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Topic: Proton gradient


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  Lecture 11. The proton circuit: coupling through the proton gradient
In the steady state, the electron transport chain is inhibited by feed-back from the proton gradient it generates.
In the absence of reactions to use the proton gradient, the rate of electron transfer is slower by a factor of ~10 than in the presence of ADP + phosphate, or an uncoupler (the RC ratio is usually ~10, though the value depends on substrate).
The residual electron transfer is determined by the rate at which protons leak back across the membrane through non-specific pathways, or the rate at which the various proton pumps slip the "clutches" which couple their mechanisms to the gradient.
www.life.uiuc.edu /crofts/bioph354/lect11.html   (1591 words)

  
 The Frasch Lab
Some of the energy initially captured by the photosynthetic light reactions is used to power the vectorial movement of protons from the stroma to the thylakoid lumen, thereby forming a transmembrane proton gradient (3).
of decay of the trans-membrane proton gradient is ~1 sec).
Protons move to the stroma in response to the energy gradient that is derived from the concentration difference across the membrane (DpH).
www.public.asu.edu /~frasch   (1614 words)

  
 1   (Site not responding. Last check: 2007-10-29)
To test whether a proton gradient is sufficient for ATP synthesis one could artificially establish a proton gradient across the relevant membrane (in the absence of reduced compounds or light the organism may use to establish its own proton gradient) and testing for ATP synthesis.
Complex IV contributes to the gradient as protons are absorbed from the inter-membrane space as oxygen is reduced and water is formed.
In the process a quinone ferries protons from the cytoplasmic side of the membrane to the extracellular side of the membrane, thus establishing the proton gradient.
www.towson.edu /~wimmers/MembraneTest2AK.htm   (2068 words)

  
 ATP Production: An Introduction   (Site not responding. Last check: 2007-10-29)
The electron transport chain generates a proton gradient by transporting protons from the mitochondrial matrix to the intermembranal space.
Proton translocation is based on spatial organization of the electron transport chain in the membrane.
The proton gradient becomes greater than normal and yet the potential energy of the gradient cannot be tapped to produce ATP.
home.earthlink.net /~dayvdanls/CampOLs/RespETS.html   (1042 words)

  
 Directional Proton Transport   (Site not responding. Last check: 2007-10-29)
A common motif, however, is the conversion of acquired energy into a proton gradient that is then used to do useful work [27], such as the synthesis of ``high energy'' compounds.
After the proton has been tranferred to the protocellular interior, PS must be reconstituted by a proton from the exterior if the proton gradient is to be maintained.
This coupling of a conformational shift with a hydrogen-bonded chain of proton acceptors to generate irreversibly a transmembrane proton gradient is thought to be used by bacteriorhodopsin [33].
exobiology.arc.nasa.gov /ssx/biomod/1996_pac_symp_biocomp/node5.html   (1274 words)

  
 Biological Oxidations, Oxidative Phosphorylation
These protons are returned to the matrix of the mitochondrion, down their concentration gradient, by passing through ATP synthase coupling electron flow and proton pumping to ATP synthesis.
The energy of the gradient is used to drive ATP synthesis as the protons are transported back down their thermodynamic gradient into the mitochondrion.
Uncoupling agents act as lipophilic weak acids, associating with protons on the exterior of mitochondria, passing through the membrane with the bound proton, and dissociating the proton on the interior of the mitochondrion.
web.indstate.edu /thcme/mwking/oxidative-phosphorylation.html   (3279 words)

