Chemiosmosis - Definition, Function and Examples | Biology Dictionary
ATP synthase (also known as FoF1-ATP synthase) is a multisubunit integral membrane protein that produce ATP from ADP and P i using the energy of. Chemiosmosis is the movement of ions across a selectively permeable As protons move through ATP synthase, ADP is turned into ATP. The Chemiosmosis Theory and the Generation of ATP by ATP Synthase charge; the fluid on the opposite side of the membrane is left with a negative charge.
This images shows, very generally, ions moving from high to low concentration during chemiosmosis. The most common method involving chemiosmosis in the production of ATP is cellular respiration in the mitochondria, the process of which is discussed above.
All eukaryotic organisms have mitochondria, so chemiosmosis is involved in ATP production through cellular respiration in the vast majority of different types of organisms, from animals to plants to fungi to protists.
7.4B: Chemiosmosis and Oxidative Phosphorylation
However, even though archaea and bacteria do not have mitochondria, they also use chemiosmosis to produce ATP through photophosphorylation. Plants produce ATP during photosynthesis in the chloroplast in addition to the ATP they generate through cellular respiration in mitochondria.
The process is again similar: Some bacteria, such as cyanobacteria, also use photosynthesis. The similarities between these ATP production methods are more than just coincidence; both mitochondria and chloroplasts are thought to have evolved from free-living bacteria. This theory is called the endosymbiotic theory. This theory hypothesizes that that had symbiotic relationships with other cells, aiding them by producing energy in return for a place to live inside the cell.
The electrons flow through the electron transport chain, causing protons to be pumped from the matrix to the intermembrane space.
Eventually, the electrons are passed to oxygen, which combines with protons to form water. The proton gradient generated by proton pumping during the electron transport chain is a stored form of energy. When protons flow back down their concentration gradient from the intermembrane space to the matrixtheir only route is through ATP synthase, an enzyme embedded in the inner mitochondrial membrane.
Image modified from " Oxidative phosphorylation: This process, in which energy from a proton gradient is used to make ATP, is called chemiosmosis.
- Oxidative phosphorylation
- What is the relationship between chemiosmosis and ATP sythesis?
More broadly, chemiosmosis can refer to any process in which energy stored in a proton gradient is used to do work. For instance, chemiosmosis is also involved in the light reactions of photosynthesis. What would happen to the energy stored in the proton gradient if it weren't used to synthesize ATP or do other cellular work?
It would be released as heat, and interestingly enough, some types of cells deliberately use the proton gradient for heat generation rather than ATP synthesis. In chemiosmotic theory transmembrane ATP synthases are very important. They convert energy of spontaneous flow of protons through them into chemical energy of ATP bonds. Hence researchers created the term proton-motive force PMFderived from the electrochemical gradient mentioned earlier.
It can be described as the measure of the potential energy stored as a combination of proton and voltage electrical potential gradients across a membrane.
In most cases the proton-motive force is generated by an electron transport chain which acts as a proton pump, using the Gibbs free energy of redox reactions to pump protons hydrogen ions out across the membrane, separating the charge across the membrane.
The relationship between ATP synthase and Chemiosmosis
In mitochondria, energy released by the electron transport chain is used to move protons from the mitochondrial matrix N side to the stroma P side. Moving the protons out of the mitochondrion creates a lower concentration of positively charged protons inside it, resulting in excess negative charge on the inside of the membrane. The electrical potential gradient is about mV negative inside N. These gradients - charge difference and the proton concentration difference both create a combined electrochemical gradient across the membrane, often expressed as the proton-motive force PMF.