The Origin of Cells

The Origin of Cells

1. Cells can only be formed by division of existing cells

   • The first cells must have arisen from non-living material
     • The origin of eukaryotic cells can be explained by the endosymbiotic theory

2. Origin of the First cells

   • the first cells must have arisen from non living material (this is the most logical assumption, however it is still confusing to scientists)
     • hypotheses for how this statement occurred:
       • 1. Production of carbo compounds such as sugars and amino acids
         • simulation of early earth atmosphere to see what would be produced; 13/20 of naturally occurring amino acids were found
         • 2. Assembly of carbon compounds into polymers
           • 3. Formation of Membranes
             • 4. Development of a mechanism for inheritance

3. Endosymbiosis & Eukaryotic Cells

   • The Origin of Eukaryotic cells can be explained by the endosymbiotic theory
   • Theory of Endosymbiosis
     • Mitochondria were once free-living prokaryotic organisms that had developed the process of aerobic cell respiration
       • Larger prokaryotes that could only respire anaerobically took them in by endocytosis
         • symbiotic relationship = smaller prokaryotes help larger prokaryotes and larger prokaryotes allow small prokaryotes to live in larger prokaryotes cytoplasm
     • also explains origin of chloroplasts
       • if prokaryote with photosynthesis was taken in by a larger cell => could've developed into the chloroplasts of photosynthetic eukaryotes
   • Although no longer capable of living independently, chloroplasts and mitochondria both have features that suggest they evolved from independent prokaryotes
     • a. they have their own genes, on a circular DNA molecule like that of prokaryotes
     • b. they have their own 70S ribosomes of a size and shape typical of same prokaryotes
     • c. they transcribe their DNA and use the mRNA to synthesise some of their own proteins
     • d. they can only be produced by division of pre-existing mitochondria and chloroplasts