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Lecture 3

Lecture 3 Annotated

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Biological Sciences
Shelley A.Brunt

Slide 1Lecture 3Topic 2 continuedMicrobial Evolution and Diversityrelated readings chapter 4732014Brunt 20141 Slide 2Given the previous definitions the hypothesis is the first organismswere 732014Brunt 20142 Slide 3Hypotheseshypothesis the first cells were likely prokaryotic anaerobic and heterotrophic isdeductive reasoningfromall evidenceeukaryotic cell structure is relatively complexprokaryotic cell structure is relatively simplesimple most likely evolved before complexthere is good geological evidence that at the time the first celllike systems evolved the primitive Earth was anaerobic anoxic with reducing conditions and little tono free oxygenthe first organisms were likely anaerobiccells of most organisms contain several identical metabolic pathways that 1function in the absence of oxygen 2 use an organic form of carbonas a source of carbon skeletons for the synthesis of cell constituents and for energy heterotrophic metabolism eg glycolysis pathway eg glucosepyruvateapprox 9 stepsremember glycolysis can be an anaerobic pathway the first cell types were likely anaerobic and heterotrophic732014Brunt 20143Some evo biologists however thought that eukaryotic evolved before the prokaryotesOxygen existed but was not freely avaliable so first organisms were likeyly anoxic If you look at their metabolic activities there is one pathway that exists in all cells The glycolysis cycle is present in every type of cell and it is an anaerobic pathway The use of organic form of carbon would require a form of heterotrophic metabolism They couldnt have been autotrophic because we did not have free oxygen availbable and so the byproduct of heterotrophic organisms production is oxygen
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