H+ ions across a selectively permeable membrane. Uneven distribution of H+ ions across the membrane causes a difference in concentration and electrochemical gradient. Therefore, positively charged hydrogen ions move and aggregate on one side of the membrane. Many ions move through the nonpolar regions of phospholipid membranes with the aid of ion channels. This causes the hydrogen ions in the matrix to pass through the inner mitochondrial membrane with the help of a membrane protein called ATP synthase. This protein utilizes the potential energy in the hydrogen ion gradient to add a phosphate to ADP, forming ATP.

Chemiosmosis generates the majority of ATP during aerobic glucose catabolism. The production of ATP in mitochondria using chemiosmosis is known as oxidative phosphorylation. At the end of this process, electrons help to reduce oxygen molecules to oxygen ions. Extra electrons on the oxygen interact with H+ ions to form water.

What is Chemiosmosis in Chloroplast?

Chemiosmosis in chloroplasts is the movement of protons for the production of ATP in plants. In chloroplast, chemiosmosis takes place in the thylakoid. Thylakoid harvests light and serves as the location for light reactions during photosynthesis. The light reactions generate ATP by chemiosmosis. The antenna complex of photosystem II receives the photons in sunlight. This excites electrons to a higher energy level. Electrons then transport down through the electron transport chain, pumping protons actively across the thylakoid membrane into the lumen of the thylakoid.

With the help of an enzyme ATP synthase, protons flow down an electrochemical gradient. This generates ATP by phosphorylation of ADP to ATP. These electrons from the first light reaction reach photosystem I and then reach a higher energy level by light energy and are received by an electron acceptor. This reduces NADP+ to NADPH. Oxidation of water, which splits into protons and oxygen, replaces the electrons which are lost from photosystem II. In order to generate one molecule of oxygen, photosystems I and II absorb at least ten photons. Here, four electrons move through the photosystems and generate two NAPDH molecules.

What are the Similarities Difference Between Chemiosmosis in Mitochondria and Chloroplast?

• Chemiosmosis in mitochondria and chloroplast have the same theory – to move ions across a semipermeable membrane down an electrochemical gradient.
• Both use high energy sources for the chemiosmosis process.
• Hydrogen ions or protons diffuse through the membranes.
• Both generate ATP.
• Moreover, both use membrane proteins and enzyme ATP synthase.

What is the Difference Between Chemiosmosis in Mitochondria and Chloroplast?

In mitochondrial chemiosmosis, the source of energy is food molecules, while the energy source for chemiosmosis in the chloroplast is the sunlight. Thus, this is the key difference between chemiosmosis in mitochondria and chloroplast. Moreover, in mitochondria, chemiosmosis occurs across the inner mitochondrial membrane whereas, in the chloroplast, chemiosmosis takes place in the thylakoid lumen. Also, in mitochondria, ATP is generated in the matrix of mitochondria, while in chloroplast, ATP is generated outside the thylakoid.

The below infographic presents the differences between chemiosmosis in mitochondria and chloroplast in tabular form for side by side comparison.

Summary – Chemiosmosis in Mitochondria vs Chloroplast

Chemiosmosis is the movement of ions from one side of the biological semipermeable membrane to another across an electrochemical gradient. Chemiosmosis in mitochondria is the pumping of protons through special channels in the membranes of mitochondria from the inner membrane to the outer membrane. Chemiosmosis in chloroplasts is the movement of protons for the production of ATP in plants. In the chloroplast, chemiosmosis takes place in the thylakoid. Both processes involve generating ATP using energy. In the mitochondria, the energy source is from redox reaction during metabolism of food molecules, while in chloroplast, the energy source is light. So, this summarizes the difference between chemiosmosis in mitochondria and chloroplast.

Reference:

1. “Chemiosmosis.” Biology Articles, Tutorials & Dictionary Online, 21 Dec. 2021.
2.“7.4B: Chemiosmosis and Oxidative Phosphorylation.” Biology LibreTexts, Libretexts, 19 Mar. 2021

Image Courtesy:

1. “Mitochondrial electron transport chain” By User:Rozzychan – http://en.wikipedia.org/wiki/Image:Etc2.png (CC BY-SA 2.5) via Commons Wikimedia
2. “Chemiosmotic proton transfer” By Darekk2 – Own work (CC BY-SA 3.0) via Commons Wikimedia