Mitochondria (Singular : Mitochondrion)

Mitochondria – The Powerhouse of the Cell

1. Function and Occurrence
Mitochondria are important cell organelles responsible for aerobic respiration, the process by which cells produce energy (in the form of ATP) using oxygen.
They are absent in prokaryotic cells (like bacteria) and also in red blood corpuscles (RBCs) of mammals.

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2. Shape and Appearance
Mitochondria can have different shapes depending on the cell. They may be:

• Oval

• Spherical

• Spiral strip-like

This variation in shape allows them to fit and function effectively within different types of cells.

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3. Membrane Structure
Mitochondria are double membrane-bound organelles, meaning they have two layers of membrane:

• Outer Membrane:

  • This membrane is permeable to various metabolites (small molecules).

  • This permeability is due to the presence of a protein called Porin (also known as Parson’s particles).

• Inner Membrane:

  • This membrane is selectively permeable, meaning it only allows certain substances to pass through.

  • It plays a crucial role in energy production and electron transport.

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4. Intermembrane Space (Outer Chamber)
The space between the outer and inner membranes is called the outer chamber or intermembrane space. This area is involved in various chemical exchanges.

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5. Cristae – Folded Inner Membrane
The inner membrane is not smooth. It has several finger-like or plate-like folds called cristae.

• These folds increase the surface area for important chemical reactions.

• The cristae contain particles called:

  • Oxysomes (ATP synthase particles)

  • Cytochromes or electron carriers – which help in the electron transport chain, a key step in energy production.

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6. Matrix – Inner Fluid-Filled Chamber
The area enclosed by the inner membrane is called the inner chamber, and it contains a fluid called the matrix.
The matrix contains:

• Coiled circular DNA

• RNA

• 70S ribosomes (like those found in bacteria)

• Lipids

• Enzymes involved in the Krebs cycle and other metabolic pathways

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Conclusion
Mitochondria are essential energy-producing organelles in eukaryotic cells. With their double membrane, cristae, and enzyme-rich matrix, they play a central role in aerobic respiration and ATP generation, making them the powerhouse of the cell.

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Oxysomes – ATP Synthesising Units of Mitochondria

1. Location and Alternate Names
Oxysomes are numerous small particles present on the inner membrane of mitochondria.
They are also known by several other names:

• F1-F0 particles

• Fernandez-Moran particles

• Elementary particles

• Mitochondrial particles

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2. Structure of Oxysomes
Each oxysome has two main parts:

• Head (F1 unit): This part faces the mitochondrial matrix and looks like a lollipop head.

• Stalk or Foot (F0 unit): This part is embedded in the inner membrane of the mitochondria.

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3. Functions of Each Part

• The head (F1) functions as an enzyme called ATP synthase, which is responsible for the formation of ATP (Adenosine Triphosphate – the energy currency of the cell).

• The foot (F0) serves as a proton channel, allowing protons (H⁺ ions) to flow through the inner membrane.

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4. Role in ATP Synthesis
Oxysomes play a crucial role in energy production through the following steps:

• They help in proton pumping, a process where protons are transported across the membrane to create a proton gradient.

• This proton gradient is then used by ATP synthase (in the F1 head) to synthesize ATP from ADP and inorganic phosphate.

• This entire process is part of oxidative phosphorylation during aerobic respiration.

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Conclusion
Oxysomes are essential for energy production in the cell. Located on the inner mitochondrial membrane, they work like tiny machines that use proton flow to generate ATP, the main source of energy for all cellular processes.