Genome and Inheritance

Mitochondria possess their own genome separate from that of the nucleus, which takes the form of a small and compact, circular piece of mitochondrial DNA (mtDNA). This genome is small compared to that of the nucleus, containing 16569 base pairs which code for 37 genes involved predominantly in coding for the components of the citric acid cycle and DNA replication.

Despite a mitochondrion having its own discrete genetic sequence, they are not completely independent of the nuclear genome. Nuclear genes can code for machinery found in the matrix that is used to create mitochondrial proteins as well as that used in the maintenance of mtDNA. All products of the nuclear chromosomes however are synthesised in the cytoplasm and later transported into the mitochondria as complete polypeptides.

There can be several thousand copies of the mtDNA loops within a single cell due to the fact the cell contains large numbers of mitochondria which themselves contain multiple numbers of their genome. This number can vary of course depending on the cells’ location within the body. Cells requiring a larger degree of ATP synthesis will contain more mitochondria in order to meet that demand.

Interestingly, mitochondria are inherited maternally rather than from both mates. The mitochondria present in the sperm are unable to enter the egg and the organelles already present in the egg are

 donated to the embryo. This process can have implications in inherited diseases.

 mtDNA diagram courtesy of wikimedia. This image is in the public domain and thus free of any copyright restrictions.