Structure of Mitochondrial DNA

These scientific biological terms are not easy to understand, unless one is from a science background. Hence, before knowing mitochondrial DNA, one should know the terms like, mitochondria and DNA.

Understanding DNA
Deoxyribonucleic acid (DNA) contains the genetic information, used in the development and functioning of living organisms. It is often called as a blueprint, since it contains the genetic information, from which the components of cell, like proteins and RNA can be constructed. Genes are DNA segments, that carry genetic information. They govern the physical traits of human body like, eye color, hair color, bone thickness, build, etc.

Understanding Mitochondria
Mitochondria is the plural for Mitochondrion. They are rod-shaped organelles, enclosed in a membrane, that is present in many eukaryotic cells. Eukaryotic cells contain complex structures within the enclosed membranes. Mitochondria are considered as powerhouses of the cell, because they take in nutrients and oxygen, and break them down into ATPs (adenosine triphosphate). This is called cellular respiration.

Mitochondrial DNA
DNA is generally present in chromosomes within the nucleus, but mitochondria too have small amounts of their own DNA called as, mitochondrial DNA. The mitochondrial DNA (mtDNA) is present in cytoplasm of the cell.

Mitochondrial DNA is a double stranded circular molecule, which is inherited from the mother in all multicellular organisms. It is because, during fertilization, all mtDNA comes from oocyte. There are about 2 to 10 transcripts of the mtDNA in each mitochrondion. Compared to chromosomes, it is relatively smaller, and contains the genes in a limited number. Changes in mtDNA can cause maternally inherited diseases, which leads to faster aging process and geriatric disorders.

Mitochondrial DNA Structure
Mitochondrial DNA contains about 16,500 DNA building blocks (base pairs), which represents a very small number compared to the total DNA in cells. The genes are essential for the normal functioning of mitochondria. Out of the 37 genes, 13 are responsible for making enzymes, involved in oxidative phosphorylation, a process that uses oxygen and sugar to produce adenosine triphosphate (ATP). The other 14 genes are responsible for making molecules, called transfer RNA (tRNA) and ribosomal RNA (rRNA). These are known as chemical cousins of DNA, as they help to accumulate amino acids into proteins.

mtDNA contains a host of enzymes, and is localized to the matrix. The proteins involved in the respiration are embedded within the mitochondrial inner membrane. Mitochondria have similar characteristics of plant chloroplasts. The plant chloroplasts contain their own DNA, which enables them to grow and reproduce independently.

In some metazoans, there are about 100 - 10,000 separate copies of mtDNA present per cell. Whereas in mammals, each mtDNA molecule consists of about 16,500 base pairs, which encode the 37 genes; 13 for proteins, 22 for transfer RNA (tRNA) and one each for small and large subunit of rRNA. The pattern is same in metazoans, albeit in some cases, one or more of the 37 genes may be absent, and the mtDNA size may be large. Some plants species have numerous mtDNA (as many as 2,500,000 base pairs per mtDNA molecule) but, these mtDNAs still contain same number of genes.

There are about 20,000 to 25,000 total genes in the human genome, and mitochondrial genes are among them.