Download THE FIRST CELLS

THE FIRST
CELLS
Laboratory experiments in the early 20th
century proved that cell like structures could
have come from simple organic molecules.
• Microspheres, small spheres of proteins
organized into a membrane,
(These structures many life-like properties such
as the ability to take in materials from their
surroundings. They
can also bud and form
smaller microspheres.)
SEM image of Microspheres
• coacervates collections of droplets that
are composed of molecules that include
linked amino acid and sugars.
• Coacervates can grow as cells can.
Sidney Fox – an American biochemist
Produced “protocells” by heating a solution
of amino acids. The protocell structure
was enclosed by a membrane could grow
and divide.
• Sidney Fox showed how short chains of
amino acids could cluster to form protocells.
The Role of RNA
Thomas Cech
(1989) found that an RNA
molecule could act as an
enzyme (ribozyme),&
promote chemical reactions.
(Perhaps this self-replicating RNA may have
started evolving inside simple cell-like structures
and provided the hereditary information.)
REAL LIVING CELLS
The first cells were thought to be
prokaryotic (no nucleus),
anaerobic
(can’t live with oxygen),
and heterotrophic (can’t make food).
3.5 billion
Year old microfossils
Autotrophs were next.
• As competition for organic compounds
occurred in the primitive organic pools and
seas, the environment favored the
development of autotrophs, the cells that
could make their own food.
The first autotrophs were
chemosynthesizers. They were
probably similar to present day
archaebacteria which are prokaryotic and
live in harsh environments
such as volcanic or deep sea vents.
The next autotrophs were the
photosynthesizers. These were ancient
single-celled ancestors to algae and
plants. Cells such
as the cyanobacteria
released free
oxygen to the
Earth’s atmosphere.
After a billion years, the photosynthesizing
cells released oxygen close to present day levels.
Ultraviolet energy from the sun split O2 to
Form O3 –ozone. It formed a UV barrier in
the atmosphere to allow life to flourish on
Earth.
The First Eukaryotic Cells
They may have had their
start about 2 - 1.5 billion
years ago. According to
a hypothesis known as
Endosymbiosis.
It is proposed by Lynn
Margulis in 1970.
• Smaller prokaryotes became
incorporated inside larger prokaryotes.
• These smaller organisms eventually
became mitochondria and chloroplasts ---organelles inside eukaryotic cells.
• These organelles that have some of
their own genes (DNA). The genes are
circular, similar to bacterial genes.
• In addition, mitochondria and chloroplasts
of modern day eukaryotic cells can
reproduce independently of the cells that
contain them.