Mitochondrion

A mitochondrion (pl. mitochondria) is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. These tiny structures make a special kind of energy called adenosine triphosphate (ATP). Cells use this energy to do their work. Because of this important job, mitochondria are often called the “powerhouse of the cell.” They were first discovered in 1857 by a scientist named Albert von Kölliker and later named by Carl Benda in 1898.

Mitochondria have a special double membrane and contain their own small amount of DNA, which is different from the DNA in the cell’s nucleus. Scientists think that long ago, mitochondria were once free-living bacteria that joined up with early eukaryotic cells. This idea is known as symbiogenesis. Today, mitochondria are found in almost every cell in your body, though some cells, like mature red blood cells, do not have them.

Besides making energy, mitochondria help with many other important jobs in cells, such as sending signals and helping cells grow. The number of mitochondria in a cell can vary — a liver cell can have over 2000, while a red blood cell has none. These tiny structures are very important for keeping all living things alive and healthy.

Structure

Mitochondria can have many different shapes. They have two membranes and five main parts: the outer membrane, the space between the membranes, the inner membrane, the folds of the inner membrane called cristae, and the fluid inside called the matrix.

The inner membrane has folds called cristae, which help it make ATP — the energy coin of the cell. The matrix inside the inner membrane holds special enzymes and DNA that help create this energy.

Function

Mitochondria are tiny parts inside cells that help make energy. They create a special kind of energy called ATP. This energy powers many things that cells do. This process is called respiration. It uses oxygen and sugar to make ATP.

Mitochondria also have other important jobs. They help control how the cell uses its fuel. They store and release calcium. They also help cells talk to each other. Mitochondria are very important for keeping cells healthy and working well.

Organization and distribution

Mitochondria are tiny parts found inside most cells, in animals, plants, and fungi. They often look like small beans but can change shape and move around. Some cells have just one mitochondrion, while others, like liver cells, can have thousands. They help the cell by making energy.

The mitochondria-associated ER membrane (MAM) is an important area where mitochondria connect with another part of the cell called the endoplasmic reticulum (ER). This connection helps the cell manage its energy and materials. The MAM plays a role in handling important cell signals and materials, showing that mitochondria work closely with other parts of the cell.

Main article: Mitochondria associated membranes

Origin and evolution

Main article: Symbiogenesis

Scientists have two main ideas about how mitochondria began. One idea is that they were once simple bacteria that lived inside larger cells, helping them make energy. This is called the endosymbiotic theory. The other idea is that mitochondria formed from a piece of DNA that split off from the cell's nucleus and got surrounded by membranes.

Mitochondria have their own DNA, which is circular like bacterial DNA. They also have small structures called ribosomes that are similar to those in bacteria. These features support the idea that mitochondria came from bacteria. The endosymbiotic theory was popularized by scientist Lynn Margulis, who suggested that mitochondria came from aerobic bacteria that lived inside other cells, helping them make energy more efficiently. This relationship likely developed over a billion years ago.

Some simple organisms today have very small or changed versions of mitochondria, showing that some of their functions are still important.

Mitochondrial genetics

Mitochondria have their own tiny circle of DNA, different from the DNA in the nucleus of the cell. This DNA helps make important parts of the cell’s energy-making machinery. In humans, this mitochondrial DNA is a small loop with just 37 genes that help create energy and do other jobs in the cell.

Scientists study this DNA to learn about family history and how species, including humans, have changed over time. It is passed down only from mothers to their children. Even though it doesn’t change much, scientists have found ways it can mix between cells, helping keep the cell’s energy factories working well.

Dysfunction and disease

Mitochondrial diseases

Main article: Mitochondrial disease

When mitochondria don't work well, it can cause health problems. These problems often affect the brain and muscles. They can also lead to issues like diabetes and problems with hormones. Some diseases happen because of changes in the DNA inside mitochondria. This DNA is passed from mothers to their children. Examples include Kearns-Sayre syndrome and MELAS syndrome.

Mitochondrial problems can also come from changes in the DNA inside the cell's nucleus. This is seen in diseases like Friedreich's ataxia and Wilson's disease. Scientists are studying new treatments, such as mitochondrial replacement therapy, to help prevent these diseases. This area is still new and has many questions.

History

The first observations of structures inside cells that are now known as mitochondria were made in 1857 by Albert von Kolliker. Later, in 1890, Richard Altmann named these structures "bioblasts." The term "mitochondria" was introduced in 1898 by Carl Benda, using words from the Greek language.

Scientists learned more about mitochondria over time. In 1900, Leonor Michaelis found a special dye that could show mitochondria clearly. By the 1940s, researchers discovered that mitochondria help cells create energy. In 1957, mitochondria were nicknamed the "powerhouse of the cell" by Philip Siekevitz. Later, they found that mitochondria have their own tiny structures for making proteins.