Mitochondria – The Power House of Cell


Mitochondria (singular: mitochondrion) are organelles within eukaryotic cells that produce adenosine triphosphate (ATP), the main energy molecule used by the cell.

For this reason, the mitochondrion is sometimes described as “the powerhouse of the cell”.

Mitochondria are found in all eukaryotes, which are all living things that are not bacteria or archaea.

It is believed that mitochondria developed from when free-living bacteria were included in cells.

Evolution of Mitochondria

Mitochondria are believed to have evolved from free-living bacteria that became into a symbiont relationship with a prokaryotic cell, supplying it energy in return for a safe place to live. It ultimately became an organelle, a specific structure within the cell, the existence of which are utilized to differentiate eukaryotic cells from prokaryotic cells.

This occurred over a long process of millions of years ago, and now the mitochondria inside the cell cannot live individually from it. The idea that mitochondria evolved in this manner is called the endosymbiotic theory.



Evidences for Evolution of Mitochondria

Endosymbiotic theory has multiple kinds of evidence. For example, mitochondria have their own DNA that is separate from the DNA in the cell’s nucleus. It is called mitochondrial DNA or mtDNA, and it is just passed down through females due to the fact that sperm do not have mitochondria.

You got your mtDNA from your mother, and you can just pass it on if you are a woman who has a kid. It is likewise circular, like bacterial DNA. Another kind of evidence is the method new mitochondria are created in the cell. New mitochondria just emerge from binary fission, or splitting, which is the same way that bacteria asexually reproduce. If all of the mitochondria are gotten rid of from a cell, it can’t make new ones due to the fact that there are no existing mitochondria there to divide.

Also, the genome of mitochondria and Rickettsia bacteria (bacteria that can cause spotted fever and typhus) have actually been compared, and the sequence is so comparable that it suggests that mitochondria are closely related to Rickettsia.

The Structure of Mitochondria

Mitochondria are little, typically in between 0.75 and 3 micrometers, and are not visible under the microscope unless they are stained. Unlike other organelles (minuscule organs within the cell), they have two membranes, an outer one and an inner one. Each membrane has different functions. Mitochondria are divided into various compartments or regions, each of which carries out distinct roles.

A few of the significant regions consist of the:


Outer membrane

Small particles can pass freely through the outer membrane. This outer portion consists of proteins called porins, which form channels that allow proteins to cross. The external membrane also hosts a variety of enzymes with a wide array of functions.

Intermembrane area

This is the area between the inner and outer membranes.

Inner membrane

This membrane holds proteins that have several functions. Since there are no porins in the inner membrane, it is impenetrable to a lot of particles. Molecules can just cross the inner membrane in special membrane transporters. The inner membrane is where most ATP is created.

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These are the folds of the inner membrane. They increase the area of the membrane, therefore increasing the area readily available for chemical reactions.


This is the area within the inner membrane. Consisting of numerous enzymes, it is important in the production of ATP. Mitochondrial DNA is housed here.

Variety of Mitochondrion in Different Cells

Various cell types have different numbers of mitochondria. For instance, mature red blood cells have none at all, whereas liver cells can have more than 2,000. Cells with a high need for energy tend to have greater numbers of mitochondria. Around 40 percent of the cytoplasm in heart muscle cells is used up by mitochondria.

Although mitochondria are typically drawn as oval-shaped organelles, they are constantly dividing (fission) and bonding together (fusing). So, in reality, these organelles are linked together in ever-changing networks.


Function of Mitochondria
  1. The most essential function of mitochondria is to produce energy. Mitochondria produce the molecule adenosine triphosphate (ATP), one of the cell’s energy currencies that provide the energy to drive a host of cellular responses and mechanisms.
  2. The simple molecules of nutrition are sent to the mitochondria to be processed and to produce charged particles. These charged particles combine with oxygen and produce ATP particles. This process is known as oxidative phosphorylation.
  3. Mitochondria might also produce heat (brown fat), and collect iron-containing pigments (Heme ferritin), ions of Ca2+ and HPO42— (or phosphate; e.g., osteoblasts of bones or yolk proteins).
  4. Mitochondria help the cells to preserve the appropriate concentration of calcium ions within the compartments of the cell.
  5. The mitochondria also help in constructing certain parts of blood and hormones like testosterone and estrogen.
  6. The liver cell’s mitochondria have enzymes that cleanse ammonia.
  7. The mitochondria likewise play a crucial function in the process of apoptosis or set cell death.
  8. Abnormal death of cells due to the dysfunction of mitochondria can impact the function of an organ.

