Electron transport chain

The electron transport chain is a group of special proteins and molecules that move tiny particles called electrons from one place to another. This movement happens through a process where electrons both gain and lose energy at the same time. During this process, other tiny particles called protons are also moved across a barrier inside cells.

The energy created by moving these electrons is very important because it helps make a special kind of energy called ATP. This ATP is like the fuel that powers all the work our cells need to do. In cells that use oxygen, like ours, the electrons finally end up joining with oxygen. But in some other kinds of cells, different molecules can take the place of oxygen to accept these electrons.

In our own bodies, this whole process happens inside tiny parts called mitochondria. The energy from this process helps move protons into a special space inside these mitochondria, creating a kind of energy stored in a gradient. This gradient then powers a tiny machine that makes ATP. In plants and some tiny organisms, a similar process happens using light energy instead, also helping to make ATP.

Mitochondrial electron transport chains

Most cells have tiny power plants called mitochondria. These help make a special energy material called ATP. They do this by using oxygen and parts from food.

Inside mitochondria, tiny particles called electrons move through a special path. This path helps create energy by moving other tiny particles called protons. This moving creates a stream that helps make ATP, the cell's energy currency.

The electron path has several steps, each with its own helper tools. These steps work together to move electrons safely and create the energy needed for the cell to stay alive and work properly.

Prokaryotic electron transport chains

In eukaryotes, a special molecule called NADH gives electrons to a chain of protein groups. These groups move the electrons along and help make energy for the cell. The final electron acceptor in this process is oxygen.

In prokaryotes like bacteria and archaea, things are more complex. They can use many different molecules to give electrons and many different molecules to accept them. Bacteria can use three places to start giving electrons: at a special enzyme, at a group of molecules called quinones, or at a moving carrier called a cytochrome.

Bacteria often use many chains at once, depending on what food they have. A common feature in all these chains is a machine that moves tiny particles called protons across a wall inside the cell, creating a difference that helps make energy. Some bacteria have up to three of these machines, just like in our own cells.

Photosynthesis

Further information: Light-dependent reaction and Photosynthetic reaction center

In oxidative phosphorylation, energy is released when electrons move from a donor like NADH to an acceptor like O₂ through a special path called an electron transport chain. In photophosphorylation, the energy from sunlight helps create a powerful electron donor. This donor can then help make energy-rich molecules and link to making ATP, a key energy source, by moving protons across a membrane using the electron transport chain.

Photosynthetic electron transport chains, similar to those in mitochondria, work like special bacterial systems. They use certain mobile molecules to carry electrons, such as phylloquinone and plastoquinone, as well as water-soluble carriers like cytochromes. These chains also include a proton pump. The proton pump in all photosynthetic chains looks like the one in mitochondrial Complex III. The theory of symbiogenesis suggests that these important parts of cells came from ancient bacteria.