Mitochondria
The other life inside your cells
Every cell in your body hosts the descendants of a bacterium. Scroll to watch the merger from over a billion years ago: a bacterium was taken inside another cell, handed over most of its genes, and became the mitochondrion.
A bacterium that could use oxygen, a distant relative of today’s alphaproteobacteria, living on its own.
Schematic: sizes and timescales are simplified. Details of the merger, such as its order and what the host looked like, are still debated.
Every cell in your body hosts the descendants of a bacterium. Scroll to watch the merger from over a billion years ago: a bacterium was taken inside another cell, handed over most of its genes, and became the mitochondrion.
Three questions this topic answers
Why do mitochondria have their own DNA?
What does the “powerhouse of the cell” metaphor leave out?
Can NAD+ supplements really slow human ageing?
A generator that spins
Feed in NADH and watch electrons pass down the respiratory chain, pumping protons across the membrane, which then spin ATP synthase. Try cutting off the oxygen, or opening the brown-fat proton leak.
Without oxygen, electrons jam at complex IV and the whole chain stops. This is why lack of oxygen, or cyanide poisoning, drains a cell of energy so fast.
Protons slip back into the matrix without passing through ATP synthase, so the energy becomes heat. Brown fat uses UCP1 to keep the body warm this way.
The two electrons from each NADH pass through complexes I, III and IV and pump about 10 protons. The human ATP synthase rotor has 8 subunits: 8 protons turn it once and make 3 ATP. After the cost of importing raw materials, each NADH yields about 2.5 ATP. For every 2 electrons, complex IV turns half an oxygen molecule into one water molecule.
Chapter manifest
Each chapter is stamped with the evidence level of its main claim. Chapter text is not written yet; this lists the plan.
- MT-CH01
An ancient merger
A bacterium moved into a host cell and slowly became a permanent organelle. The broad story is agreed; the details are still debated.
Consensus 7 min In progress - MT-CH02
A rotary motor in every cell
The electron transport chain turns food energy into a proton gradient, which spins ATP synthase like a turbine.
Consensus 8 min In progress - MT-CH03
More than a powerhouse
Mitochondria also make building blocks, keep redox balance and handle metabolic waste.
Consensus 7 min In progress - MT-CH04
Splitting, merging and recycling
Mitochondria constantly divide and fuse, and damaged parts are taken apart and recycled.
Consensus 6 min In progress - MT-CH05
Genes from your mother
Mitochondrial DNA is inherited almost only from the mother. This lets scientists trace maternal ancestry and raises ethical questions about mitochondrial replacement therapy.
Consensus 7 min In progress - MT-CH06
Ageing, NAD+ and supplements
NAD+ levels fall with age, and restoring them helps in animals. Whether that works, and is safe, in humans still needs clinical evidence.
Limited evidence 9 min In progress - MT-CH07
Breathing ends in water
The oxygen you breathe ends up as water inside your mitochondria.
↔ links to the other topicConsensus 5 min In progress
Three claims about boosting mitochondria
Pick whether you believe it, then see what the literature says. The full case is in chapter 6.
Regular endurance exercise makes muscles build more mitochondria.
This is one of the most solid findings in exercise physiology: training switches on mitochondrial biogenesis, with PGC-1α as a key regulator.
Taking NMN or NR to restore NAD+ slows human ageing.
Animal results are promising, but whether restoring NAD+ slows human ageing, and whether it is safe long term, is still unanswered. (Covarrubias 2021)
CoQ10 supplements slow ageing in healthy people.
CoQ10 really is an electron carrier in the respiratory chain, but needing it is not the same as benefiting from more. Human evidence for anti-ageing effects in healthy adults is lacking.
Key references
Each entry was checked against PubMed and links to the original by DOI.
- Roger AJ, Muñoz-Gómez SA, Kamikawa R. (2017). The origin and diversification of mitochondria. Curr Biol, 27(21), R1177–R1192. How a bacterium became the mitochondrion, and which details are debated. Opening animation and chapter 1. doi:10.1016/j.cub.2017.09.015
- Spinelli JB, Haigis MC. (2018). The multifaceted contributions of mitochondria to cellular metabolism. Nat Cell Biol, 20(7), 745–754. What mitochondria do beyond energy: building blocks, redox balance, waste. Chapters 2–3. doi:10.1038/s41556-018-0124-1
- Covarrubias AJ, Perrone R, Grozio A, Verdin E. (2021). NAD+ metabolism and its roles in cellular processes during ageing. Nat Rev Mol Cell Biol, 22(2), 119–141. Evidence that NAD+ declines with age, and open questions about restoring it in humans. Chapter 6. doi:10.1038/s41580-020-00313-x