Lecture 19: Early History of Life PDF

Early History of Life Earth Formed 4.5 billion years ago Low oxygen levels, only anaerobic glycolysis possible Life appears quickly ○ Prokaryotes Atmospheric oxygen concentration ○ Little to none until bacteria evolved photosynthesis ○ 02 dissolved in water, reacted with iron = iron oxide ◆ Accumula...

Early History of Life Earth Formed 4.5 billion years ago Low oxygen levels, only anaerobic glycolysis possible Life appears quickly ○ Prokaryotes Atmospheric oxygen concentration ○ Little to none until bacteria evolved photosynthesis ○ 02 dissolved in water, reacted with iron = iron oxide ◆ Accumulated in alternating layers of red and dark rock = banded iron formation ◇ Evidence of earliest photosynthesis ○ 02 began to accumulate in atmosphere ◆ Cyanobacteria formed stromatolites ◇ Abundant in fossil record and are still formed in certain salty waters ◇ 02 released Cyanobacteria allowed evolution of oxidation reactions as energy source for ATP synthesis Prokaryotes Dominant life forms on earth 10X biomass of all eukaryotes Extreme metabolic diversity ○ Basis for all eukaryotic metabolism Began 3.8 billion years ago ○ Bacteria and archaea Cyanobacteria formed 2.8 billion years ago Classi cation = united by primitive similarities, 3 domains of life, endosymbiosis and LTG Prokaryotes vs. eukaryotes prokaryotes have ○ No nuclear envelope ○ No membrane bound organelles (only ribosomes) ○ Circular DNA, few genes in plasmids fi ○ No mitosis/meiosis, only binary ssion fi Lateral gene Transfer prokaryotes can horizontally generate transfer ○ Important for evolution Mechanisms ○ Transduction = genes via virus infection ○ Conjugation = plasmids from live bacteria ○ transformation = genes from environment (dead bacteria) Prokaryotic genome Chromosome ○ Small ○ Extreme diversity ○ Haploid ○ No sex ○ No centromere, chromatin Plasmids ○ Few genes ○ Independent replication and transcription ○ facilitates LGT Metabolism Energy and Carbon Energy ○ Phototrophs = use light ○ chemotrophs= use chemical compounds Carbon ○ Autotrophs = use CO2 ◆ photoautotrophs = energy = light, carbon = CO2 ◆ Chemoautotrophs = energy = inorganic, carbon= CO2 ○ Heterotrophs = use organic compounds they consume ◆ Photoheterotrophs = energy = light, carbon = organic compounds ◆ Chemoheterotrophs = energy and carbon = organic compounds Oxygen revolution 2.5 billion years ago Origin = Cyanobacteria ○ Increased O2 levels ○ O2 reactive - break bonds ○ Bad news for anaerobic organisms Allowed evolution of aerobic respiration ○ Greater yield of ATP Big Idea: Evolution is a Tinkerer 1. Production of ATP in aerobic respiration is borrowed from photosynthesis 2. Anaerobic origins in photosynthesis is apparent even in modern plants ○ plant productivity (50%) lost this way ○ Rubisco = most abundant protein in the world Archaea No peptoglycan in cell walls Unique lipids in cell membranes Inhibit extreme environments Methanogens ○ Important decomposers ◆ H2 to reduce CO2 to methane ◆ Anaerobic = O2 kills them halophiles ○ Thrive in water 10X salty as the ocean Thermophiles ○ 105 degree C Acidophilee ○ PH below 1.0 = battery acid is 1.0 Endosymbiosis Theory symbiosis is driving force behind evolution Secondary symbiosis ○ Heterotrophic protist engulfed algae contains plastids Metabolism Mitochondria ○ Aerobic prokaryotes Chloroplasts ○ From photosynthetic prokaryote