Mitochondria the powerhouse of cells are self-replicating organelles having their own DNA, ribosomes and synthetic machinery. Their size and number vary depending on the physiological activities of the cell.

Their shape also varies. Under the electron microscope, they appear as vesicles, rods or filaments. On deep studying the structure under the electron microscope, the mitochondria are bounded by two membranes the inner and the outer one.

Inner membrane forms folding called cristae. The inner surface of cristae in the mitochondrial matrix contains small knob-like structures, these are called F1 particles.

The mitochondrial matrix contains enzymes, coenzymes, organic and inorganic salts. These enzymes help in key metabolic processes like Krebs cycle, aerobic respiration and fatty acid metabolism.

Mitochondria – The Powerhouse of Cell MCQs

  • What is the primary function of mitochondria?
    • A) Synthesis of proteins
    • B) Storage of genetic material
    • C) Production of energy (ATP)
    • D) Photosynthesis
  • In which cells are mitochondria typically found?
    • A) Bacteria
    • B) Archaea
    • C) Eukaryotic cells
    • D) Viruses
  • According to the endosymbiotic theory, what is the origin of mitochondria?
    • A) Spontaneous generation
    • B) Evolution from other organelles
    • C) Free-living bacteria entering a symbiotic relationship
    • D) Cellular fusion
  • What type of DNA is present in mitochondria?
    • A) Nuclear DNA
    • B) Circular DNA
    • C) Linear DNA
    • D) RNA
  • How do new mitochondria replicate within a cell?
    • A) Meiosis
    • B) Mitosis
    • C) Binary fission
    • D) Budding
  • What is the function of the outer membrane of mitochondria?
    • A) ATP production
    • B) Control the passage of small particles
    • C) Increase surface area for chemical reactions
    • D) House mitochondrial DNA
  • Where is the majority of ATP produced within the mitochondria?
    • A) Outer membrane
    • B) Intermembrane area
    • C) Inner membrane
    • D) Matrix
  • What is the purpose of cristae in mitochondria?
    • A) DNA storage
    • B) Facilitate membrane transport
    • C) Increase surface area for chemical reactions
    • D) Separate inner and outer membranes
  • Which region of the mitochondria houses mitochondrial DNA?
    • A) Outer membrane
    • B) Intermembrane area
    • C) Inner membrane
    • D) Matrix
  • Why is mitochondrial DNA passed down only through females?
    • A) Male cells lack mitochondria
    • B) Female cells lack nuclear DNA
    • C) Sperm do not contain mitochondria
    • D) Mitochondrial DNA is toxic to male cells
  • How do mitochondria contribute to the regulation of calcium ions in cells?
    • A) By storing excess calcium
    • B) By producing calcium ions
    • C) By helping in apoptosis
    • D) By maintaining the proper concentration
  • Which organelle is closely related to mitochondria based on genetic sequence similarities?
    • A) Golgi apparatus
    • B) Endoplasmic reticulum
    • C) Rickettsia bacteria
    • D) Nucleus
  • What is the characteristic shape of mitochondria?
    • A) Linear
    • B) Circular
    • C) Oval
    • D) Irregular
  • How do cells with high energy demands, like heart muscle cells, differ in mitochondria numbers?
    • A) They have fewer mitochondria
    • B) They have no mitochondria
    • C) They have larger mitochondria
    • D) They have more mitochondria
  • Besides ATP production, what other function is associated with mitochondria?
    • A) Photosynthesis
    • B) Synthesis of proteins
    • C) Heat production
    • D) Storage of genetic material
  • What is the process of mitochondrial replication called?
    • A) Fertilization
    • B) Binary fission
    • C) Meiosis
    • D) Mitosis
  • What happens if all mitochondria are removed from a cell?
    • A) The cell undergoes apoptosis
    • B) The cell can’t produce new mitochondria
    • C) The cell loses its shape
    • D) The cell becomes cancerous
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  1. C) Production of energy (ATP)
  2. C) Eukaryotic cells
  3. C) Free-living bacteria entering a symbiotic relationship
  4. B) Circular DNA
  5. C) Binary fission
  6. B) Control the passage of small particles
  7. C) Inner membrane
  8. C) Increase surface area for chemical reactions
  9. D) Matrix
  10. C) Sperm do not contain mitochondria
  11. C) By helping in apoptosis
  12. C) Rickettsia bacteria
  13. C) Oval
  14. D) They have more mitochondria
  15. C) Heat production
  16. B) Binary fission
  17. B) The cell can’t produce new mitochondria


FAQs on Mitochondria

1. What is the main function of mitochondria?

  • Mitochondria are primarily responsible for producing adenosine triphosphate (ATP), which is the main energy currency used by the cell.

