100 Fun Facts About Mitochondria

Mitochondria are popularly nicknamed the what of the cell?

Powerhouse fits because mitochondria generate most of the chemical energy a cell runs on; the cell biologist Philip Siekevitz spread the phrase with a 1957 magazine article of that title.

Which gas does the citric acid cycle inside mitochondria release as waste?

Carbon dioxide: the cycle strips the carbon out of food molecules, so when the body burns off fat, much of that fat ends up leaving through the lungs.

Like a mitochondrion, which of these has a double membrane?

Nucleus: its double membrane is pierced by pores, because the RNA copied from the DNA inside has to reach the rest of the cell, where proteins are built.

What are the folds of the inner mitochondrial membrane called?

Cristae greatly enlarge the inner membrane's surface, making room for more energy-producing machinery; mitochondria in muscle cells, which need more power, have more of them.

What is the fluid-filled space enclosed by a mitochondrion's inner membrane called?

The matrix is where the citric acid cycle turns, and it also holds the organelle's own DNA and ribosomes, leftovers from its free-living past.

Which of these components of the human body has no mitochondria at all?

A mature red blood cell throws out its mitochondria as it develops, leaving more room for haemoglobin; from then on it lives by fermenting sugar.

Which of these parts of the body has cells most densely packed with mitochondria?

The heart never rests, so its muscle cells are more densely packed with mitochondria than any other tissue; the kidneys, which filter the blood around the clock, come second.

Which hypothesis holds that mitochondria descend from free-living bacteria engulfed by an ancestral cell?

The endosymbiotic theory holds that the swallowed bacterium was kept rather than digested, trading energy for shelter until neither partner could live without the other.

Which biologist, Carl Sagan's first wife, argued that mitochondria began as bacteria?

Lynn Margulis set out the case in a 1967 paper that, by her own count, about fifteen journals rejected before one printed it; genetic evidence later turned her idea into textbook science.

Which plant-cell organelle shares the mitochondrion's origin, having started out as a free-living microbe swallowed by a larger cell?

The chloroplast began as a cyanobacterium swallowed by a cell that already had mitochondria, which is why plants and algae carry both organelles while animals have only one.

The cell that engulfed the mitochondrion's ancestor belonged to which group of microbes, famous for thriving in hot springs?

Archaea: the host was probably a relative of the Asgard archaea, first identified in 2015 in mud from near an Arctic vent field named Loki's Castle; all complex life descends from that merger.

What shape is the mitochondrial chromosome in most organisms?

Circular, like a bacterium's chromosome and unlike the cell's own linear ones, which is one of the clues that mitochondria were once free-living microbes.

How many genes does the human mitochondrial genome encode?

37 genes are all that remain: most of the ancestral microbe's genes were lost or moved into the cell's main genome, which now codes for about a thousand mitochondrial proteins.

The first complete human mitochondrial genome, published in 1981, is named after which English university city?

Cambridge: Fred Sanger's laboratory there read all 16,569 letters, and geneticists still describe a person's mitochondrial DNA by how it differs from a corrected version of that sequence.

Mitochondrial DNA passes only from mother to child, so which of these relatives shares yours?

Mother's mother: the same mitochondrial DNA runs down the female line from her to your mother to you, while your father's copy, inherited from his own mother, stops with him.

What molecular tag marks a sperm's mitochondria for destruction in the mammalian embryo?

Ubiquitin is the cell's 'dispose of this' label, and sperm mitochondria carry it into the egg; once they are broken down, a child's mitochondria normally all come from its mother.

The most recent common matrilineal ancestor of living humans is nicknamed 'Mitochondrial' what?

Eve was one woman among many in her day; she is singled out only because her mother-to-daughter line alone never broke, so everyone alive carries her mitochondrial DNA.

Which supposedly universal system do human mitochondria break by reading a few three-letter words differently?

The genetic code was assumed to be the same in all life until a 1979 study found that human mitochondria read UGA, a stop signal in the standard code, as the amino acid tryptophan.

Which notorious poison kills by jamming the final enzyme of the mitochondrial electron transport chain?

Cyanide binds the chain's last enzyme, so cells can no longer turn fuel into usable energy and suffocate from the inside, however well the blood supplies them.

The citric acid cycle that drives mitochondrial metabolism is also named after which biochemist?

Krebs worked out the cycle at Sheffield in 1937, four years after the Nazi government dismissed him from his German hospital post and he moved to England; it won him a Nobel Prize.

Which molecule, made from pyruvate or fatty acids, is the main fuel fed into the citric acid cycle?

Acetyl-CoA is the point where the breakdown of sugars, fats and proteins converges, which is why the body can burn all three in a single cycle.

