THE FIRST CELLS

1
THE FIRST CELLS
2

• 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.)

3

• SEM image of Microspheres

4

• coacervates collections of droplets that are
  composed of molecules that include linked amino
  acid and sugars.
• Coacervates can grow as cells can.

5

• 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.

6

• Sidney Fox showed how short chains of
• amino acids could cluster to form protocells.

7

• 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.)

8

• REAL LIVING CELLS
• The first cells were thought to be
• prokaryotic (no nucleus),
• anaerobic
• (cant live with oxygen),
• and heterotrophic (cant make food).
• 3.5 billion
• Year old microfossils

9

• 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.

10

• 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.

11

• 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
• Earths atmosphere.

12

• 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.

13

• 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.

14

• Smaller prokaryotes became incorporated inside
  larger prokaryotes.
• These smaller organisms eventually became
  mitochondria and chloroplasts ----organelles
  inside eukaryotic cells.

15

• These organelles that have some of their own
  genes (DNA). The genes are circular, similar to
  bacterial genes.

16

• In addition, mitochondria and chloroplasts of
  modern day eukaryotic cells can reproduce
  independently of the cells that contain them.