electron transport system


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Electron transport systemclick for a larger image
Fig. 146 Electron transport system . Aerobic respiration.
Electron transport systemclick for a larger image
Fig. 145 Electron transport system . Photosynthesis.
Electron transport systemclick for a larger image
Fig. 144 Electron transport system . The role of electron carriers.

electron transport system (ETS)

a series of biochemical steps by which energy is transferred in steps from a higher to a lower level. Each step involves a specific electron carrier which has a particular energy level (or REDOX POTENTIAL), with the carriers organized in a sequence of decreasing energy.

Thus the oxidation of X releases more energy than is required to reduce Y. The released energy can be used to produce ATP, in MITOCHONDRIA and CHLOROPLASTS, probably by a process of chemiosmosis. This mechanism, proposed by P. Mitchell (1920- ), Nobel prize-winner in 1978), involves hydrogen ions (H+) being pumped in or out of the membranes containing the ETS, generating a , proton motive force that enables ATP synthesis from ADP and P.

Electron transport is vital in both PHOTOSYNTHESIS and AEROBIC RESPIRATION:

  1. photosynthesis. Two ET systems are utilized during the LIGHT REACTIONS in the grana of the chloroplasts. One ETS enables the production of ATP by PHOTOPHOSPHORYLATION and the other enables the production of reduced NADP. See Fig. 145 .
  2. aerobic respiration. A molecule of NADH from GLYCOLYSIS or the KREBS CYCLE is passed to the cristae of mitochondria where it is oxidized in the respiratory ETS, the final products being water and three molecules of ATP (= OXIDATIVE PHOSPHORYLATION). See Fig. 146 . The free energy of NADH is approximately 220 kJ. Of this, about 102 kJ are stored in the three ATP molecules (3 × 34 kJ) with the remaining energy being lost as heat, a conversion efficiency of about 46%. FADH enters the ETS at a lower energy level than NADH, yielding only two ATP molecules, not three.
References in periodicals archive ?
Electron transport chain: An electron transport system located in the mitochondria, in which electrons released by NADH are passed on to a series of other molecules that first accept the electrons and then pass them on to the next molecule in the chain.
The worms are paralysed by this form of the dye, we think, because it interferes with some electron transport system that controls movement.
The second experiment was carried out to evaluate the metabolic adaptations to chronic sulphide exposure for 10 days by measuring PK and PEPCK enzyme activities, succinate and alanine content, the adenylate energy charge (AEC), and the activity of the electron transport system (ETS) in whole oysters at above 20 [micro]M.
Using the chalkboard, I introduce the students to the main reactions of glycolysis, the Krebs cycle, and the electron transport system.
Respiratory chain: The electron transport system located in the mitochondria, in which electrons released by NADH are passed on to a series of other molecules that first accept the electrons and then pass them on to the next molecule in the chain.
From there, the energy is transferred to the electron transport system associated with the mitochondrial inner membrane.
Effects of paraquat on mitochondrial electron transport system and catecholamine contents in rat brain.
10], or ubiquinone, a component of the electron transport system and a key player in mitochondrial ATP production.

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