6.26 Electron Transport Chain

The electron transport chain is located on the inner membrane of the mitochondria, as shown below.

Figure 6.261 The pathways involved in aerobic respiration1

The electron transport chain contains a number of electron carriers. These carriers take the electrons from NADH and FADH2, pass them down the chain of complexes and electron carriers, and ultimately produce ATP. More specifically, the electron transport chain takes the energy from the electrons on NADH and FADH2 to pump protons (H+) into the intermembrane space. This creates a proton gradient between the intermembrane space (high) and the matrix (low) of the mitochondria. ATP synthase uses the energy from this gradient to synthesize ATP. Oxygen is required for this process because it serves as the final electron acceptor, forming water. Collectively this process is known as oxidative phosphorylation. The following figure and animation do a nice job of illustrating how the electron transport chain functions.

Figure 6.262 Location of the electron transport chain in the mitochondria2

Web Link

ETC Animation

2.5 ATP/NADH and 1.5 ATP/FADH2 are produced in the electron transport chain. Some  resources will say 3 ATP/NADH and 2 ATP/FADH2, but these values are generally less accepted now.

For one molecule of glucose, the preceding pathways produce:

Glycolysis:   2 NADH

Transition Reaction:  2 NADH

Citric Acid Cycle:     6 NADH, 2 FADH2

Total 10 NADH, 2 FADH2

Multiply that by the amount of ATP per NADH or FADH2 to yield:

10 NADH  X  2.5 ATP/NADH = 25 ATP

  2 FADH2 X 1.5 ATP/FADH2  =  3 ATP

Total 28 ATP

The first video does a nice job of illustrating and reviewing the electron transport chain. Note that it uses 3 ATP/NADH and 2 ATP/FADH2 so the totals from each cycle are different from those listed above. The second video is a great rap video explaining the steps of glucose oxidation.

Web Links

Video: Electron Transport (1:43)

Video: Oxidate it or Love it/Electron to the Next One (3:23)

References & Links

1. http://en.wikipedia.org/wiki/File:CellRespiration.svg

2. http://en.wikipedia.org/wiki/File:Mitochondrial_electron_transport_chain%E2%80%94Etc4.svg


ETC Animation – http://www.science.smith.edu/departments/Biology/Bio231/etc.html


Electron Transport Chain – http://www.youtube.com/watch?v=1engJR_XWVU&feature=related

Oxidate it or Love it/Electron to the Next One – http://www.youtube.com/watch?v=VCpNk92uswY&feature=response_watch