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.

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.