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Transcript
Origin of Eukaryotic Cells Earth is 4.6 byo Life originated 3.5– 4.0 bya Prokaryotes dominated earth for about 1by Cyanobacteria A type of prokaryote with much infolding of the cell membrane Capable of performing photosynthesis, which releases oxygen into the atmosphere Cyanobacterium heterocyst Oxygen atmosphere Oxygen begins to accumulate 2.7 bya evidence in banded iron in rocks (rusting) makes aerobic respiration possible Eukaryotes nearly all are aerobic, they depend on free oxygen to carry out their metabolic processes Accordingly, they could not have evolved before at least some free oxygen was present in the atmosphere Two processes are thought to have led to the origin of eukaryotes…. 1. Infoldings of the prokaryotic cell membrane 2. Endosymbiosis Development of internal membranes create internal micro-environments (“compartments”) advantage = increase efficiency ~2 bya infolding of the plasma membrane plasma membrane endoplasmic reticulum (ER) nuclear envelope *note double membrane nucleus DNA cell wall Prokaryotic cell Prokaryotic ancestor of eukaryotic cells plasma membrane Eukaryotic cell Write on a separate sheet of notebook paper to be turned in today Check-in #1: Given what you know about in folding and the cell membrane as a phospholipid bilayer: Why is the nuclear membrane a DOUBLE membrane (two layers of bilayer) REMEMBER: Two processes are thought to have led to the origin of eukaryotes…. 1. Infoldings of the prokaryotic cell membrane 2. Endosymbiosis Endosymbiosis FIRST early eukaryotic cells engulfed aerobic bacteria but did not digest them Led to the origin of mitochondria Mutually beneficial relationship internal membrane system aerobic bacterium mitochondrion Endosymbiosis Ancestral eukaryotic cell Eukaryotic cell with mitochondrion Endosymbiosis THEN eEarly eukaryotic cells engulfed Eukaryotic cell with mitochondrion photosynthetic bacteria but did not digest them Led to origin of chloroplasts mutually beneficial relationship chloroplast Endosymbiosis Eukaryotic cell with chloroplast & mitochondrion mitochondrion Endosymbiosis In this relationship one cell lived within the other, which is a special type of symbiosis called endosymbiosis in some cases of a symbiotic relationship, one symbiont cannot live independently of the other This may have been the case early symbiotic prokaryotes that became increasingly interdependent until the unit could exist only as a whole A model of the origin of eukaryotes Theory of Endosymbiosis Check in #2: How is the word “theory” in science different than the use of the word theory in every day language? Lynn Margulis Structural Evidence Both mitochondria & chloroplasts Resemble bacterial structure Are found in membranous envelopes (like a cell membrane) are the same approximate size as prokaryotes have 70s ribosomes Genetic Evidence Both mitochondria & chloroplasts have circular naked DNA DNA shares common sequences with modern prokaryotes Functional Evidence Both mitochondria & chloroplasts move freely within the cell reproduce independently from the cell through binary fission are inhibited by antibiotics Where Did Organelles Come From ? Membranous infoldings Nucleus ER Golgi Lysosomes Vesicles Endosymbiosis Mitochondria Chloroplasts Membrane infolding Endosymbiotic theory