Mitochondria Function in Humans

Mitochondria are parts of a human cell known as the “energy factories.“  Most human cells, animal cells, and plant cells contain hundreds or even thousands of mitochondria. Some cells, such as muscle cells, contain more mitochondria than those that are less active, like skin cells.

This article describes the structure and function of mitochondria and explains how they affect your body and health.

Mitochondria Quick Facts

All living things are composed of cells. Each cell contains structural components called organelles (almost like mini organs) with specific functions. Mitochondria are a type of organelle.

Location in Body 

Mitochondria are distributed throughout the body. Every tissue and organ in the body is composed of cells, and most cells have many mitochondria. Some cell types have more mitochondria than others due to their energy needs.

The body's cells are enclosed by a cell membrane. They have a nucleus, which holds the genetic material, and a cytoplasm, which holds the organelles. The mitochondria, like other organelles, are located in the cytoplasm.

Basic Structure

Within a cell, each mitochondrion is enclosed by an outer membrane and also has an inner membrane.

The membranes are composed of a combination of fat and protein. Their structure controls the movement of mitochondrial proteins and molecules. Some of these materials are stored between the two membranes, and some are stored within the area that's enclosed by the inner membrane.

The inner membrane has several folds called cristae. The area enclosed by the inner mitochondrial membrane is called the matrix. Within the matrix, each mitochondrion contains particles that aid the production of adenosine triphosphate (ATP). Additionally, there is genetic material in the mitochondrial matrix.

What Do Mitochondria Do?

The main function that occurs inside mitochondria is a chemical reaction that creates ATP, a molecule that the body uses for energy. The mitochondria also have some other roles that are not as well understood as ATP production.

A mitochondrial function that has recently received attention in the context of health is that of cell regeneration, which involves cell death and renewal.

Energy Production

Energy production is the best-recognized and comprehensively studied aspect of mitochondrial function. The structures within this organelle are able to generate ATP through a multistep chemical process.

During this chemical reaction, ATP is produced from glucose (sugar) and oxygen, and carbon dioxide waste is produced. Two major processes of this production (the Krebs cycle and oxidative phosphorylation) take place in the mitochondria.

The ATP that is produced can be stored in the cell. A healthy cell requires efficient production of ATP to meet its energy needs.

Cell Death

Apoptosis is cell degeneration that is controlled. Cell degeneration can occur as part of growth and development or as a natural part of aging. Additionally, cell degeneration can occur as a result of damage or disease.

The mitochondria play a role in programmed cell degeneration and damage-induced degeneration. The mitochondria release enzymes (substances that mediate chemical reactions) that lead to the death of the cell.

Other Functions

The mitochondria are involved in several other functions and can play a role in the initial steps, or may be involved in one or more subsequent steps of the physiological process.

Functions that involve mitochondria include:

• Calcium movement in the cell
• Synthesis of heme (an iron-carrying protein)
• Formation of iron-sulfur clusters, which help in a variety of biological functions

What Happens When Mitochondria Doesn’t Function Like It Should?

There can be many consequences of mitochondrial dysfunction, including low energy and impaired cell regeneration. Several diseases are known to be caused by impaired mitochondrial function.

Examples of mitochondrial diseases include:

• Leigh syndrome: This childhood neurodegenerative disease are inherited due to defects in the mitochondrial DNA. This disease is usually fatal within the first five years of life.
• Mitochondrial myopathy: Symptoms of this condition include weakness, muscle cramps, and muscle atrophy (thinning of the muscles). There are several variants of mitochondrial myopathy, with different severities, age of onset, and inheritance patterns.
• Myoclonus epilepsy with ragged red fibers (MERRF): This condition causes seizures, muscle jerks, muscle weakness, and impaired coordination.

Mitochondrial diseases are diverse, and are estimated to affect 1 in 5,000 live births.

Some mitochondrial diseases are inherited. The hereditary pattern of mitochondrial disease is very complicated.

Hereditary mitochondrial diseases can be passed down due to defects in the nuclear DNA (this is the DNA that contains most of the genetic material of the body), and some are passed down through mitochondrial DNA. One of the features of mitochondrial DNA is that it is inherited maternally, which means that it is inherited specifically from the female genetic parent.

Additionally, many diseases that are not specifically caused by mitochondrial dysfunction may involve impaired action of the mitochondria, even when mitochondrial disease is not the main cause. Examples include cancer, Parkinson’s disease, and Huntington’s disease.

These diseases can cause mitochondrial damage, and damage to the mitochondria can worsen the disease.

Summary 

The mitochondria are abundant throughout the body. These structures are a type of organelle, and multiple mitochondria are found within each cell in humans, animals, and plants.

The mitochondria have many roles, but the most well-understood is that of energy production in the form of ATP. Mitochondrial dysfunction can lead to disease, and it can also be caused by disease.