The Warburg effect is the habit of which cells to ferment sugar even when their mitochondria could burn it fully?

Cancer cells mostly ferment glucose even when they could burn it completely, as Otto Warburg first noticed; the wasteful habit seems to free up raw materials for building new cells.

What is the final acceptor of electrons at the end of the mitochondrial electron transport chain?

Oxygen takes up the spent electrons at the end of the chain and is turned into water; this single reaction is the reason animals have to breathe.

The mitochondrial electron transport chain pumps which particles into the intermembrane space?

Protons, the positively charged cores of hydrogen atoms, pile up outside the inner membrane, creating a difference in both charge and acidity that the cell then taps for power.

Which process uses an ion gradient across the inner mitochondrial membrane to power the making of ATP?

Chemiosmosis was first received with scepticism, since it explained the cell's power supply by a mere build-up of ions across a membrane, yet it won its author a Nobel Prize.

Who won the 1978 Chemistry Nobel for showing how mitochondria store energy as a membrane gradient?

Peter Mitchell pursued the idea in a private laboratory he built inside a restored Cornish mansion, Glynn House, after stomach ulcers led him to resign from Edinburgh University.

Which rotary enzyme in the inner mitochondrial membrane makes the cell's main energy-carrying molecule?

ATP synthase is a true rotary motor: ions streaming through it spin a central shaft, and each turn presses ADP and phosphate together into fresh ATP.

Which channel protein lets the mitochondria of some cells release their stored energy as heat instead of making ATP?

Thermogenin short-circuits the usual energy-storing step so that fuel is burned straight into heat, which is how newborn babies keep warm without shivering.

Which tissue, rich in heat-generating mitochondria, is present at birth in humans and declines with age?

Brown fat owes its colour to the iron in its densely packed mitochondria; newborns carry it around the back, neck and shoulders, and it switches on in the cold.

Which protein, when it leaks out of a mitochondrion, sets off the cell's programmed self-destruction?

Cytochrome c normally just ferries electrons along the energy chain; once it escapes into the rest of the cell, it switches on the enzymes that take the cell apart.

Which channel proteins make the outer mitochondrial membrane freely permeable to small molecules?

Porins are barrel-shaped channels that bacteria also carry in their outer membranes, one of the family likenesses that mark mitochondria as descendants of bacteria.

In which part of a sperm cell are its mitochondria packed?

The midpiece holds a tight coil of mitochondria wrapped around the base of the tail, and their output powers the whip-like swimming that carries the sperm to the egg.

What is the orderly, programmed self-destruction of a cell, which mitochondria help to trigger, called?

Apoptosis lets an unwanted cell dismantle itself without harming its neighbours; it is how the webbing between an embryo's fingers and toes disappears.

Which cell part do mitochondria physically link with to exchange lipids and calcium signals?

The endoplasmic reticulum makes several membrane lipids that mitochondria cannot make for themselves, and hands them over at these contact points instead of shipping them in vesicles.

How do mitochondria multiply within a cell?

By binary fission, pinching in two as their bacterial ancestors did: a cell cannot build a mitochondrion from scratch, so every one comes from another mitochondrion.

During a long fast, liver mitochondria turn fat into which fuel that the brain can burn?

Ketones are made in the liver when fat is being broken down faster than it can be burned; they cross into the brain, which cannot run on fat itself, and stand in for glucose.

Which English king's skeleton, dug up in 2012, was identified by matching its mitochondrial DNA to living relatives?

Richard III lay under a Leicester car park; since mitochondrial DNA passes only through women, the match came from two descendants of his sister's all-female line.

Which extinct humans had their mitochondrial DNA read for the first time in 1997, from a fossil found in Germany in 1856?

Neanderthals' mitochondrial DNA fell outside the range of living people, which seemed to rule them out as our ancestors, until their full genome showed in 2010 that the two had interbred.

The Greek roots of 'mitochondrion' mean what?

Thread and granule, from the Greek mitos and khondrion: Carl Benda coined the name in 1898 for the look of the tiny grains, which tend to line up in threads.

Which British royal's mitochondrial DNA was used in 1993 to identify the bones of Russia's murdered last empress?

Prince Philip's maternal grandmother was the empress's sister, so he and Alexandra carried the same mitochondrial DNA down the female line, and it matched the bones exactly.

Which instrument first revealed the mitochondrion's folded inner membrane, in 1952?

Electron microscope: newly turned on cells at New York's Rockefeller Institute, it resolved what light microscopes never could, one membrane folded up inside another.

Which supplement-aisle staple is really an electron carrier from the mitochondrial energy chain, made naturally by the body?

