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2-14 Membranes can help generate energy

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  • In many microorganisms a collection of proteins are involved in generating energy. These proteins move high energy electrons down an electron transport chain and in the process move protons from the inside to the outside of the membrane.
  • This proton gradient can do work by driving other proteins that form ATP, that transport molecules across the membrane, or that move the cell.

Many cells use respiratory processes to obtain their energy. During respiration, organic or inorganic compounds that contain energy are oxidized, releasing electrons to do work. In many microorganisms these electrons find their way to the membrane where they are passed down a series of electron carriers as shown in Figure 2-24. During this operation, protons are transported outside the cell. This creates a gradient of protons across the cell membrane, energizing it, in a fashion similar to charging a battery. The energy of this gradient can then be used to do work directly, a process known as the proton motive force, or can be channeled into a special protein known as ATP synthase. ATP synthase can convert: ADP to ATP, and the ATP can itself do work.

Figure 2-24 Generating the proton motive force

Generating the proton motive force

Membranes are critical in many cells for the generation of usable energy. The cartoon shows the various membrane proteins involved in converting high-energy electrons from photoreceptors into useful energy. They do so by forming a proton gradient across the cell membrane, termed a proton motive force, which is in turn used by other proteins to synthesize ATP. This will be discussed in greater detail in the chapter on metabolism.

The prokaryotic cells performing photosynthesis have membrane systems specific to that process. Light excites electrons found in pigmented proteins in the membrane and the electrons are again passed down through a series of electron carriers. As above, a proton motive force is generated and used to synthesize ATP. The specifics of these systems are discussed in the chapter on metabolism.

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