2. Where are mitochondria found in living organisms?

  • Mitochondria are found in all eukaryotic cells, which include all living organisms except bacteria and archaea.

3. How did mitochondria evolve according to the endosymbiotic theory?

  • Mitochondria are believed to have evolved from free-living bacteria that formed a symbiotic relationship with a prokaryotic cell, providing energy in exchange for a safe living environment.

4. What evidence supports the evolution of mitochondria?

  • Evidence includes the presence of mitochondrial DNA (mtDNA) separate from nuclear DNA, the circular nature of mtDNA similar to bacterial DNA, and the process of new mitochondria formation through binary fission.

5. What are the structural components of mitochondria?

  • Mitochondria have an outer membrane, intermembrane area, inner membrane, cristae (folds in the inner membrane), and a matrix (innermost compartment containing enzymes and mitochondrial DNA).
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6. How do small particles move through the outer membrane of mitochondria?

  • Small particles can pass freely through the outer membrane, which contains proteins called porins forming channels for particle passage.

7. What is the role of the intermembrane area in mitochondria?

  • The intermembrane area is the space between the inner and outer membranes, contributing to the compartmentalization of mitochondrial functions.

8. Where is ATP primarily produced within the mitochondria?

  • ATP is primarily produced in the inner membrane of mitochondria, where most of the enzymes involved in ATP synthesis are located.

9. How do mitochondria vary in different cell types?

  • Different cell types have varying numbers of mitochondria; for example, mature red blood cells have none, while liver cells can have over 2,000.

10. Besides energy production, what other functions are associated with mitochondria?

  • Mitochondria are involved in heat production, storage of iron-containing pigments, regulation of calcium ion concentration, blood component construction, hormone synthesis, and apoptosis.

11. Can abnormal mitochondrial function affect organ function?

  • Yes, abnormal mitochondrial function leading to the abnormal death of cells (apoptosis) can impact the function of an organ.

12. How are mitochondria depicted in terms of shape, and why is this representation dynamic?

  • Mitochondria are often depicted as oval-shaped organelles. However, their actual shape is dynamic as they are constantly dividing (fission) and bonding together (fusing) in ever-changing networks.

13. What is the significance of mitochondrial DNA being passed down only through females?

  • Mitochondrial DNA is passed down through females because sperm do not contain mitochondria, making maternal inheritance the sole route for passing on mitochondrial DNA.

Summary: Mitochondria – The Powerhouse of Cell Tutorial

The tutorial on mitochondria delves into the vital role these organelles play in eukaryotic cells. Serving as the primary producers of adenosine triphosphate (ATP), mitochondria are aptly described as “the powerhouse of the cell.” The journey of mitochondria is traced through evolution, highlighting the endosymbiotic theory, where they evolved from free-living bacteria into symbiotic relationships with prokaryotic cells.

The evidence supporting mitochondrial evolution includes their distinct DNA (mtDNA), circular in nature like bacterial DNA, and the process of binary fission for new mitochondria formation. Structural insights reveal the intricacies of mitochondria, with two membranes, distinct compartments, and crucial regions such as the outer membrane, intermembrane area, inner membrane, cristae, and matrix.

Mitochondria exhibit diversity in different cell types, with varying numbers based on energy demands. Despite the typical depiction of oval-shaped organelles, mitochondria are dynamic, constantly undergoing fission and fusion, forming ever-changing networks.

The tutorial underscores the multifaceted functions of mitochondria beyond ATP production. These include heat generation, iron pigment accumulation, calcium ion regulation, involvement in blood and hormone synthesis, ammonia cleansing in liver cells, and a pivotal role in apoptosis. Dysfunctional mitochondria can impact cellular health, highlighting their significance in maintaining overall organ function.