Questions & Answers

1. What are mitochondria and what is their function?

Mitochondria are tiny structures found in almost every cell in our bodies. They convert the food we eat into the energy we need to survive and grow.

Mitochondria are tiny and contain only 37 genes.

Inside the mitochondria, a chain of chemical reactions takes place that changes the food we have eaten and digested into a form of energy that cells in our body can use. This 'cellular energy' is called ATP (Adenosine Triphosphate).

The whole process is known as The Electron Transport Chain or The Respiratory Chain.

There are a number of complex chemical changes that happen during this production line involving hundreds of proteins, each with its own special job to do.

Scientists split this process into five separate reactions. The first four involve the transfer of electrons along a pathway, and the fifth stage completes the process with the end result being production of ATP energy that our bodies can use.


These different stages in the process are referred to as Complex I, Complex II, Complex III, Complex IV and Complex V.

When any one of these steps is blocked, usually because a genetic defect has prevented the manufacture of a protein required for that step, mitochondrial disease can occur. The body can't function properly because the cell's ability to make energy is reduced or stopped, and metabolic intermediates and toxic bi-products begin to build up.

The energy shortage in the tissues is the major cause of muscle weakness, fatigue and problems in the heart, kidneys, eyes and endocrine system. The build-up of toxic intermediates can be responsible for liver problems, muscle cramps, brain dysfunction or even greater mitochondrial damage. Many times these two types of problems reinforce one another, each making the other worse.

When doctors are diagnosing a patient with a mitochondrial disorder, tests may indicate which part of this process is not working properly and the patient might be described as having a particular complex affected eg. 'Complex I Mitochondrial Disease' indicates that the problem has arisen in the first stage (the first complex) of the Electron Transport Chain.

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