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Unformatted text preview: MODULE 7 7a) Theories on the Origins of Life Introduction Where did life come from? How did life evolve? What are diff classes of microorganisms? How are these organisms related to each other? How does relatedness of organisms correspond to their physiological characteristics? What were earliest forms of life? What types of organisms were these? How did eukaryotes evolve? What is an evolutionary chronometer? Evolution of Earth and First Life Forms When earth formed 4.5 bya. no free oxygen, was reducing environment, other gases present were methane, ammonia, nitrogen and carbon dioxide First microorganisms around 3.9 bya At 3.5 bya, cyanoacterial microfossils (oxygenic photosynthesis) Between 2 and 1.5 bya, formation of oxygen atmosphere At 0.5 bya, burst of evolutionary activity (increase of types of organisms derived from existing ones) RNA form of life may be the precursor to modern cellular forms of life This theory based on knowledge of ribosomes, which are RNA molecules that can act as enzymes In modern organisms, RNA acts as intermediary btwn protein and DNA Protein in modern cells is associated with enzymatic activity and DNA is associated with genetic activity Early in earths evolution, molecules of RNA polymer developed ability to replicate, only purpose of these molecules was to make copies of selves, were not cellular in nature and did not have metabolism Eventually these molecules may have been captured by lipoprotein which evolved to become a membrane This theory suggests RNA may have been both a coding and a catalytic molecule There are number of modern ribosymes that play important part in cell metabolism Evolutionary experiments can be performed which select for mutants of ribosymes with altered enzymatic activity Translational system may have developed resulting in proteins which assumed catalytic functions Eventually DNA would replace RNA as coding molecule Other theories suggest life did not originate on our planet but in space Martian Meteor: rock found on earth originating from Mars, being examined for signs of life Theories suggest chemical signatures found on rock indicate it harboured living organisms Primitive Physiology First type of metabolism occurred under anoxic conditions (little or no oxygen)...
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This note was uploaded on 06/26/2011 for the course BIOL 140 taught by Professor Dr.joshneufeld during the Winter '10 term at Waterloo.
- Winter '10