Free radical damage to cellsAs discussed in my last blog, mitochondria are little organelles within your cells that are responsible for generating the bulk of your energy needs. I also discussed how, as a natural byproduct of energy generation through the electron transport chain of the mitochondria, some free radicals are produced. Free radicals, or reactive oxygen species(ROS) are molecules that have an unpaired electron in their outer shell. Free radicals are very reactive, and since they are unstable until the unpaired electron finds a partner, they go around to other parts of the cell and try to steal an electron, turning that molecule in to a free radical. It is important to note that this reaction isn't simply with free molecules that are floating around in your cells, free radicals interact with molecules that make up the machinery of your cells. Obviously, if you want your cells to function properly, you want to keep free radicals from getting out of hand.
DNA and free radical damageOne of the problems that you run in to when free radicals get out of hand is the potential for the free radicals to alter the mitochondrial DNA. Every one of our cells has 2 types of DNA, nuclear DNA and mitochondrial DNA. The DNA most of us is familiar with is the nuclear DNA. Both types of DNA contain instructions for building you, but 99.9999999% of those instructions are found in the nuclear DNA. When your cells divide to form new cells, the nuclear DNA splits in to 2 and replicates to form a set of instructions for each cell. If there is damage to the nuclear DNA, this can lead to copy errors which leads to unhealthy, irregular cells.
Certain types of radiation can cause damage to the nuclear DNA. However, the nuclear DNA is surrounded by a membrane that protects it from other parts of the cell, so it probably doesn't get damaged directly by free radicals generated by the electron tranpsort chain in the mitochondria until you are producing huge amounts of them. Since the mitochondrial DNA is within the mitochondrial membrane and is not separated from other parts of the mitochondria by a membrane, free radicals generated by the electron transport chain are free to react with the mitochondrial DNA. While most of the important instructions are contained within the nuclear DNA, the mitochondrial DNA is mostly instructions for proteins contained within the electron transport chain.