What are Mitochondria? All You Need to Know
Mitochondria play a vital role in the life of eukaryotic cells. Known popularly as the powerhouses of the cell, these rod-shaped organelles generate adenosine triphosphate (ATP), the main energy currency. They also take part in processes like cellular respiration, cell growth, and many other essential activities. Understanding the structure, and function of mitochondria can help you learn this crucial topic in biology.
What are Mitochondria?
Mitochondria are double-membraned, rod-shaped organelles found in the cytoplasm of most eukaryotic cells. The singular term ‘mitochondrion’ comes from Greek words meaning “thread” and “granule.” These organelles were first described by the German pathologist Richard Altmann in 1890.
Key Points
They are present in both plant cells and animal cells.
They are crucial for cellular respiration, differentiation, cell signalling, and controlling the cell cycle.
They have their genetic material (mitochondrial DNA) and ribosomes.
They produce ATP, which powers various biological processes.
Structure of Mitochondria
Matrix
The matrix is the viscous fluid enclosed by the inner membrane.
It contains enzymes for oxidative phosphorylation, ribosomes, mitochondrial DNA, ions, and other molecules.
It plays a key role in the Krebs cycle and in generating molecules that feed into ATP production.
Cristae
Cristae are the folds of the inner membrane that project into the matrix.
These folds greatly increase the surface area, enabling enhanced ATP production during cellular respiration.
Ribosomes
Mitochondrial ribosomes (mitoribosomes) synthesise some of the proteins needed by mitochondria.
They translate specific mRNAs encoded by the mitochondrial DNA.
Inner Membrane
The inner membrane contains several unique transporter proteins.
It is selectively permeable, which means it carefully regulates molecules entering or leaving the mitochondrial matrix.
Outer Membrane
The outer membrane contains proteins called porins, forming channels that allow smaller molecules to pass into the intermembrane space.
It also houses enzymes that help in various metabolic and signalling functions.
Intermembrane Space
This is the region between the inner and outer membranes.
It can be further divided into the intra-cristae space and the lumen, which are separated by narrow openings known as cristae junctions (10 to 40 nm in diameter).
It is important in protein transport, protein modification, and in regulating apoptosis (programmed cell death).
Function of Mitochondria
ATP Production: Mitochondria generate ATP through oxidative phosphorylation, a process that occurs along the inner membrane.
Cellular Respiration: They utilise oxygen to convert nutrients into energy.
Metabolic Activities: Mitochondria are involved in various metabolic pathways, including the Krebs cycle.
Cell Signalling: They help regulate calcium levels and influence signalling cascades that control cell growth.
Apoptosis: Mitochondria release factors that initiate programmed cell death, maintaining tissue health by removing damaged cells.
These roles underscore why these organelles are often called the “powerhouses” of the cell.
Quiz on Mitochondria
Test your understanding with these simple questions:
1. Which membrane of the mitochondria is folded to form cristae?
a) Outer membrane
b) Inner membrane
c) Intermembrane space
d) Matrix
Answer: b) Inner membrane
2. What is the main function of mitochondria?
a) Production of proteins
b) Storage of genetic material
c) ATP production
d) Cell wall formation
Answer: c) ATP production
3. Who first described mitochondria?
a) Gregor Mendel
b) Richard Altmann
c) Louis Pasteur
d) James Watson
Answer: b) Richard Altmann
Related Topics
FAQs on Diagram of Mitochondria: Structure, Labelling and Functions
1. Can mitochondria replicate on their own?
Yes, mitochondria can replicate independently within a cell because they contain their DNA. This form of replication is often referred to as mitochondrial biogenesis.
2. Are mitochondria present in all cells?
They are found in almost all eukaryotic cells, including plant and animal cells. However, some specialised cells (such as red blood cells in mammals) lack mitochondria.
3. What role do mitochondria play in apoptosis?
Mitochondria release certain factors (such as cytochrome c) that trigger the cascade leading to cell death, ensuring the removal of damaged or unwanted cells.
4. How do mitochondrial diseases arise?
Mitochondrial diseases can occur due to mutations in mitochondrial DNA or nuclear DNA that affect mitochondrial function. These often result in reduced ATP production.
5. Why are mitochondria called the ‘powerhouse of the cell’?
They are called the powerhouse of the cell because they produce the majority of the cell’s ATP, which is used as a direct source of energy for various cellular processes.
