Mitochondria is known as the powerhouse of the cell.
Mitochondria  (sing. mitochondrion) are organelles, or parts of a eukaryote cell. They are in the cytoplasm, not the nucleus..
They make most of the cell's supply of adenosine triphosphate (ATP), a molecule that cells use as a source of energy. Their main job is to convert energy. They oxidise glucose to provide energy for the cell. The process makes ATP, and is called cellular respiration. This means mitochondria are known as "the powerhouse of the cell".
In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signalling, cellular differentiation, cell death, as well as the control of the cell division cycle and cell growth.
A mitochondrion contains two membranes. These are made of phospholipid double layers and proteins. The two membranes have different properties. Because of this double-membraned organization, there are five distinct compartments within the mitochondrion. They are:
the outer mitochondrial membrane,
the intermembrane space (the space between the outer and inner membranes),
the inner mitochondrial membrane,
the cristae space (formed by infoldings of the inner membrane), and
the matrix (space within the inner membrane). Mitochondria are small, spherical or cylindrical organelles. Generally a mitochondrion is 2.8 microns long and about 0.5 microns wide. it is about 150 times smaller than the nucleus. There are about 100-150 mitochondria in each cell.
The mitochondria's main role in the cell is to take glucose and use the energy stored in its chemical bonds to make ATP in a process called cellular respiration. There are 3 main steps to this process: glycolysis, the citric acid cycle or Krebs cycle, and ATP Synthesis. This ATP is released from the mitochondrion, and broken down by the other organelles of the cell to power their own functions..
It is thought that mitochondria were once independent bacteria, and became part of the eukaryotic cells by being engulfed, a process called endosymbiosis.
Most of a cell's DNA is in the cell nucleus, but the mitochondrion has its own independent genome. Also, its DNA shows substantial similarity to bacterial genomes.
The shorthand for mitochondrial DNA is either mDNA or mtDNA. Both have been used by researchers.