Definition of electron transport chain

Answer 1

ETCThe Electron Transport Chain or System (ETC/ETS) is a process used in both respiration and photosynthesis that produces energy (ATP) through oxidative (photo)phosphorylation. It begins with an electron-carrying molecule (NADH and FADH2 in respiration and NADPH in photosynthesis) transferring its electrons to an enzyme embedded in a membrane. Through a series of redox reactions, electrons move from one enzyme to another. At each stop, a small amount of energy is released - this is used to make ATP. There is high potential energy in the first steps, but as electrons progress through the chain, free energy is incorporated into ATP as usable chemical energy.

Equally important is the ETC's ability to create a proton gradient. Protons (really hydrogen ions, H+) are released from the electron donors such as NADH. This creates a high concentration of protons on one side of a membrane and a low concentration of protons one the other side. Because the protons "want" to diffuse back across the membrane, they will release energy when crossing. ATP synthase captures this energy to make ATP in a process called chemiosmosis.

The ETC involves many complex molecules - some of which are not fully understood. For more information about the process and function behind the ETC, see the related links below.

Answer 2

in this step the energy carried by electrons is used to synthesize (ATP).

In electron transport chain NADH and FADH2 realese electrons and hydrogen ions. These electrons are taken up by a series of electron carriers. When electrons move through the series of electron carriers they lose electrons and hydrogen ions combine with moleculaer oxygen to form water.

Answer 3

Electron Transport

Introduction:

The majority of the energy conserved during catabolism reactions occurs near the end of the metabolic series of reactions in the electron transport chain. The electron transport or respiratory chain gets its name from the fact electrons are transported to meet up with oxygen from respiration at the end of the chain. The overall electron chain transport reaction is:

2 H+ + 2 e+ + 1/2 O2 ---> H2O + energy

Notice that 2 hydrogen ions, 2 electrons, and an oxygen molecule react to form as a product water with energy released in an exothermic reaction. This relatively straight forward reaction actually requires eight or more steps. The energy released is coupled with the formation of three ATP molecules per every use of the electron transport chain.

Link to a complete animated version of Electron Transport - Brooks-Cole

Link to: Rodney Boyer Animation of Electron Transport

Pre-Initiation of Electron Transport Chain:

The electron transport chain is initiated by the reaction of an organic metabolite (intermediate in metabolic reactions) with the coenzyme NAD+ (nicotinamide adenine dinucleotide). This is an oxidation reaction where 2 hydrogen atoms (or 2 hydrogen ions and 2 electrons) are removed from the organic metabolite. (The organic metabolites are usually from the citric acid cycle and the oxidation of fatty acids--details in following pages.) The reaction can be represented simply where M = any metabolite.

MH2 + NAD+ -----> NADH + H+ + M: + energy

One hydrogen is removed with 2 electrons as a hydride ion (H-) while the other is removed as the positive ion (H+). Usually the metabolite is some type of alcohol which is oxidized to a ketone.

NAD+ is a coenzyme containing the B-vitamin, nicotinamide, shown on a previous page.

The purpose of the other seven steps in the electron transport chain is threefold:

1) to pass along 2H+ ions and 2e- to eventually react with oxygen;

2) to conserve energy by forming three ATP's; and

3) to regenerate the coenzymes back to their original form as oxidizing agents.

Initiation of Electron Transport Chain:

Once the NADH has been made from a metabolite in the citric acid cycle inside of the mitochondria, it interacts with the first complex 1 enzyme, known as NADH reductase. This complex 1 contains a coenzyme flavin mononucleotide (FMN) which is similar to FAD.

The sequence of events is that the NADH, plus another hydrogen ion enter the enzyme complex and pass along the 2 hydrogen ions, ultimately to an interspace in the mitochondria. These hydrogen ions, acting as a pump, are utilized by ATP synthetase to produce an ATP for every two hydrogen ions produced. Three complexes (1, 3, 4) act in this manner to produce 2 hydrogen ions each, and thus will produce 3 ATP for every use of the complete electron transport chain.

In addition, NADH passes along 2 electrons to first FMN, then to an iron-sulfur protein (FeS), and finally to coenzyme Q. The net effect of these reactions are to regenerate coenzyme NAD+. This regeneration of reactants occurs in many of the reactions so that a cycling effect occurs. The NAD+ is ready to react further with metabolites in the citric acid cycle.

Coenzyme Q, which also picks up an additional 2 hydrogen ions to make CoQH2, is soluble in the lipid membrane and can move through the membrane to come into contact with enzyme complex 3.

In summary, the very first enzyme complex in the electron transport chain is coupled with the formation of ATP. The coupled reaction may be written as:

a) MH2 + NAD+ ---> NADH + H+ + M + energy

b) ADP + P + energy ---> ATP + H2O

Electron Transport - Enzyme Complex 3:

Coenzyme QH2 carrying an extra 2 electrons and 2 hydrogen ions now starts a cascade of events through enzyme complex 3, also known as cytochrome reductase bc.

Cytochromes are very similar to the structure of myoglobin or hemoglobin. The significant feature is the heme structure containing the iron ions, initially in the +3 state and changed to the +2 state by the addition of an electron. The CoQH2 (yellow)passes along the 2 electrons first to cytochrome (blue) b1 heme (magenta), then b2 heme , then to an iron-sulfur protein (green), then to cytochrome c1 (red with black heme), and finally to cytochrome c (not shown). Co Q is represented by the inhibitor antimycin (yellow) in the graphic.

In the meantime the 2 hydrogen ions are channeled to the interspace of the mitochondria for ultimate conversion into ATP.

Complex 4: Refer to the middle graphic: Cytochrome c is a small molecule which is also able to move in the lipid membrane layer and diffuses toward cytochrome a complex 4.

Cytochrome c - Chime in new window

At this time it continues the transport of the electrons, and provides the third and final time that 2 hydrogen ions are channeled to the interspace of the mitochondria for ultimate conversion into ATP.

ATP synthetase is also found at numerous locations in the bilayer membrane of the mitochondria. The function of this ATP enzyme is found in an earlier page. Three ATP are producedby the pumping action of the re-entry of the hydrogen ions through the ATP synthetase.

Finally, oxygen has diffused into the cell and the mitochondria for the finally reaction of metabolism. Oxygen atom reacts with the 2 electrons and 2 hydrogens to produce a water molecule.

Answer 4

in electron trasport chain NADH and FADH2 release electron and hydrogen ions. these electron are taken up by a series of electron carriers.when electron move through the series of electron carrier they lose energy,which is used to synthesize ATP molecules .at the end of the chain electron and hydrogen ions combine to form water.

Answer 5

This is the series of complexes in the inner membrane of mitochondria where electron oxidized from food fall down there electronegative concentration gradient and with the energy released from this fall protons are pumped across the membrane from the matrix to the intermembrane space where the protons build up a proton motive force. The electrons are joined with the final electron acceptor oxygen at the end of the chain.

Answer 6

An electron transport chain (ETC) couples a reaction between an electron donor (such as NADH) and an electron acceptor (such as O2

Answer 7

The electron transport chain makes ATP.

Each electron carrier alternates between being reduced and being oxidized.

Answer 8

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