Wellcome Trust Centre For Mitochondrial Research

How do mitochondria convert energy?

The machinery that the mitochondria use to convert energy is called the electron transport chain. Mitochondria convert chemical energy, in the form of a chemical called adenosine triphosphate or ATP for short. ATP is an energy currency that every cell in our body can use. This electron transport chain is made up of 4 complexes which are groups of proteins that work together to carry out their function, the 5th complex is responsible for the final step of  energy conversion. It is found in the inner mitochondrial membrane and parts of the first, third, fourth and fifth complexes are coded for by the mitochondrial DNA. In order for energy to be converted several steps have to occur.


Electrons are particles within an atom that are negatively charged, along with the other particles (protons and neutrons) they make up everything in the universe and they are very important in biology. Electrons are passed between the complexes of the electron transport chain and enable the cells to convert energy. The first complex accepts the electrons that are produced from the degradation of the food we eat. As it passes the electrons to the third complex in the chain protons (positively charged hydrogen atoms) are moved across the inner mitochondrial membrane. At complex three the electrons from complex one are joined by others donated by complex two. Complex three passes these electrons onto complex four and in the process moves more protons across the inner mitochondrial membrane. Within complex four the electrons are joined to oxygen to produce water, alongside one final movement of protons. Since so many protons have now been moved across the membrane the amount of them is higher on one side of the membrane than the other, this creates a gradient. Complex five then uses this gradient to produce ATP. The proton gradient rotates this final complex and with each rotation an ATP is made. For every cycle of the electron transport chain over 30 ATPs are produced, this shows how efficient energy conversion is within the mitochondria.

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Electron Transport Chain


What other roles do mitochondria have?

Mitochondria have many roles in addition to energy conversion they also help to monitor and maintain the environment within our cells at the optimum conditions. Mitochondria are crucial to help preserve this environment and their most valuable contribution to this process is that they take up calcium. Calcium is important within cells as a signalling molecule, but this we mean that similar to flares or a 999 call calcium  alerts the cell that something needs to happen, a process needs to begin and the cell needs to respond to what is happening. This signalling needs to be regulated and so the mitochondria store calcium and release it when it is required. Too much free calcium within the cell would be detrimental to the finely tuned regulation of processes within the cell.