1.5 The Origin of Cells 1.5 The origin of cells Understanding Cells can only be formed by division of pre-existing cells First cells must have arisen from
non-living material Origin of eukaryotic cells can be explained by endosymbiotic theory Applications * Evidence fro Pasteurs experiments that spontaneous generation of cells &
organisms does not now occur on Earth Nature of Science * Testing the general principles that underlie the natural world: the principle that cells only come from pre-existing cells needs to be verified
Understanding: Cells can only be formed by division of pre-existing cells Our trillions of cells originated from one single zygote Theres a continuity of life from its origins on Earth to our bodies today.
Have not been able to create artificial cell from non-cell materials Nature of Science: Verifying general principles that underlie the natural world: the principle that cells only come from pre-existing cells needs to be verified. Spontaneous generation = living from non-living * Theophrastus Silphium from soil * Aristotle insects from dew, hair, flesh, feces
* Paracelsus mice, frogs, eels from water, air, decaying matter Cells only come from pre-existing cells * Redi maggots & rotting meat experiment * Spallanzani boiled soup experiment * Pasteur swan-necked flask experiment * Todays scientists know: 1) Cells are highly complex! 2) The only thing that produces more cells is cell division.
3) Viruses are not cells & can only be produced inside host cells Francesco Redi (1600s) Lazzaro Spallanzani (1700s) Application: Evidence from Pasteurs experiments that spontaneous generation of cells & organisms
does not now occur on Earth (1800s) Understanding: First cells must have arisen from non-living material How did cells gets here in the first place? Theory 1: panspermia (seeds everywhere!) first cells on earth came from outer space Directed Panspermia proposed by Francis Crick (co-discoverer of
double helix) in 1973 = seeds purposely spread by an advanced extraterrestrial civilization, or can be spread from Earth to other planets by humans Crick found it impossible that the complexity of DNA could have evolved naturally or Theory 2: cells arose from nonliving material on Earth Complex structures cant arise by evolution it would have to happen
in tiny steps over millions of years: 1. 2. 3. 4. Production of C compounds (sugars & amino acids) Assembly of C compounds into polymers
Formation of phospholipid membranes Development of mechanism for inheritance 1.Production of C compounds (sugars & amino acids) Miller & Urey experiment 2. Assembly of C compounds into polymers (in deep sea vents where chemicals supplied
energy needed) 3.Formation of phospholipid membranes 4. Development of mechanism for inheritance
Which came first? Creation of DNA or creation of proteins (enzymes)? For DNA replication & DNA transcription/translation, you need enzymes. But to get enzymes, you need DNA to code for them. Solution: RNA was first genetic material it can act as a catalyst and can self-replicate! Understanding: Origin of eukaryotic cells can
be explained by endosymbiotic theory Endo = inside Symbiosis = mutualistic = relationship where both organisms benefit Small aerobic or photosynthetic prokaryote taken into larger anaerobic prokaryote by endocytosis * Small one is supplied with food * Large one is supplied with energy Endosymbiotic theory = small prokaryotes living inside big ones
developed into mitochondria and chloroplasts. Endosymbiotic theory Endocytosis vs Exocytosis Mitochondria & chloroplast similar to prokaryotes: Circular DNA
70s ribosomes Use DNA to make their own proteins Can only be produced by division of pre-existing mitochondria & chloroplasts
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