Coenzyme Q10 passes electrons between the big enzymes of the energy chain; the body makes its own, but the amount in its tissues falls with age, which is the case made for taking it as a pill.

Which magazine ran Philip Siekevitz's 1957 article that gave mitochondria their famous nickname?

Scientific American began in 1845 as a weekly paper about new inventions; by 1957 it was the monthly in which working researchers, this Rockefeller cell biologist among them, explained their fields to lay readers.

Which of these diseases is caused by point mutations in mitochondrial DNA?

Leber's hereditary optic neuropathy can wipe out central vision within months, usually in young adults; because the fault lies in mitochondrial DNA, fathers never pass it on but mothers can.

Which country became the first to legalise IVF using a donor's mitochondria, in 2015?

The United Kingdom's Parliament approved it in February 2015 to stop mothers passing on mitochondrial disease; the child has two parents' DNA plus a donor's mitochondria, hence 'three-person baby'.

Which supplements were sold on the theory that by-products leaking from mitochondria cause ageing?

Antioxidants were promoted on a 1950s theory that free radicals cause ageing, yet a review of 78 trials found the supplements do not prolong life and some may shorten it.

Which medicines can harm mitochondria because the organelles' ribosomes resemble the ones the drugs were designed to attack?

Antibiotics such as the aminoglycosides jam bacterial ribosomes, and mitochondrial ribosomes are similar enough to be hit as well, one way these drugs can cause permanent hearing loss.

Which pathway begins the breakdown of glucose in the cytoplasm, before the mitochondria take over?

Glycolysis splits each glucose into two pyruvate molecules in the cytoplasm of nearly every living cell; mitochondria then burn the pyruvate for many times more energy.

Which acid do hard-working muscle cells make when they outpace their mitochondria and fall back on fermentation?

Lactic acid is the by-product of a shortcut that keeps energy flowing without mitochondria, at a price: about two ATP per glucose instead of roughly thirty.

Which enzyme in the outer mitochondrial membrane breaks down serotonin and is blocked by some antidepressants?

Monoamine oxidase clears away serotonin, dopamine and adrenaline once their message is sent; block it and they linger, which is how the MAO-inhibitor antidepressants lift mood.

In Star Wars, which life forms did George Lucas model on mitochondria?

Midi-chlorians arrived in The Phantom Menace in 1999, and Lucas called them a loose depiction of mitochondria, which also live inside cells in a kind of partnership.

Which outlaw's Missouri grave was opened in 1995 so mitochondrial DNA could confirm who lay in it?

Jesse James was shot by Robert Ford in 1882, and DNA from the exhumed remains matched that of his relatives in the female line.

A typical adult's cells, powered mainly by mitochondria, get through roughly how much ATP in a day?

Their own body weight in ATP, around 50 kilograms, passes through an adult's cells each day because every molecule is spent and rebuilt again and again.

When Dolly the sheep was cloned from a mammary cell, which animal supplied her mitochondria?

The egg donor's mitochondria stayed behind in the emptied egg, so Dolly was not a perfect genetic copy of the ewe whose mammary cell she grew from.

Mitochondrial DNA proved Anna Anderson was not Anastasia, lost daughter of which murdered tsar?

Nicholas II was shot with his family in 1918, and Anderson's DNA instead matched a relative of Franziska Schanzkowska, a missing Polish factory worker.

Mitochondrial DNA named the 'Unknown Child', a toddler buried in Halifax, Canada, after which disaster?

The Titanic sinking took the life of 19-month-old Sidney Goodwin from England, whom an earlier DNA test had wrongly named as a Finnish baby.

A disputed 2019 mitochondrial DNA study of an old shawl claimed to unmask which serial killer?

Jack the Ripper was named by the study as Aaron Kosminski, a Polish barber, but critics call the shawl's origin dubious and say others who handled it could share that DNA profile.

Which Victorian naturalist's decades of mystery illness have been blamed on a mitochondrial DNA fault?

Charles Darwin was ill for over forty years, and John Hayman of the University of Melbourne argued his symptoms fit cyclic vomiting syndrome, which is tied to mitochondrial DNA abnormalities.

Rigor mortis sets in because muscles, starved of ATP once mitochondria stop, can no longer do what?

Relax is the surprise: muscle fibres spend ATP to let go as well as to pull, so without it they cannot unlock.

All living humans inherit mitochondrial DNA from one woman, who is thought to have lived on which continent?

Africa was her home well over 100,000 years ago, and she was far from the only woman alive: hers is simply the one unbroken female line that survives.

Mitochondria are found in the cells of animals, fungi and which of these other living things?

