Detroit Medical Center - About Mitochondrial medicine - Genetics

Genetics

Genes contain the instructions or blue prints to make proteins that are necessary for cell survival and for cells to carry out their normal functions. Skin cells, for example, make the protein keratin that gives skin its tough yet resilient surface. The genes are located on chromosomes, cellular organelles shaped like small threads that are located within the cell’s nucleus and are composed mainly of DNA. Chromosomes come in pairs, 23 in all, so that each cell contains 46 chromosomes. One chromosome of each pair comes from a person’s mother, while the other comes from their father. Pairs 1 through 22 are called the autosomes and are the same in both men and women. The last pair, however, contains the sex chromosomes. Men have both an X and a Y sex chromosome: an X from their mother, and a Y from their father. In contrast, women have two X chromosomes. The human genome consists of the DNA in a set of 23 chromosomes and encodes approximately 20-25, 000 genes.

Each mitochondrion also has its own chromosome separate from the 23 pairs of chromosomes located within the nucleus of the cell. The mitochondrial chromosome is a small circular DNA that encodes 37 genes not contained within the nuclear genome. Proteins that are made from these genes are located within the mitochondrion, and are necessary for the mitochondrion to function properly. Since the mitochondrion requires several hundred different proteins for its normal function, however, additional mitochondrial proteins are also encoded by the nuclear genome. Mitochondria thus have proteins produced from both the nuclear and the mitochondrial chromosomes. Genetic disorders that alter mitochondrial function can be caused by mutation in one of the 23 pairs of chromosomes located within the nucleus of the cell, or by mutation in the chromosome located within each mitochondrion.