Mitochondria are the organelles that release ATP, which is how energy is stored in living things and allows whole organisms, like the human body to function which is pretty impressive for such a microscopic (literally) body. In eukaryotic cells, usually cells that have a nucleus or other organelle such as a plant or animal cell but not bacterial cells, there are about 1,000 mitochondria in each cell and the knowledge we now have in the features and functions of the organelles are due to access to electron microscopy.
The discovery of mitochondria was in 1886 when Richard Altman used dye to identify, although other scientists had claimed to have seen specks in cells before then and Carl Benda, twelve years later named them mitochondria from the Greek mitos meaning thread and khondros/khondrion meaning granule, probably referring to how small the structure was, probably amplified by microscopes not being as developed as they are today with the electron microscope.
The mitochondrion has several features that allow this tiny unit to release the biggest currency in the natural world:
The outer membrane makes the defined oval shape and is semi-permeable to allow substances like oxygen and ATP to diffuse in and out. The inner membrane has many folds and projections that increase surface area, in a similar way that alveoli does in the lungs, called cristae.
Inside the inner membrane, there are enzymes like citrate synthase, ribosomes and the DNA of the mitochondria. The inner membrane is where the chemical reactions take place to release ATP because there is an electron transport chain which couples the electrons with positive hydrogen ions which can be pumped into the space between the membranes (intermembrane) to produce a high proton gradient and because particles diffuse from a high concentration to a low concentration, the protons want to get back into the volume of the inner membrane (the matrix). For this to happen the protons react with enzyme ATP synthase which produces ADP and inorganic phosphate which bond to form ATP, used for things such as body movement and the circulation of blood. Therefore, comparing this unit to nature’s bank is quite fitting as the currency of ATP is something that is released from the mitochondria to then be spent on the body’s needs.
Mitochondria also have their own form of DNA that is used to produce their own proteins and ribonucleic acid that is used to synthesise these proteins.
The organelle has other functions apart from the monster task of supplying the body’s energy:
- It keeps the cell alive but also helps some cells die in order for the rest of the tissue to remain healthy in a system called apoptosis (programmed death) which occurs by proteins securing themselves in the mitochondrial membrane and releasing a different protein called cytochrome which leads to chemical changes that kill the cell.
- Stores calcium ions that are useful for blood clotting, muscle contraction and of course, strong bones.
In the future, mitochondria are rumoured to hold the key to changing cancer treatment, diagnosis and prognosis due to how protein is produced in mitochondria, how it mutates and how it has its own form of DNA. There is also the idea of producing agents and antioxidants that target the mitochondria in order to get rid of damaged mitochondria and also donating mitochondria like blood is donated to combat mitochondrial disease, where the person’s mitochondria are not releasing enough energy as there is currently no treatment for the disease except for the symptoms like seizures being relieved.
What do you think of the future that mitochondria can play in diseases that currently don’t have a cure? Let me know in the comments!
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