The structure and function of the mitochondrion

Mitochondrion is a vital organelle found in eukaryotic cells. It is often referred to as the “powerhouse of the cell” due to its role in energy production. These small, double-membraned structures are responsible for generating adenosine triphosphate (ATP), which is the primary energy currency of the cell.

Mitochondria have their own DNA, known as mitochondrial DNA (mtDNA), and can replicate independently within the cell. This unique feature suggests that mitochondria may have originated from an ancient symbiotic relationship between an ancestral cell and a prokaryotic organism.

The main function of mitochondria is to carry out cellular respiration, a process that converts nutrients into ATP. This involves a series of complex biochemical reactions, including the citric acid cycle and oxidative phosphorylation. During these processes, electrons are transferred through a series of protein complexes located in the inner membrane of the mitochondrion. This electron transfer generates a proton gradient across the membrane, which is then used to drive ATP synthesis.

Apart from energy production, mitochondria also play a role in other cellular processes. They are involved in calcium signaling, apoptosis (programmed cell death), and regulation of reactive oxygen species (ROS) production. Additionally, mitochondria are known to be dynamic organelles that can change their shape and location within the cell in response to cellular needs.

Mitochondrial dysfunction has been associated with various diseases, including neurodegenerative disorders, cardiovascular diseases, and metabolic disorders. Mutations in mtDNA can lead to mitochondrial diseases, which often affect organs with high energy demands, such as the brain and muscles.

In conclusion, mitochondria are crucial organelles that contribute to the energy metabolism and overall functioning of eukaryotic cells. Their unique structure and functions make them a fascinating area of study in cell biology and have significant implications for human health and disease.


The mitochondrion is a cellular organelle that plays a critical role in energy production and various metabolic processes. It is often referred to as the “powerhouse” of the cell due to its ability to generate adenosine triphosphate (ATP), the primary energy currency of cells. In this article, we will explore the structure and function of the mitochondrion.

1. Structure of the Mitochondrion

1.1 Outer Membrane

The mitochondrion is surrounded by an outer membrane that acts as a protective barrier. It contains porins, which are protein channels that allow the passage of small molecules and ions.

1.2 Inner Membrane

The inner membrane of the mitochondrion is highly folded, forming structures called cristae. These folds increase the surface area available for chemical reactions. The inner membrane also contains proteins involved in the electron transport chain, which is crucial for ATP production.

1.3 Intermembrane Space

The intermembrane space is the region between the outer and inner membranes of the mitochondrion. It contains various enzymes involved in processes such as lipid metabolism and oxidative phosphorylation.

1.4 Matrix

The matrix is the innermost compartment of the mitochondrion. It contains enzymes responsible for the citric acid cycle (also known as the Krebs cycle) and beta-oxidation, which are involved in the breakdown of carbohydrates and fatty acids to produce energy.

2. Function of the Mitochondrion

2.1 ATP Production

One of the primary functions of the mitochondrion is to generate ATP through a process called oxidative phosphorylation. This process occurs in the inner membrane, where electrons are transferred along the electron transport chain, leading to the pumping of protons across the membrane. The resulting proton gradient drives the synthesis of ATP by the enzyme ATP synthase.

2.2 Citric Acid Cycle

The mitochondrion is also involved in the citric acid cycle, a series of chemical reactions that generate high-energy molecules (NADH and FADH2) and produce carbon dioxide as a byproduct. These high-energy molecules are subsequently used in the electron transport chain to produce ATP.

2.3 Beta-Oxidation

In addition to carbohydrate metabolism, the mitochondrion plays a crucial role in fatty acid metabolism. Through a process called beta-oxidation, fatty acids are broken down into acetyl-CoA molecules, which can enter the citric acid cycle to generate ATP.

2.4 Calcium Regulation

Mitochondria also play a role in calcium homeostasis within cells. They can take up calcium ions from the cytoplasm, helping to regulate intracellular calcium levels. Calcium signaling is involved in various cellular processes, including muscle contraction and cell death.


The mitochondrion is a complex organelle with a unique structure that allows it to carry out crucial functions within the cell. It is involved in ATP production through oxidative phosphorylation, the citric acid cycle, and beta-oxidation. Additionally, mitochondria help regulate calcium levels within cells. Understanding the structure and function of mitochondria is essential for comprehending the intricacies of cellular metabolism and energy production.

FAQs: Mitochondrion

1. What is a mitochondrion?

A mitochondrion (plural: mitochondria) is an organelle found in the cytoplasm of most eukaryotic cells. Mitochondria are often referred to as the “powerhouses” of the cell because they are responsible for the production of the majority of the cell’s energy in the form of adenosine triphosphate (ATP).

2. What is the main function of mitochondria?

The primary function of mitochondria is to generate ATP through a process called oxidative phosphorylation. This process involves the breakdown of organic molecules, such as glucose, and the transfer of electrons through a series of electron transport chain complexes, ultimately producing ATP as the final product.

3. What is the structure of a mitochondrion?

Mitochondria have a unique double-membrane structure. The outer membrane is smooth and permeable to small molecules, while the inner membrane is highly folded, forming cristae. The inner membrane contains the enzymes and complexes responsible for oxidative phosphorylation. The space between the inner and outer membranes is called the intermembrane space, and the space inside the inner membrane is called the matrix.

4. How do mitochondria produce ATP?

Mitochondria produce ATP through a process called oxidative phosphorylation, which involves the electron transport chain and the ATP synthase enzyme. Electrons are passed through the electron transport chain, and the energy released is used to pump protons (H+ ions) from the matrix into the intermembrane space, creating a proton gradient. The protons then flow back through the ATP synthase enzyme, driving the production of ATP.

5. Do mitochondria have their own DNA?

Yes, mitochondria have their own circular, double-stranded DNA (mtDNA) that is separate from the nuclear DNA of the cell. Mitochondrial DNA is much smaller than nuclear DNA and encodes a small number of genes, primarily those involved in the electron transport chain and ATP production. This unique feature of mitochondria is evidence that they were once independent, prokaryotic organisms that were engulfed by ancestral eukaryotic cells in a process known as endosymbiosis.

6. What is the significance of mitochondria in the cell?

Mitochondria are essential for cellular function and energy production. They play a crucial role in various cellular processes, such as:

  • ATP production through oxidative phosphorylation
  • Calcium signaling and regulation
  • Steroid hormone synthesis
  • Apoptosis (programmed cell death)

The dysfunction or impairment of mitochondria has been linked to various diseases, including neurodegenerative disorders, diabetes, and cancer.