50 Fun Facts About Mitochondria

Mitochondria are popularly nicknamed the what of the cell?

The phrase was popularised by Philip Siekevitz in a 1957 magazine article of that name.

Which energy-carrying molecule do mitochondria generate through aerobic respiration?

Making it aerobically yields far more energy than fermentation does.

How many membranes does a mitochondrion have?

The outer one is leaky to small molecules; the inner one is highly impermeable and packed with proteins.

What are the folds of the inner mitochondrial membrane called?

They boost surface area; muscle mitochondria, which need more ATP, have more of them.

What is the fluid-filled space inside the inner membrane called?

It holds about two-thirds of the organelle's protein, its ribosomes and several copies of its DNA.

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

A liver cell, by contrast, has a great many.

Roughly how many mitochondria can a single liver cell contain?

Numbers vary hugely by tissue and by how much energy the cell needs.

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

The relationship began deep in the Precambrian and gave the host cell the ability to respire.

Which biologist popularised the endosymbiotic origin of mitochondria?

The idea gained acceptance once it was clear mitochondria have bacteria-like genomes and 70S-type ribosomes.

The ancestor of mitochondria was probably closely related to which order of bacteria?

That places it among the alphaproteobacteria, though the exact relationship is still argued over.

Roughly how long ago did the symbiotic relationship that produced mitochondria probably begin?

Respiring bacteria would have been a huge advantage to a host that only knew glycolysis and fermentation.

What shape is the mitochondrial chromosome in most organisms?

That is another bacterial trait; a mitochondrion may hold two to ten copies of it.

How many genes does the human mitochondrial genome encode?

That is 13 protein subunits, 22 tRNAs and 2 rRNAs.

Approximately how long is the human mitochondrial genome?

It is a double-stranded circle with almost no non-coding DNA and no introns.

From which parent do humans normally inherit their mitochondrial DNA?

The sperm's mitochondria enter the egg but are tagged for destruction.

What molecular tag marks paternal mitochondria for destruction in the embryo?

Some conifers, by contrast, normally pass mitochondria down the paternal line, though not pines and yews.

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

The date is often taken as support for a recent modern-human expansion out of Africa.

In 1979 researchers found that human mitochondrial genes use what?

AUA, AUC and AUU can all serve as start codons; most plant mitochondria stick to the standard code.

The mitochondrial genome of which parasite is unusually split into 18 tiny minichromosomes?

The same pattern is found in other sucking lice but not in chewing lice.

The citric acid cycle at the heart of mitochondrial metabolism is also named after which biochemist?

Each turn produces three NADH, one FADH2 and one GTP.

Which molecule, made from pyruvate or fatty acids, is the only fuel that enters the citric acid cycle?

One is consumed per turn and, unlike the cycle's intermediates, is never regenerated.

Which citric acid cycle enzyme is bound to the inner membrane as part of Complex II?

All the other cycle enzymes are dissolved in the interior.

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

At complex IV it reacts with a reduced iron-carrying protein to make water, releasing 218 kJ per mole.

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

The resulting gradient drives them back through a rotary enzyme, which spins out ATP.

What process uses the proton gradient across the inner membrane to drive ATP synthesis?

The scientist who described it won the 1978 Nobel Prize in Chemistry.

Who received the 1978 Nobel Prize in Chemistry for the chemiosmotic theory?

Boyer and John Walker shared part of the 1997 prize for working out how the ATP-making enzyme itself operates.

Which enzyme complex in the inner membrane actually makes ATP from ADP and phosphate?

The small round F1 particles studding the inner membrane folds are its heads.

What is the name of the proton channel that lets some mitochondria release energy as heat instead of ATP?

Also called UCP1, it drives non-shivering thermogenesis in newborns and hibernating animals.

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

It is at its highest in early life and in hibernating mammals.

Which protein, released from the intermembrane space, triggers apoptosomes and programmed cell death?

Mitochondria have long been recognised as central to the intrinsic pathway of apoptosis.

What are the pore-forming proteins in the outer mitochondrial membrane called?

The main one, VDAC, forms a beta barrel much like those in the outer membrane of gram-negative bacteria.

Which unusual four-chained phospholipid is characteristic of the inner mitochondrial membrane?

It was first found in cow hearts in 1942 and is otherwise typical of bacterial membranes.

What are mitochondria called once they have been stripped of their outer membrane?

Mitosomes and hydrogenosomes are instead the shrunken mitochondrion-related organelles of some anaerobic eukaryotes.

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

The contact zone is called the MAM, the mitochondria-associated ER membrane.

How do mitochondria multiply within a cell?

It is a bacterial trick, though the host cell regulates it; cryo-electron tomography suggests they may actually bud.

Which mitochondrion-lacking group of eukaryotes includes Monocercomonoides?

They seem to have lost the organelle entirely, with cytoplasmic proteins taking over some functions.

Who first observed structures that were probably mitochondria, in insect muscle, in 1857?

Altmann later called them 'bioblasts' in 1890.

Who coined the word 'mitochondria' in 1898?

It comes from the Greek for 'thread' and 'granule'.

The Greek roots of 'mitochondrion' mean what?

Under the microscope they can look like tiny threads or grains.

Which dye did Leonor Michaelis show in 1900 could stain mitochondria in living cells?

It stayed the standard way to see them until electron micrographs arrived in the 1950s.

In which year did the first electron micrographs confirm mitochondria's double membrane?

They showed the inner membrane folded into ridges dividing up the interior.

Which two scientists showed in 1948 that mitochondria are the site of oxidative phosphorylation?

Claude's tissue-fractionation method had made it possible to study isolated mitochondria.

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

The author was Philip Siekevitz.

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

MELAS and MERRF syndromes are others; they are passed almost always from mother to child.

Which IVF technique uses donor mitochondria to stop mtDNA diseases being passed on?

It is still being researched and raises ethical questions because it amounts to a heritable genetic change.

Which electron transport chain by-products are blamed in the mitochondrial free radical theory of ageing?

The idea that oxidative stress drives ageing dates from 1956.

The ribosomes inside mitochondria most closely resemble which kind?

That is one of the strongest pieces of evidence for the bacterial ancestry of the organelle.

In 1904 Friedrich Meves first observed mitochondria in plants, in cells of which flower?

With Claudius Regaud he went on to suggest in 1908 that they contained proteins and lipids.

How much more ATP does aerobic respiration yield from glucose than fermentation does?

When O2 runs short, cells fall back on fermentation, which does not need mitochondria at all.

Which enzyme that breaks down neurotransmitters such as epinephrine sits in the outer mitochondrial membrane?

The outer membrane also hosts enzymes for elongating fatty acids and degrading tryptophan.