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.”

Table of Contents

Read on to explore what is mitochondria, its structure, and functions.

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 function 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.

Also refer: Cell Organelles 

Mitochondria Diagram

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

Mitochondria Diagram

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.


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.

Also Read: Difference between mitochondria and plastids

Functions 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)

Also Read: Eukaryotic Cells

Frequently Asked Questions

1. What are mitochondria?

Mitochondria are 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 are 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 detox 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.

To know more about what is mitochondria, its structure, functions, and a mitochondria diagram, keep visiting BYJU’S website or download BYJU’S app for further reference.

5-Questions' Quiz!


  1. Impressive information its exactly what I was in search of thanks BYJUS you are the best

  2. Thanls for your matter

  3. Can you please explain me what is mitochondrial donation? thanx

    1. Mitochondrial donation is an in-vitro fertilization technique used to treat mitochondrial diseases. The processes involve the extraction of a nuclear DNA from a patient with faulty mitochondria and inserting it into the egg of a healthy donor.

  4. Sachin Jayappanavar

    easily helps to understand the key notes regarding what we need. helps to various students

  5. Thanks for the matter☺️☺️

  6. What is the length and width of the mitochondria in the microscope image?

    1. Most mitochondria have a length of up to 7 µm and a diameter between 0.5 and 1.0 µm.

  7. Thanx for your study material
    And i have a question below
    size of mitochondria is equal to___________

  8. This is the answer to what I was searching for. Thanks a lot to BYJU’s.

  9. This type of explanation I wanted, so I got it, thanks a lot

  10. please can you give reason for why mitochondria have their own dna ??

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