  
 [No title]
To investigate the binding sequence of the proton and glutamate to the transporter, the maximum currents (Imax) at saturating glutamate concentrations were compared in a pH range between 6.0 and 10.0.
The proton channel function of gp91phox is still debated, although patch clamp studies in activated phagocytes confirmed the close coupling between H+ channels and the NADPH oxidase (9, 13).
To yield a stronger proton gradient, the proteoliposomes were loaded with 0.5M NH4Cl; diffusion of NH3 out of the liposome leaves protons inside and generates a proton gradient.
www.lycos.com /info/proton.html   (703 words)

  
 untitled
The energy released as the gradient dissapates is used to phosphorylate ADP to ATP (catalysed by ATP synthase).
Proton pumping is not 100% efficient and some free energy is lost as heat during every step.
DNP is protonated while it is in the inner mitochondrial space (since the pH is relatively low due to the high proton conc.) It diffuses across the inner membrane into the matrix where the proton is released (since the pH is higher).
www.dentistry.leeds.ac.uk /biochem/lecture/etran/etran.htm   (1297 words)

  
 studies
Even if there is no proton gradient one beta subunit will be in the T form with bound ATP, which forms spontaneously even in the absence of a proton gradient.
The role of the gradient is to cause the release of bound ATP, not to cause its synthesis.
Because some energy stored in the gradient is always lost as heat or exploited for processes other than ATP synthesis, there is not a one to one correspondence between number of protons translocated by the ETS and number of protons entering the matrix through ATP synthase.
www.ruf.rice.edu /~bioslabs/studies/mitochondria/oxphos.html   (719 words)

  
 I. Overview of Aerobic Metabolism.
Protons are pumped out of the mitochondrial matrix and into the cytosol, producing a pH gradient of 1.5 pH units and a 140 millivolt electrostatic potential difference across the inner membrane.
As a consequence of proton export, the pH of the mitochondrial matrix in actively respiring tissue is 1.4 units higher than the pH of the cytosol.
Both its protonated and deprotonated forms are partially soluble in the hydrocarbon core of the inner mitochondrial membrane.
cmgm.stanford.edu /biochem200/am_syl.html   (5651 words)

  
 BioCarta - Charting Pathways of Life
The inner mitochondrial membrane is impermeable to protons on its own, so the energy of the proton gradient is stable, waiting to be recaptured.
This enzyme allows protons to flow back down their concentration gradient across the membrane, and in the process uses the energy of the gradient to drive ATP synthesis.
The movement of the electrons through electron transport, the proton gradient and ATP synthesis are all coupled processes that require each other to occur.
www.biocarta.com /pathfiles/h_etcPathway.asp   (652 words)

  
 Alternative Respiration   (Site not responding. Last check: 2007-10-29)
One proton is transported by Complex I to the inter membrane space, while two electrons are transported within the inner membrane by the ubiquinone.
Both pathways transfer a proton or protons to the inter membrane space, they transfer a couple of electrons and consume oxygen to yield water.
The difference is that the cytochrome pathway transports two additional protons from the matrix to the inter membrane space, and therefore it enables a greater proton gradient for the same effort.
www.tau.ac.il /~ecology/virtau/2-elitsur/ey.htm   (2113 words)

  
 Botany online: Membranes and Transport - Active Transport
As a consequence of the respiratory chain and of photosynthesis are protons channelled out of the mitochondrial matrix and the thylacoids of the chloroplasts, respectively.
A proton is transported into a compartment and the energy for the transport is supplied by the simultaneous transport of an anion or a substrate molecule in the same direction.
In other words: an electrochemical gradient is used as a source of energy for the active transport of molecules and ions through the membrane.
www.biologie.uni-hamburg.de /b-online/e22/22d.htm   (1230 words)

  
  February 23, 1995
Chemiosmotic theory: a proton gradient serves as the energy reserve that drives ATP formation.
What is important, however, is that the cascade of electron transfers is accompanied by the development of a proton gradient across the inner membrane.
Once, however, the handles are exposed to a proton gradient, the negatively charged groups are protonated and other neutral groups are also protonated.
www.uky.edu /Classes/BCH/401/Watt/Chapter18/chapter18.htm   (616 words)

