Evolution of the cell

• 4.5 million years ago

  formation of the solar system 
• 4 million years ago

  • Water condensation as earth cools down
  • Formation of earth crust
  • Formation of organic molecules
• 3 billion years ago

  Stromatolites indicate first life at 1 billion years after earth formation (sediments of fossil cyanobacteria-like microbes)
• 3 billion years ago

  • Photosynthesis developed in cyanobacteria-like microbes
  • Oxygen in the atmosphere
• 2 billion years ago

  Development of eukaryotic cells that contain symbiotic prokaryotes (later established as chloroplasts and mitochondria)
• 1 billion years ago

  Appearance of multi-cellularity
• 0.5 billion years ago

  "Cambrian explosion" (550-500 million years ago) of multi-cellular life forms, symmetrical, with antenna and segmented
• how are ribozymes formed

  Single stranded RNA can fold and form molecules that catalyze chemical reactions
• RNA world hypothesis

  • RNA was at the origin of life (stored genetic information and catalyze chemical reactions)
  • Alexander Rich, 1962
• how do ribozymes produce new replicates

  1. the ribozyme replicates an un-folded RNA strand of another replicase molecule
  2. At high temperature, both strands separate; one folds into a new replicase, one serves as template for further synthesis
• how do RNA replicase and vesicles produce a protocol

  • The RNA replicase uses ribonucleotides to make a copy of another RNA replicase
  • Micelles fuse with the vesicle and enlarge it until it becomes unstable and divides
  • Random mistakes could form better replicases, and uptake of new RNAs could incorporate new ribozymes, which could make the protocell grow and divide faster
  • Protocells compete for resources (fatty acids, ribonucleotides) and faster growing protocells are more competitive (evolution)
• what is symbiosis

  Interaction between two different organisms living in close physical association, typically to the advantage of both.
• what is cellular endosymbiosis

  when a single cell organism lives in a host cell
• mechanism of endosymbiosis

  1. Phagocytosis of a prokaryote
  2. Host cell and endosymbiont reproduce
  3. Development of an interdependence
• who proposed the endosymbiosis theory

  Lynn Margulisin 1967
• endosymbiont hypothesis

  Mitochondria and Chloroplasts derived from engulfed prokaryotes
• how was the eukaryotic cell formed

  • Infolding of membrane forms nucleus and the endoplasmic reticulum
  • Engulfing of heterotrophic prokaryote results in mitochondria
  • Engulfing of photosynthetic prokaryote results in chloroplasts
• evidence mitochondria and chloroplasts are derived from prokaryotes

  1. They have their own circular genome
  2. They contain 70S ribosomes
  3. Chloroplasts use the tubulin-like FtsZ for division
  4. Chloroplasts and cyanobacteria have thylakoid membranes
  5. Both are surrounded by a double membrane
  6. Bacteria and mitochondria share a specific membrane lipid