Episode 5 · MAPASGEN · PRO Material
Level: advanced · Topic: mitochondrial biology, inherited disease, reproductive technology
Mitochondria are perhaps the most remarkable structures in the cell. Not because they do anything spectacular, but because their history is a story of symbiosis stretched across one and a half billion years. And it is precisely their vulnerability that has become one of the central challenges in reproductive medicine today.
About 1.5 billion years ago, an ancient cell — the ancestor of all modern eukaryotes — engulfed a bacterium. Normally such stories end in digestion. But this time something went differently: the bacterium was not digested. Instead it remained inside the host cell, producing energy for it in exchange for protection and nutrients.
This event is called endosymbiosis, and it is what made complex multicellular life possible. Without mitochondria, we would have no brain, no heart, no muscles — no organ requiring significant amounts of energy.
Traces of this bacterial origin are still present today. Mitochondria have their own circular DNA — like bacteria. They divide independently of the cell. They have two membranes — an outer (cellular) one and an inner (their own, bacterial) one. And they are sensitive to antibiotics that kill bacteria — precisely because some mechanisms are shared.
A fact that is difficult to absorb: The mitochondria inside your cells are, in the most literal sense, descendants of bacteria captured by another cell one and a half billion years ago. You are not a single organism. You are an ecosystem shaped by evolution. |
The process is called oxidative phosphorylation — and despite the intimidating name, it can be explained through a simple analogy.
Imagine a dam on a river. Water presses against a turbine and generates electricity. In mitochondria, the role of 'water' is played by electrons stripped from nutrient molecules (carbohydrates, fats). They 'flow' along a chain of protein complexes on the inner mitochondrial membrane — the electron transport chain. The energy of this 'current' pumps protons across the membrane, creating an electrochemical gradient — a kind of pressure. This pressure drives the rotation of a protein called ATP synthase, which produces ATP from ADP and phosphate — the universal 'currency' of cellular energy.
On average, a person produces and consumes an amount of ATP roughly equal to their own body weight — every single day. During physical exertion, this figure multiplies many times over.
The mitochondrial genome is small — just 37 genes. But mutations in any one of them can have catastrophic consequences, especially for organs with high energy demands: the brain, heart, muscles, and kidneys.
Mitochondrial diseases are a group of rare inherited conditions united by disruption of energy metabolism. They vary widely in presentation but often include:
The combined prevalence of mitochondrial diseases is approximately 1 in 5,000 — making them one of the most common groups of inherited metabolic disorders. Most are untreatable: we can relieve symptoms but not eliminate the cause.
A note on inheritance: Mitochondrial diseases caused by mutations in mtDNA are passed exclusively through the mother — to all children. But severity can vary considerably even within a family. This is due to 'heteroplasmy': a single cell can contain both normal and mutant mitochondria, and the ratio between them determines how severe the disease manifests.
In 2015, the United Kingdom became the first country in the world to legalise mitochondrial donation — or, as the press calls it, the 'three-parent baby' technique. In 2023, the first child born using this technology in the UK was officially confirmed. This is not science fiction — it is clinical reality.
How it works, step by step:
How much DNA comes from the donor? The mitochondrial genome contains approximately 16,500 base pairs — roughly 0.1% of the total human DNA. The nuclear genome contains around 3.2 billion. The mitochondrial donor's contribution is vanishingly small: appearance, personality, intelligence, blood type — all of these are determined by nuclear DNA, which belongs 100% to the child's biological parents. |
If you do not have a mitochondrial disease, that does not mean the state of your mitochondria is irrelevant. Accumulation of mutations in mtDNA with age (somatic mutations, not inherited ones) is one of the mechanisms of cellular ageing. And lifestyle directly affects their function.
What supports mitochondrial health according to research:
The Premium material explores gene therapy, embryo editing, and the ethical frontier between healing and designing human life — from CRISPR to artificial wombs.
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