  
 Cell Biology
That is, the negative free energy of proton movement is coupled to the positive free energy of ATP formation.
The greater the gradient, the greater the negative free energy of a proton's moving through the thylakoid membrane.
Thus it may reduce the amount of protons being pumped in the presence of light, and thus reduce the amount of ATP synthesized in the presence of light, though the reduction is probably negligible under the conditions of the experiment.
www.lclark.edu /~reiness/cellbio/keys/key12000.htm   (2207 words)

  
 A Proton Gradient Powers the Synthesis of ATP
Thus, the role of the proton gradient is not to form ATP but to release it from the synthase.
The entry of protons into the cytosolic half-channel is further facilitated by the membrane potential of +0.14 V (positive on the cytoplasmic side), which increases the concentration of protons near the mouth of the cytosolic half-channel.
Such a rotation moves the newly protonated aspartic acid residue into contact with the membrane, moves the charged aspartate residue from contact with the matrix half-channel to the cytosolic half-channel, and moves a different protonated aspartic acid residue from contact with the membrane to the matrix half-channel.
www.ncbi.nlm.nih.gov /books/bv.fcgi?rid=stryer.section.2528   (2366 words)

  
 LECTURE 16   (Site not responding. Last check: 2007-10-29)
In plants, this energy is derived from the proton electrochem ical gradient with the use of a co-transport system.
A proton pump initiates the process by establishing the gradient (using ATP hydrolysis).
Energy from proton import is available not only because of th e proton gradient is driving protons into the cell, but also because to the elec trical gradient.
www.ucc.uconn.edu /~giardina/LECTUR16.html   (1909 words)

  
 Jeff Goldsmith
Gradient of Proton Density in Saturn's Magnetosphere, Integral Curves
Gradient of Proton Density in Saturn's Magnetosphere, Hedgehog Plot
Gradient of Proton Density in Saturn's Magnetosphere, Baton Plot
www.gg.caltech.edu /~jeff   (1866 words)

  
 Glossary: Oxidative phosphorylation
NADH and FADH2, electron carrier molecules that were "loaded" during the citric acid cycle, are used in an intricate mechanism (involving NADH-Q reductase, cytochrome c oxidase, and cytochrome reductase) to pump H+ across the membrane against a proton gradient.
A large protein complex called ATP synthase is embedded in that membrane and enables protons to pass through in both directions; it generates ATP when the proton moves with (down) the gradient, and it costs ATP to pump a proton against (up) the gradient.
Because protons have already been pumped into the intermembrane space against the gradient, they now can flow back into the mitochondrial matrix via the ATP synthase, generating ATP in the process.
www.greenfacts.org /glossary/mno/oxidative-phosphorylation.htm   (242 words)

  
 BIFC 3521: Lecture
The energy present or stored in the concentration gradient which is set up across a membrane (inside to outside) drives or is captured (converted) in a high energy phosphate bond in ATP (the covalent terminal phosphodiester bond of ATP).The gradient is formed in the mitochondrion in eukaryotes.
Free energy of electron transport is conserved by pumping protons from the mitochondrial matrix to the intermembrane space to form an electrochemical gradient.
The sum result is that heat is generated from the uncoupling of the proton gradient with ATP synthesis.
www.library.csi.cuny.edu /~davis/Biochem_3521/lect19_20/lect19.html   (4443 words)

  
 Electrochemical gradient - Wikipedia, the free encyclopedia
Electrochemical potential is important in electroanalytical chemistry and industrial applications such as batteries and fuel cells.
Membrane transport proteins such as the sodium-potassium pump within the membrane are equivalent to turbines that convert the waters potential energy to other forms of physical or chemical energy, and the ions that pass through the membrane are equivalent to water that is now found at the bottom of the dam.
Proton gradients are also made by bacteria by running ATP synthase in reverse; this is used to drive flagella.
en.wikipedia.org /wiki/Proton_gradient   (1052 words)

