the first cells
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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 , - PowerPoint PPT PresentationTRANSCRIPT
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THE FIRST CELLS
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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.)
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SEM image of Microspheres
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• coacervates collections of droplets that are composed of molecules that include linked amino acid and sugars.
• Coacervates can grow as cells can.
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Sidney Fox – an American biochemist Produced “protocells” by heating a solutionof amino acids. The protocell structurewas enclosed by a membrane could growand divide.
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• Sidney Fox showed how short chains ofamino acids could cluster to form protocells.
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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.)
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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
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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.
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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.
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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.
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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.
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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.
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• Smaller prokaryotes became incorporated inside larger prokaryotes.
• These smaller organisms eventually became mitochondria and chloroplasts ----organelles inside eukaryotic cells.
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• These organelles that have some of their own genes (DNA). The genes are circular, similar to bacterial genes.
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• In addition, mitochondria and chloroplasts of modern day eukaryotic cells can reproduce independently of the cells that contain them.