Oak trees and every other plant need mitochondria as much as animals do: photosynthesis makes their sugar, and mitochondria turn that sugar into usable energy.

Mitochondrial DNA put a name in 1998 to the Unknown Soldier of which war at Arlington National Cemetery?

Vietnam War pilot Michael Blassie, shot down over South Vietnam in 1972, lay unnamed in the Tomb of the Unknown Soldier until the DNA test identified him.

Which baby with a mitochondrial DNA disorder was the subject of a 2017 London court fight that drew in the Pope?

Charlie Gard had mitochondrial DNA depletion syndrome, and both Pope Francis and President Trump spoke up for his parents as they sought an experimental treatment.

Which ice mummy, found in the Alps in 1991, has had his maternal line traced through mitochondrial DNA?

Ötzi the Iceman died more than 5,000 years ago, and DNA tests reached his wardrobe too: part of his coat came from a domesticated goat.

In 2000, mitochondrial DNA showed that a boy who died in a Paris prison was the son of which queen?

Marie Antoinette's hair was matched against a relic of the child, ending the claims of the many pretenders who said they were her escaped son, Louis XVII.

Mitochondrial DNA from hairs in an old book confirmed that bones under a Polish cathedral were which astronomer's?

Copernicus had owned the book, a calendar now kept in Uppsala in Sweden, for much of his life, and two hairs found inside it matched his teeth and thigh bones.

Which kind of exercise, as John Holloszy showed in the 1960s, prompts muscles to build more mitochondria?

Endurance training makes muscle cells multiply their mitochondria, which Holloszy discovered in 1967 by putting rats through weeks of treadmill running.

ATP, the energy-carrying molecule that mitochondria turn out, is short for which chemical name?

Adenosine triphosphate carries three phosphate groups in a row, and losing one or two of them is what pays for muscle contraction and nerve impulses.

Mitochondria are a hallmark of which great division of life, set apart from bacteria by complex cells?

Eukaryotes range from amoebas to whales, and nearly all of them carry mitochondria, whose DNA still resembles that of the bacteria they descend from.

Which process, carried out largely inside mitochondria, releases the energy stored in food and captures it as ATP?

Cellular respiration yields about 30 ATP molecules per glucose molecule in practice, short of the 38 that biology textbooks often quote, because some energy leaks away.

Faults in PINK1, a gene that flags worn-out mitochondria for disposal, cause an early form of which brain disorder?

Parkinson's disease kills dopamine-making neurons, and many of the pesticides linked to it are mitochondrial poisons, which points to failing mitochondria as a shared cause.

A mitochondrial gene bred into hybrid seed left which US crop open to a devastating blight in 1970?

Corn carrying 'Texas' cytoplasm made up about 90% of the crop, so when a fungus evolved a toxin aimed at its mitochondria the blight destroyed 15% of the harvest.

Which laboratory microbe can survive with no mitochondrial DNA at all, forming undersized colonies nicknamed 'petites'?

Budding yeast can fall back on fermenting sugar, so it survives the loss, and Boris Ephrussi's team in France described the stunted colonies in 1949.

A Somerset history teacher was found in the 1990s to share a mitochondrial DNA lineage with which ancient skeleton?

Cheddar Man is the oldest nearly complete skeleton found in Britain, and teacher Adrian Targett shares his lineage with so many other people that no direct descent is proven.

Mitochondrial DNA from a finger bone found in a Siberian cave revealed which unknown human group in 2010?

Denisovans ranged across Asia until about 32,000 years ago, yet most of what is known about them still comes from DNA instead of fossils.

Which sequel to A Wrinkle in Time sends its heroes inside a mitochondrion to save Meg Murry's sick brother?

A Wind in the Door grew out of two articles about mitochondria that a physician friend gave Madeleine L'Engle while she was struggling to develop the story.

Rickettsia prowazekii, often called the closest living relative of mitochondria, causes which louse-borne disease?

Epidemic typhus bacteria can live only inside other cells, as the ancestor of mitochondria came to do, and they are named after a researcher whom the disease killed in 1915.

Which North American swamp plant melts its way through frozen ground using heat made by its mitochondria?

Skunk cabbage can run 15 to 35 °C warmer than the surrounding air, because a bypass enzyme lets its mitochondria give off energy as warmth instead of storing it.

Which common type 2 diabetes pill, traced back to the French lilac plant, is thought to act partly on mitochondria?

Metformin's best-known proposed mechanism is that it slows complex I, the first stage of the mitochondrial energy chain, although several other targets have been suggested.

Which compound, also sold as a sports supplement, ferries long-chain fatty acids into mitochondria to be burned?

