THE FIRST CELLS

THE FIRST CELLS

Laboratory experiments in the early 20th

century proved that cell like structures couldhave 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 solutionof amino acids. The protocell structurewas enclosed by a membrane could growand divide.

• Sidney Fox showed how short chains ofamino 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 billionYear old microfossils

Autotrophs were next. • As competition for organic compoundsoccurred in the primitive organic pools andseas, the environment favored thedevelopment of autotrophs, the cells thatcould 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 photosynthesizingcells released oxygen close to present day levels. Ultraviolet energy from the sun split O2 toForm O3 –ozone. It formed a UV barrier inthe atmosphere to allow life to flourish onEarth.

The First Eukaryotic Cells

They may have had theirstart 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.