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ever y t hing in t he cell membra ne aside
from the nucleus. Around 1835, the
French biologist Félix Dujardin saw
this ‘life substance’ in single-celled
animals and named it sarcode
(meaning ‘the flesh of the cell’).
In the mid-19th century, life was
made a little easier for the nascent
field of cell biology. Until this point a
variety of natural dyes such as iodine,
cochineal and van Leeuwenhoek’sof t he best-k now n orga nelles is t he
mitochondrion, now known as the
cell’s ‘powerhouse’ because it
produces a molecule t hat is used as a
sou rce of chemical energy. It’s possible
that mitochondria were first seen in
muscle cells by the Swiss physiologist
Albert von Kölliker in 1857. But it was
Richard Altmann, in 1894, who
established that they were organelles
a nd called t hem ‘bioblasts’. They 5Sometimes major scientific discoveries happen by chance, as Alber t Claude found when
he stumbled upon a key organelle while searching for a virus in the cells of a chickenTHE KEY EXPERIMENT
saffron had been used to stain cells.
But in 1856, a young assistant chemist
named William Perkin produced
mauve, the first synthetic dye. Though
not designed for cells, it was the first
of many useful synthetic dyes.Internal organelles
Many cellular metabolic processes
take place in the cytosol, but some
occur in dedicated organelles. OneMuch was known about the cell by
the time that Albert Claude performed
his key experiment of developing cell
fractionation in 1930. But looking down a
microscope was quite different to being
able to separate out the parts of the cell
to study them individually.
Claude developed cell fractionation
while trying to isolate a virus, called Rous
Sarcoma Virus, from chicken tumours.
To do this he gently mashed up the
tumour cells with a pestle and mortar (or
sometimes a commercial meat grinder)
to break the membranes and release the
cell contents. He then put them in a tube
and spun them in a centrifuge, the force
of which speeds up the settling of heavier
particles to the bottom of the tube. By
successively spinning and extracting the
sediment, the components of the cells are
separated by size.
Claude found what he was looking
for – a virus made of Ribonucleic acid
(RNA). Good scientists run ‘control’
experiments too. In this case, Claude
needed to show that the virus was
present in only the tumour cells, and
not healthy chicken cells. But when he
repeated the process, he found that
healthy cells also had similar RNA-rich
particles in them. He named these
mysterious organelles ‘microsomes’,
discovering for the first time an organelle
that researchers using a light microscope
simply would not have spotted.Albert Claude serendipitously discovered
a cell organelle, the microsome, when
searching for a virus using a centrifuge“The mitochondrion is the cell’s ‘powerhouse’
because it produces a molecule that is
used as a source of chemical energy”
THE COMPOSITION OF HUMAN CELLS