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ATP Synthesis and Chemiosmosis in Photosynthesis - …
Free-energy change during electron transport Another source of electrons for the transport
chain is FADH2.
FADH adds its electrons to the chain in complex II, at a lower energy level then NADH does.
Although both sources each donate an equivalent number of electrons (2) for oxygen reduction, the electron transport chain provides about 1/3 less energy for ATP synthesis when the electron donor is FADH2 rather than NADH.
The amount of energy released by these redox reactions, and thus the amount of energy available for ATP synthesis, depends on the redox potential of the terminal electron acceptor. Oxygen (O2) has the greatest redox potential, and thus results in the most ATP synthesized. Bacteria and Archaea can use other terminal electron acceptors with lower redox potential when oxygen is not available. This produces less ATP.
According to the current model of ATP synthesis ..
In addition to ATP synthesis, prokaryotic cells can use the proton motive force to supply energy for active transport of molecules across the plasma membrane, and to power the motor complex that rotates the bacterial .
The membrane electron transport chain and chemiosmosis is a strategy for cells to maximize the amount of ATP they can make from the large amounts of free energy available in NADH. The electron transport chain subdivides the oxidation of NADH by O2 to a series of lower energy redox reactions, which are used to pump protons across the membrane. The resulting H+ concentration (pH) gradient across the membrane is a form of stored energy, analogous to an electric battery.
chemiosmotic synthesis of atp in photophosphorylation
We have seen how ATP synthase acts like a proton-powered turbine, and uses the energy released from the down-gradient flow of protons to synthesize ATP. The process of pumping protons across the membrane to generate the proton gradient is called . Chemiosmosis is driven by the flow of electrons down the electron transport chain, a series of protein complexes in the membrane that forms an electron bucket brigade. Each of these protein complexes accepts and passes on electrons down the chain, and pumps a proton across the membrane for each electron it passes on. Ultimately, the last complex in the electron transport chain passes the electrons to molecular oxygen (O2) to make water, in the case of aerobic respiration.
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:
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term:chemiosmosis = the synthesis of atp. Study Sets …
The electron transport chain takes electrons from reduced electron carriers (NADH) and passes them to a terminal electron acceptor (O2), and uses the free energy released to generate a membrane proton gradient. Note that the ATP synthase is not part of the electron transport chain, but is shown here because it uses the proton gradient to power ATP synthesis. The ETC builds up the proton gradient, while the ATP synthase discharges the proton gradient in the process of making ATP.
Bacteria and archaea also can use chemiosmosis to generate ATP
The proton motive force drives protons through a channel in the ATP synthase, and turns the rotor at approx 100 rpm. The turning rotor changes the shape of the cytoplasmic subunits (called the F1 ATPase), which bind ADP and inorganic phosphate and bond them together to form ATP. Each 360 degree turn of the rotor results in synthesis of 3 ATP molecules.
ATP synthesis (chemiosmotic theory) - YouTube
Oxidative phosphorylation synthesizes the bulk of a cell’s ATP during cellular respiration. A , in the form of a large proton concentration difference across the membrane, provides the energy for the membrane-localized (a molecular machine) to make ATP from ADP and inorganic phosphate (Pi). The proton gradient is generated by a series of oxidation-reduction reactions carried out by protein complexes that make up an electron transport chain in the membrane. The term oxidative phosphoryation, then, refers to phosphorylation of ADP to ATP coupled to oxidation-reduction reactions.
Chemiosmosis and ATP Synthase - CCBC Faculty Web
Substrate-level phosphorylation means that a phosphate is transferred to ADP from a high-energy phosphorylated organic compound. We will see in the section on metabolic pathways that a couple of the enzymes in make ATP through substrate-level phosphorylation, as well as an enzyme in the . However, only a small amount of ATP is made this way in cells undergoing respiration.
How are chemiosmosis and ATP synthase related? | …
General terms: Chemiosmosis is an energy coupling-mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work.
In mitochondria, the energy for gradient formation comes from exergonic redox reactions, and the ATP synthesis is the work performed.
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