8.5.4. Mitochondria

Mitochondria (sing.: mitochondrion), unless specifically stained, are not easily visible under the microscope. The number of mitochondria per cell is variable depending on the physiological activity of the cells.

Mitochondria are often referred to as the 'powerhouses' of the cell because they produce the energy that the cell needs to operate. However, without special staining techniques, you can't see them under a regular microscope. The number of mitochondria in each cell depends on how active that cell is; for instance, muscles cells have more mitochondria than skin cells because they need more energy.

Imagine a factory (the cell) that operates machines (the mitochondria) to produce products (energy). If the factory is running continuously (active cell), it needs more machines to keep up with production, so it would have many more machines compared to a factory that occasionally makes products (less active cell).

Typically it is sausage-shaped or cylindrical having a diameter of 0.2-1.0µm (average 0.5µm) and length 1.0-4.1µm. Each mitochondrion is a double membrane-bound structure with the outer membrane and the inner membrane dividing its lumen distinctly into two aqueous compartments, i.e., the outer compartment and the inner compartment. The inner compartment is filled with a dense homogeneous substance called the matrix.

Mitochondria have a specific shape, typically being sausage or cylindrical, and they are quite small, ranging in size. They consist of two membranes: an outer membrane that encases the entire structure and an inner membrane that is folded into structures called cristae. These cristae increase the surface area for energy production. Inside the inner membrane is a fluid called the matrix, where some important chemical reactions take place.

Think of a battery (mitochondrion) that has an outer casing (outer membrane) to protect it and an inner section that is filled with chemical substances (matrix). The inner part has folds (cristae) to maximize space and store more chemicals, ensuring the battery can generate as much power (energy) as possible.

Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called ‘power houses’ of the cell. The matrix also possesses single circular DNA molecule, a few RNA molecules, ribosomes (70S) and the components required for the synthesis of proteins. The mitochondria divide by fission.

The primary role of mitochondria is to carry out aerobic respiration, which is how cells produce energy in the form of ATP (adenosine triphosphate). This process requires oxygen and is essential for most cells. Interestingly, mitochondria have their own DNA and ribosomes, meaning they can produce some of their own proteins. They replicate through a process called fission, similar to how bacteria divide.

Consider mitochondria like the power plants of a city (the cell) that convert energy sources (food and oxygen) into electricity (ATP) that powers everything. Just like power plants may have backup systems or sources of energy stored on-site (like fuel), mitochondria have their own materials to generate energy efficiently.

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