  
 Distinguishing between Luminal and Localized Proton Buffering Pools in Thylakoid Membranes -- Ewy and Dilley 122 (2): ...
The extent of proton uptake was measured on the same sets of thylakoids used for determination of the electron transport rates shown in Table II.
Benedetti ED, Garlaschi FM (1977) On the estimation of proton gradient and osmotic volume in chloroplast membranes.
Nishio JN, Whitmarsh J (1993) Dissipation of the proton gradient in intact chlorophasts.
www.plantphysiol.org /cgi/content/full/122/2/583   (6664 words)

  
 [No title]
In chemiosmosis, the proton gradient is used to synthesize ATP.
Because the proton pump moves positive charge (H+) out of the cell, the pump contributes to a voltage known as a membrane potential, a separation of opposite charges across a membrane.
This theory postulates that sugar moves in the phloem by means of a pressure gradient that exists between the source, where sugar is loaded into the sieve tube members, and the sink, where sugar is removed from the phloem.
www.cbu.edu /~esalgado/BIOL112/Campbell/ch36.doc   (2597 words)

  
 Untitled Document   (Site not responding. Last check: 2007-10-29)
The carriers of the electron transport chain pump protons across the crista membrane, forming a gradient, with an excess of protons in the crista space, and an excess of hydroxyl ions in the matrix.
The creation of the proton gradient is seen most simply in complex I, where there is alternation between coenzymes that carry protons and electrons and those that carry only electrons, so that protons are expelled into the crista space, then acquired from water at the matrix face.
Uncouplers are weak acids that transport the protons back into the matrix directly, bypassing the ATP synthetase - the classic example of an uncoupler is 2,4-dinitrophenol, which is water-soluble when deprotonated, but lipid soluble when protonated, so that it will diffuse across the crista membrane down its concentration gradient.
www.ucl.ac.uk /~ucbcdab/oxphos/proton.htm   (324 words)

  
 Proton pump - Wikipedia, the free encyclopedia
For example, the translocation of protons by cytochrome c oxidase is powered by reducing equivalents provided by reduced cytochrome c.
ATP synthase of mitochondria and the CF ligase of chloroplasts, in contrast, usually conduct protons from high to low concentration across the membrane while drawing energy from this flow to synthesize ATP.
To allow the passage of protons a proton channel temporarily opens in the inner membrane.
en.wikipedia.org /wiki/Proton_pump   (396 words)

  
 Using Light Energy to Generate Transmembrane Proton Gradients
The energy stored in the resulting transmembrane charge-separated state is used to pump protons across the membrane, generating a proton gradient, or proton motive force.
The bilayer is spanned by triad artificial reaction centers that undergo photoinduced electron transfer to generate a transmembrane charge-separated state.
A shuttle quinone Qs uses this charge separation to transport protons across the membrane, establishing a proton gradient.
photoscience.la.asu.edu /photosyn/faculty/gust/Liposome.htm   (259 words)

  
 Proton-coupled electron transfer drives the proton pump of cytochrome c oxidase : Nature   (Site not responding. Last check: 2007-10-29)
Electron transfer in cell respiration is coupled to proton translocation across mitochondrial and bacterial membranes, which is a primary event of biological energy transduction.
The resulting electrochemical proton gradient is used to power energy-requiring reactions, such as ATP synthesis.
On the basis of the kinetics of proton uptake and release on the two aqueous sides of the membrane, it was recently suggested that proton pumping by cytochrome c oxidase is not mechanistically coupled to internal electron transfer
www.nature.com /nature/journal/v440/n7085/abs/nature04619.html   (387 words)

  
 Photophosphorylation
The process of creating the Proton gradient resembles that of the electron transport chain of Respiration.
As protons pass through this enzyme ADP and Pi are joined to make ATP.
This Proton gradient can be used to generate ATP chemiosmotically.
bioweb.wku.edu /courses/Biol120/images/Photophosphryl.htm   (293 words)

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