Biology 102 Notes2 - Biology 102 Lecture 7 ORIGIN OF LIFE...

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Biology 102 Lecture 7: ORIGIN OF LIFE Understand how the conditions on Earth differed when life is assumed to have began: The ancient Earth differed because it consisted of mostly inorganic substances in the air and water, so O 2 was unavailable and if there was, life may have never started. Darwin’s Theory of Natural Selection suggests that all life on Earth is related to a common ancestral cell called Last universal common ancestor (LUCA). Know the 4 major steps associated with the origin of life: Inorganic compounds Monomers Polymers Protocell Cell Biological Evolution o Formation of monomers: The first step required for chemical evolution. They weren’t used not used in any way. They just sat there. Bacteria did NOT form them. Primordial Soup Hypothesis: The gases that were made up in Earth’s early atmosphere were strong reducing agents (donated electrons) because the atmosphere lacked oxygen. In an atmosphere that lacked O 2 , this reducing environment could have allowed for the formation of organic monomers in the presence of strong energy sources like heat from volcanoes or lightening from the sun. This hypothesis was tested by the Stanley-Miller Experiment. The energy source Miller used was an electric spark. Atmospheric gases were not oxidized (no O 2 ) and not decayed (no bacteria). They were washed into oceans and made the oceans thick and warm like soup. Iron Sulfur World Hypothesis: proposed that the first monomers were formed at the bottom of the ocean. Thermal Vents at the bottom of the ocean could provide all the needed elements and conditions. Iron and Nickel sulfide minerals could catalyze the formation of monomers from simple gases (Carbon monoxide, ammonia, and hydrogen sulfide) emitted from the vents. Extraterrestrial Origins Hypothesis: suggests that monomers come from another planet. Comets and meteorites pelted the earth’s surface for billions of years. o Formation of polymers: Monomers combined to form polymers with the aid of enzymes. This process is called polymerization. However, enzymes themselves are proteins, which was non-existent. Protein-first Hypothesis: Assumes that DNA (couldn’t have been first) arose after protein. Enzymes are needed to replicate DNA. Dry heat from the sun could have cause amino acids to polymerize into polypeptides, which could have been enzymatically active (acted like a protein). Therefore, the first polymers to form were proteins. RNA-First Hypothesis : RNA could have been first because it is the only macromolecule needed to progress to the first cell. RNA could be both a substrate (instructions) and an enzyme. Therefore, the first polymers to form were RNA.
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o Formation of protocell: An outer membrane arose before the true cell. Life requires chemical reactions to take place within a boundary. Cell membrane is required before the cell. Lipids tend to form from elements coming together. So the Protocell membrane had one fatty acid and the cell has two. Protocells are not alive. The internal and external environments differ. Simple responses to stimuli
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