Carnitine takes its name from the Latin for flesh, because it was first extracted from meat in 1905, and meat-eaters still take in far more of it than vegans.

Mitochondria carry out the first step in turning which waxy molecule into steroid hormones such as cortisol?

Cholesterol is clipped into pregnenolone inside mitochondria, the slowest step of the whole process and the starting point for every human steroid hormone.

Which B vitamin does the body turn into NAD, the shuttle that carries electrons to the mitochondrial energy chain?

Niacin (B3) is so vital to NAD supply that a lack of it causes pellagra, a disease marked by skin and mouth sores, headaches and tiredness.

The mitochondrial enzyme ALDH2, sluggish in many East Asians, clears which toxic by-product of drinking alcohol?

Acetaldehyde lingers when the enzyme is weak, and about 36% of East Asians lack a working mitochondrial version, which is what brings on the facial 'alcohol flush'.

Rotenone, a plant poison that blocks the mitochondrial energy chain, was used for centuries to catch which animals?

Fish absorb the poison readily through their gills, and it is still approved for clearing unwanted species from lakes and rivers.

Which chemical from First World War munitions plants became a diet drug by making mitochondria waste fuel as heat?

Dinitrophenol (DNP) raises energy use by 30 to 40 percent, but an overdose can push body temperature as high as 44 °C and kill.

Which double Nobel laureate led the team that first read the complete human mitochondrial genome?

Fred Sanger used the DNA-reading method that earned him his second Nobel to spell out all 16,569 letters of the mitochondrial genome.

Which species-identification method, proposed in 2003, reads a short stretch of one mitochondrial gene?

DNA barcoding works because the chosen gene differs just enough between animal species to tell them apart, much as a shop scanner tells one product from another.

Ancestry tests sort people's mitochondrial DNA into lettered maternal lineages known as what?

Haplogroups carry letter names running from A to Z, and the mitochondrial ones fall into three main groups labelled L, M and N.

The kinetoplast is a giant tangle of mitochondrial DNA in the parasites behind which African disease?

Sleeping sickness parasites store their mitochondrial DNA as large and small rings linked into a flat sheet that resembles chain mail.

In which shellfish do fathers hand their mitochondrial DNA on to their sons, breaking the usual rule?

Mussels of the family Mytilidae pass the father's mitochondria to sons alone, where they settle in the reproductive organs; daughters keep only the maternal set.

Henneguya, a jellyfish relative that has no mitochondrial DNA at all, is a parasite of which animal?

Salmon carrying the parasite develop 'tapioca disease', and the creature is one of only a handful of truly anaerobic animals known.

Which gut parasite of humans and other vertebrates keeps only shrunken mitochondria called mitosomes?

Giardia's mitosomes make no ATP at all: they survive only to help finish iron-sulfur proteins, a job the parasite cannot do without.

What is the name for a cell's selective recycling of its damaged mitochondria?

Mitophagy was caught on camera in 1962, when electron microscope images showed fragments of mitochondria inside liver lysosomes, the cell's recycling sacs.

What term describes a single cell holding a mixture of normal and mutated mitochondrial DNA?

Heteroplasmy helps explain why some mitochondrial diseases range from mild to severe: the larger the share of faulty DNA copies, the worse the illness tends to be.

Along which tracks of the cell's skeleton are mitochondria hauled down the long fibres of nerve cells?

Microtubules run the whole length of a nerve fibre, and motor proteins called kinesins walk along them carrying mitochondria as cargo.

Which German scientist coined the word 'mitochondria' in 1898, after seeing the structures form long chains?

Carl Benda spotted hundreds of the tiny bodies using a crystal violet stain, and at first assumed they were there to reinforce the cell's structure.

A 2024 mitochondrial DNA study ruled out the legend that which German foundling was a kidnapped prince of Baden?

Kaspar Hauser appeared in Nuremberg in 1828 claiming to have grown up alone in a darkened cell, and five years later he died of a stab wound.

Mitochondrial DNA studies showed that which extinct South African grazer was no separate species after all?

The quagga turned out to be a subspecies of the plains zebra, and in 1984 it became the first extinct animal to have its DNA analysed.

The mitochondrial disease MELAS takes the final letter of its name from which sudden brain events?

Strokes, or strictly 'stroke-like episodes', supply the S; the condition was first described under the name MELAS in 1984 and is inherited through the female line.

Which Nobel laureate, first to isolate vitamin C, also uncovered key steps of the mitochondrial citric acid cycle?

Szent-Györgyi won the 1937 Nobel Prize for work on biological combustion, and in some experiments he used Hungarian paprika as his source of vitamin C.