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Lecture 3

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Western University
Biology 1001A

Lecture 3: Origins of Life  Viruses depends on other form of life, they have DNA and proteins, they can evolve  Earth is 4.6 billion years old (should know the number 4.6 billion years)  Geological evidence dates back to 3.5 billion years ago; Stromatolites  o Cyanobacteria o  Photosynthesis  Start of life might be started around 4.0 billion years ago  3 branches from the tree of life: Bacteria, archaea, eukaryotes (PP p. 4)  o LUCA: last universal common ancestor o  every kind of life right now is derived from the last universal common ancestor o All three branches have in common: o  Cells made of lipids  Genetic system based on DNA  DNA to RNA to protein transfer of information  Common system of protein assembly  ATP, metabolism  glucose and glycolysis  What came before LUCA  o Many forms of life may have existed before LUCA, they may not have had DNA, lipids, make proteins etc. but they died off and left LUCA o Maybe no, DNA, no RNA, no lipids, lots of branches of life o but they all died of except LUCA  Prokaryotes don't exist  o No single group of organism o Archaea and bacteria are not related o  Archaea is on the branch towards eukaryotes  Bacteria and archaea and totally different, they don't share anything in common o Pro means anteriority (before, earlier) o no evidence that prokaryotes came before eukaryotes o Suggests directionality: simple to complex... it is a misconception. Evolution does not always run in this direction o  there are lots of hypothesis of LUCA, LUCA might already been a eukaryotes   by reductive evolution, bacteria and archaea reduced the nuclear membrane  Bacteria may have gone through reductive evolution  o "Streamlining" to improve energy efficiency o Helps them reproduce faster e.g. Extremophiles  LUCA may have been a Proto-eukaryote  Stages of prebiotic evolution  o So what do you need? o  Abiotic synthesis   amino acids, macromolecules  Heritable information  Cells  Metabolism o Geophysical stage -> What was the composition of the Earth and atmosphere? o  can study the rock formation, know lots of information of the composition of Earth and atmosphere o Chemical stage -> How could the building blocks of life be synthesized? o  Miler-Urey experiment demonstrated macromolecules being synthesized in the conditions of the beginning of Earth o Biological stage -> How did the building blocks organize into living cells  We can find fossils to help understand the human evolution. However its harder to find fossils of the evolution of life and life happened billions of years ago  o Australopithecus afarensis was about 4 million years ago  Chemical stage  o Can one make organic molecules from inorganic molecules? o Miller-Urey experiment o Unanswered question: o  Development of polymers   DNA is a polymers  Proteins are polymers  he didn't produce the polymerized molecules  Chirality  Chirality  o Chirality..."handedness" o  cannot superimpose hands together o Two enantomers (optical isomers) o Same chemical and physical properties...But! o They have vastly different biological properties  Thalidomide  o Used as antiemetic drug in 1950s and 1960s o Teratogen: causes deformation of limbs o Antiemetic: prevents
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