Chemiosmosis – this is really important!

The earliest cells, prokaryotes living in an early Earth devoid of free oxygen, used various alternative electron acceptors to carry on anaerobic cellular respiration. After cyanobacteria invented oxygenic photosynthesis and pumped oxygen gas into the oceans and atmosphere, bacteria that adapted their electron transport chains to exploit oxygen as the terminal electron acceptor gained higher energy yield and thus a competitive advantage. One line of aerobic bacteria took up an endosymbiotic relationship within a larger host cell, providing ATP in exchange for organic molecules. The endosymbiont was the evolutionary ancestor of mitochondria. This endosymbiosis must have occurred in the ancestor of all eukaryotes, because all existing eukaryotes have mitochondria (Martin and Mentel, 2010). The evidence for the endosymbiont origin of mitochondria can be found in:

This would become the foundation for what would eventually become the Chemiosmotic theory.

Oxidative phosphorylation uses the energy from a membrane proton gradient to power ATP synthesis from ADP and inorganic phosphate . Image from Wikimedia Commons

Chemiosmotic theory and ATP synthesis | The Biochem …

c. Chemiosmosis

proposed the chemiosmotic hypothesis in 1961. The theory suggests essentially that most synthesis in cells come from the gradient across the inner membranes of by using the energy of and formed from the breaking down of energy rich molecules such as .

Chemiosmotic theory - SlideShare

The of generate energy by chemiosmosis. Chlorophyll loses an electron when energized by light. This electron travels down a ending on the high energy molecule . The generated across the membrane drives the production of ATP by . This process is known as .

The Chemiosmotic theory can explain several key observations ..

In most cases the proton motive force is generated by an electron transport chain which acts as both an electron and proton pump, pumping electrons in opposite directions, creating a separation of charge. In the mitochondria, free energy released from the electron transport chain is used to move protons from the mitochondrial matrix to the intermembrane space of the mitochondrion. Moving the protons to the outer parts of the mitochondrion creates a higher concentration of positively charged particles, resulting in a slightly positive, and slightly negative side (then electrical potential gradient is about -200 mV (inside negative). This charge difference results in an electrochemical gradient. This gradient is composed of both the pH gradient and the electrical gradient. The pH gradient is a result of the H+ ion concentration difference. Together the electrochemical gradient of protons is both a concentration and charge difference and is often called the proton motive force (PMF). In mitochondria the PMF is almost entirely made up of the electrical component but in chloroplasts the PMF is made up mostly of the pH gradient. In either case the PMF needs to be about 50 kJ/mol for the ATP synthase to be able to make ATP.

Stoichiometry of O2 consumption and ATP synthesis

and also can use chemiosmosis to generate ATP. , , and create energy by a process called . These bacteria use the energy of light to create a proton gradient using a photosynthetic . Non-photosynthetic bacteria such as E. coli also contain .

Chemiosmotic theory - definition of Chemiosmotic theory …

In all cells, chemiosmosis involves the proton-motive force (PMF) in some step. This can be described as the storing of energy as a combination of a proton and voltage gradient across a membrane. The chemical potential energy refers to the difference in concentration of the protons and the electrical potential energy as a consequence of the charge separation (when the protons move without a counter-ion).