THE FIRST CELLS

Laboratory experiments in the early 20 th 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 O 2 to Form O 3 –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 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.