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Cell Biology Topic 1.5 Origin of Cells • According to the cell theory, all cells come from pre-existing cells • Sperm and egg join to make a zygote • Zygote divides repeatedly to form embryo • What about the first cell?? • They would need to have arisen from nonliving material Origin of Cells • Spontaneous generation is the formation of living thins from non-living matter • Theophratus- Silphium plant • Aristotle-insects from dew or hair • Paracelus-mice from decaying matter • Francesco Redi-rotting meat and flies Origin of cells Origin of Cells • Louis Pasteur spontaneous generation experiments • Boiled (control) and unboiled (experimental)broth in long necked flasks Origin of cells • Cells may have formed over hundreds of millions of years of evolution • In a series of stages: 1. Production of carbon compounds such as amino acids and sugars 2. Assembly of carbon compounds into polymers 3. Formation of membranes 4. Development of a mechanism of inheritance Origin of cells • Miller and Urey simulated the earth’s early atmosphere • They were able to produce amino acids and other carbon compounds needed for life Origin of cells • Deep ocean vents also simulate the early earth • Provide and energy source for the formation of carbon compound polymers • Iron sulfide • chemosynthesis Origin of cells • Formation of membranes • Creates an inside environment different from the outside • Phospholipids behave this way naturally • Show video! Origin of cells • Mechanism of inheritance • In order for DNA to replicate it needs enzymes(catalysts) , but enzymes are coded by genes • “chicken and the egg” • May have been an earlier stage where RNA was the genetic material • It can act as genetic material and a catalyst Origin of cells Endosymbiotic theory • Supports the evolution of some prokaryotes into eukaryotes • Theory that mitochondria and chloroplasts were once free living prokaryotes • Larger anerobic prokaryotes took them in by Endocytosis (engulfing) but did not eat them! • They were instead used for energy production Endosymbiotic theory • Symbiotic relationship/mutualism • Large prokaryote provides food and small prokaryote provides energy Endosymbiotic theory Evidence that supports the theory: • Both chloroplasts and mitochondria contain their own DNA (circular piece of DNA similar to other prokaryotes) • They also contain ribosomes that are similar to the ribosome found in prokaryotes (70s subunits) • They also produce some of their own proteins • They can only be produced by division of preexisting mitochondria/chloroplasts Endosymbiotic theory
