Mitochondria, Power Plants of the Cell
A Simple Explanation of the Cell Organelle Mitochondria
May 6, 2009
The power source of every cell is contained in small organelles called mitochondria. These structures are unique in the cell, different from any other organelle in structure and activity.
What Mitochondria Look Like
Mitochondria are usually rod-shaped structures 0.5–10 micrometers in diameter, but some are round. Different types of cells have different numbers of mitochondria. Some cell types have only one mitochondrion per cell. Others have a few thousand mitochondria.
Mitochondria have two membranes, an inner and outer membrane. The inner membrane has many folds, called cristae, which project into the mitochondrial matrix, the inner compartment of the organelle. The intermembrane space lies between the two membranes.
Mitochondrial DNA and Genetics
Mitochondria have their own DNA, separate from the DNA found in the cell nucleus. The mitochondrial genome in humans and most other animals is a circular strand of DNA containing 37 genes.
This DNA seems to have been derived from bacterial DNA, leading many scientists to believe that mitochondria originated as a bacteria engulfed by primitive cells. Mitochondria also replicate separately from the rest of the cell, splitting in half using binary fission, a method normally employed by bacteria, instead of participating in the mitotic replication that nuclear DNA undergoes.
Unlike nuclear DNA, which is inherited from both parents, mitochondria are passed down almost entirely through the maternal line. Sperm contains very small trace amounts of mitochondria, but they are believed to be mostly destroyed in utero and probably do not contribute to the offspring's mitochondrial genome.
How Mitochondria Power the Cell Using ATP
Mitochondria produce most of the ATP (adenosine triphosphate) in a cell. ATP is the major energy-carrying unit of all cells. This process takes place in the inner membrane and occurs when glucose, pyruvate and NADH are oxidized into ATP. Oxygen is necessary for this process, and is provided via transport channels in the outer membrane and transport molecules that carry the oxygen through the channels into the mitochondria.
The Many Functions of Mitochondria
Supplying energy to the cell is an important job of mitochondria, but it isn't the only one. Some of the other functions of mitochondria are:
- Cell signaling using calcium in many different cell types, including neurons
- Controlling differentiation, the directing of the cell into a certain cell type during development and growth of the cell
- Managing apoptosis by producing proteins that allow programmed cell death to proceed uninhibited.
- Control of the cell cycle by manipulation of cell cycle checkpoints
Sources:
Scheffler, Immo E. Mitochondria. Wiley-Liss. 2007
Ernster, Lars and Schatz, Gottfried. Mitochondria: A Historical Review Journal of Cell Biology. 1981
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