Ch. 27- Evolution of Life

1. Ch. 27- Evolution of Life Ch. 27.1- Origin of Life

2. Target #1- I can describe the origin of the first cell • Earth is 4.6 billion years old • It existed as a lifeless planet for the first billion years • The origin of the first cell • Event was of low probability, but the amount of time allowed for the events to happen • Life arises from other life • The very first living cell came from inorganic chemicals • Reacted to form small organic molecules like glucose, amino acids, and nucleotides • Those small organic molecules polymeraized into macromolecules • Results in a protocell occurred after the formation of the first plasma membrane

3. Target #2- I can describe early Earth conditions • Early Earth Conditions • Ultraviolet radiation was intense • No ozone layer until single-celled organisms began to photosynthesize • Added oxygen to the atmosphere • Volcanoes erupted constantly • First atmospheric gases would have been methane, ammonia, and hydrogen • Early oceans formed from comet and meteorite impacts • As the water cycle first began, rain washed gases and minerals into the oceans • Frequent lightening and uncontrolled UV radiation would have allowed inorganic molecules to combine into the first organic molecules • Arose in either shallow pools, or in deep ocean vents

4. Miller-Urey Experiment • Early Earth simulation inorganic chemicals were placed into a closed system • Mixture was heated • Electric sparks were circulated • Simulated lightening • After 1 week, the solution contained a variety of amino acids and organic acids • Supports the hypothesis • Inorganic chemicals in the absence of oxygen and in the presence of a strong energy source can result in organic molecules Target #3- I can explain the Miller-Urey Experiment

5. Target #4- I can state the 3 hypothesis concerning the formation of macromolecules • There are three major hypotheses concerning the organic molecule to macromolecule stage • RNA-first hypothesis • Suggests that only RNA was needed at this time to progress toward formation of the first cell • RNA can be both genetic material and an enzyme • Known as a ribozyme • Protein-first hypothesis • Amino acids polymerize abiotically when exposed to dry heat • The heat of the sun caused proteinoids, small polypeptides, to form • When placed in water, proteinoids form microspheres, structures made only of proteins • Some proteins would have had enzymatic properties • Assumes that DNA came after protein enzymes arose • 3rd hypothesis- Graham Cairns-Smith Hypothesis • a combination of RNA- first and protein-first hypotheses • Thought that clay was helpful in polymerizing both proteins and nucleic acids • Clay is a type of soil that attracts small organic molecules and contains minerals like iron and zinc  served as catalysts

6. Protocell • After macromolecules formed, the plasma membrane would have coalesced to form a protocell • A structure that had a lipid-protein membrane and carried on energy metabolism • Key development because it separated genetic material from the outside environment • Would have used ATP for energy • Glycolysis, or a process similar to it, would likely have been taking place because of the lack of oxygen in early Earth’s atmosphere Target #5- I can describe a protocell

7. Heterotroph hypothesis • Heterotroph an organism that takes in preformed food • The ocean contained abundant nutrition small organic molecules • Suggests that heterotrophs preceded autotrophs Target #6- I can state the heterotroph hypothesis

8. Target #7- I can can explain how protocells may have evolved into true cells • True Cell a membrane-bound structure • A true cell can carry on protein synthesis to produce enzymes to allow DNA to replicate • Central Dogma of Molecular Biology • Information travels in one direction: DNA RNA Proteins • May not have applied to early cells • According to the RNA-first hypothesis, RNA would have been the first genetic material • Through reverse transcription, RNA could have helped to form DNA • Explains why some ancient particles, like viruses, or Archaea contain only RNA and not DNA • Once protocells acquired genes that could replicate, they became cells capable of reproducing, and biological evolution began