One of the biggest mysteries of cell biology is how mitochondria, an oval energy producing organ has its own DNA (MtDNA) and how they still kept this DNA considering the large size of DNA the cell itself has. Scientists think that mitochondria were once independent single-celled organisms until, more than a billion years ago, they were swallowed by larger cells. Instead of being digested, they settled down and developed a mutually beneficial relationship developed with their hosts that eventually enabled the rise of more complex life, like today’s plants and animals. The double membrane of mitochondria is a proof of this theory and it is also similar to how chloroplast in plant cells was also formed. The transfer of MtDNA is exclusively from mother to offspring (male & Female).
Over the years, the size of the mitochondria has reduced with the Nucleus containing a vast majority of genes of which some regulate the functions of the mitochondria itself. For example, there are 37 mitochondrial genes in humans against the over 20,000 genes in the nucleus. It is believed that over the years, genes have jumped from the mitochondria to the nucleus. That sounds interesting, but if that is true, why has the mitochondria still retained some genes up to now? Since their mutation can cause organelle related diseases and can subsequently lead to the dysfunction of brain, liver heart and other delicate organs?
Analyzing more than 2000 different mitochondrial genomes from animals, plants, fungi, and protists (like amoebas), scientists traced their evolutionary path, creating an algorithm that calculated the probabilities that different genes and combinations of genes would be lost at particular points in time. The study concluded that all the remaining mitochondria genes help in energy production and that a gene is more likely to stick around if it is very important to the energy production complex system.It is more likely that hydrophobic protein encoding genes are made in the mitochondria since they may get stuck in transit if they are made elsewhere other than the mitochondria and have to be transported to the mitochondria. The chemical make up of genes can also tell if they stick around or lost over time. The ability to withstand harsh environmental conditions in the mitochondria is one condition that determines the persistence of a gene
Keeping those genes locally in the mitochondria gives the cell a way to individually control mitochondria because pivotal proteins are created in the mitochondria themselves. That local control means the cell can more quickly and efficiently regulate energy production moment-to-moment in individual mitochondria, instead of having to make sweeping changes to the hundreds or thousands of mitochondria it contains.
In a nutshell, it is like grabbing a fire extinguisher to put out the flames when your car catches fire instead of picking up the phone to call the fire service. That is producing certain proteins in the mitochondria where they are mostly needed helps the cell to better regulate energy production