MITOCHONDRIA

Mitochondria Definition

“Mitochondria are membrane-bound organelles present in the cytoplasm of all eukaryotic cells, that produces adinosine triphosphate (ATP), the main energy molecule used by the cell.”

What is Mitochondria?

Popularly known as the “Powerhouse of the cell,” mitochondria (singular: mitochondrion) are a double-membrane-bound organelle found in most eukaryotic organisms. They are found inside the cytoplasm and essentially functions as the cell’s “digestive system.”

They play a major role in breaking down nutrients and generating energy-rich molecules for the cell. Many of the biochemical reactions involved in cellular respiration take place within the mitochondria. The term ‘mitochondrion’ is derived from the Greek words “mitos” and “chondrion” which means “thread” and “granules-like” respectively. It was first described by a German pathologist named Richard Altmann in the year 1890.

Mitochondria Diagram

The diagram of mitochondria below illustrates several structural features of mitochondria.

Mitochondria diagram explaining the structure of mitochondria

Structure of Mitochondria

• The mitochondrion is a double-membraned, rod-shaped structure found in both plant and animal cell.
• Its size ranges from 0.5 to 1.0 micrometre in diameter.
• The structure comprises an outer membrane, an inner membrane, and a gel-like material called the matrix.
• The outer membrane and the inner membrane are made of proteins and phospholipid layers separated by the intermembrane space.
• The outer membrane covers the surface of the mitochondrion and has a large number of special proteins known as porins.
• It is freely permeable to ions, nutrient molecules, energy molecules like the ADP and ATP molecules.

Cristae

The inner membrane of mitochondria is rather complex in structure. It has many folds that form a layered structure called cristae, and this helps in increasing the surface area inside the organelle. The cristae and the proteins of the inner membrane aids in the production of ATP molecules. The inner membrane is strictly permeable only to oxygen and to ATP molecules. A number of chemical reactions take place within the inner membrane of mitochondria.

Mitochondrial Matrix

The mitochondrial matrix is a viscous fluid that contains a mixture of enzymes and proteins. It also comprises ribosomes, inorganic ions, mitochondrial DNA, nucleotide cofactors, and organic molecules. The enzymes present in the matrix play an important role in the synthesis of ATP molecules.

Function of Mitochondria

The most important function of mitochondria is to produce energy through the process of oxidative phosphorylation. It is also involved in the following process:

1. Regulates the metabolic activity of the cell
2. Promotes the growth of new cells and cell multiplication
3. Helps in detoxifying ammonia in the liver cells
4. Plays an important role in apoptosis or programmed cell death
5. Responsible for building certain parts of the blood and various hormones like testosterone and oestrogen
6. Helps in maintaining an adequate concentration of calcium ions within the compartments of the cell
7. It is also involved in various cellular activities like cellular differentiation, cell signalling, cell senescence, controlling the cell cycle and also in cell growth.

Disorders Associated With Mitochondria

Any irregularity in the way mitochondria functions can directly affect human health, but often, it is difficult to identify because symptoms differ from person to person. Disorders of the mitochondria can be quite severe; in some cases, it can even cause an organ to fail.

Mitochondrial diseases: Alpers Disease, Barth Syndrome, Kearns-Sayre syndrome (KSS)

Frequently Asked Questions

1. What is mitochondria?

Mitochondria is a membrane-bound organelle present in the cytoplasm of all eukaryotic cells. It is responsible for producing Adenosine triphosphate (ATP), the main energy currency of the cell.

2. Why are mitochondria called the powerhouse of the cell?

Mitochondria is the cell organelles that are responsible for producing ATP, the energy currency of the cell.

3. Briefly describe the structure of mitochondria.

Mitochondria is a rod-shaped, double membraned organelle. It is found both in plant cells and animal cells.

4. What are cristae?

The inner membrane of mitochondria has many folds. These folds form a layered structure called cristae.

5. What is a mitochondrial matrix?

A mitochondrial matrix is a viscous fluid containing a mixture of enzymes, ribosomes, inorganic ions, mitochondrial DNA, nucleotide cofactors, and organic molecules.

6. What are the functions of Mitochondria?

Mitochondria’s primary function is to produce energy through the process of oxidative phosphorylation. Besides this, it is responsible for regulating the metabolic activity of the cell. It also promotes cell multiplication and cell growth. Mitochondria also detoxes ammonia in the liver cells. Moreover, it plays an important role in apoptosis or programmed cell death.

7. State a few mitochondrial disorders.

Alpers disease, Barth syndrome, Kearns-Sayre syndrome.