Taking A Look At The Endosymbiotic Theory

This essay talks about endosymbiotic theory. Endosymbiotic means the event when an organism is living inside another organism. The theory explains how scientist believe eukaryotic cells developed. It states that the origin of eukaryotic cells is from prokaryotes. Mitochondria and plastids have similarities with bacteria, thus they differ from other organelles inside eukaryotic cells. The discovery of mitochondria being an exceptional cell organelle led Dr. Lynn Margulis to develop a theory of mitochondrial evolution. The theory of mitochondrial evolution, endosymbiosis, states that mitochondria and plastids have an extracellular origin. This essay focuses on endosymbiosis and its path from the discovery to theory, questioning if it is a theory

Scientist have stated that first prokaryotes, anaerobic bacteria have been around for approximately 3.8 billion years when in turn eukaryotes have been around for 1.5 million years. 1(Biology.iupui.edu, 2016) 49(Endosymbiosis, 2012) Prokaryotes are small, simple organelles witch do not contain a nucleus, but have naked DNA in the nucleoid. Bacteria belong to prokaryotes and anaerobic bacteria means bacteria which can grow in the absence of oxygen . Eukaryotic cells in turn are larger, complex organelles with a nucleus containing most of the cell’s DNA and it also consists of organelles, like mitochondria. 48(Cell Structures, 2012) The reason for prokaryotic anaerobic bacteria’s longer existence is lack of oxygen. When the first oxygen formed, some anaerobic bacteria evolved into aerobic bacteria. Aerobic bacteria means bacteria which requires oxygen in order to grow and survive51 2 (The Endosymbiotic Hypothesis, 2010) Endosymbiotic theory states that two free-living bacteria belonging to prokaryotes, aerobic bacteria and cyanobacterium were engulfed by another anaerobic cell. 3 This cell then became a host cell for the aerobic bacteria and the cyanobacterium witch essentially became the mitochondria and the plastids we know today. 49 (Endosymbiosis, 2012) Cyanobacterium stands for photosynthetic bacteria.52 --

Many scientist had noticed similarities between mitochondria and bacteria. This led observers in 1880s to form a hypothesis how modern eukaryotic cells have developed. This hypothesis was put aside. In 1950s Lynn Maguilis was observing how amoeba engulfed food and reproduced by dividing in two. At the same time she observed mitochondria and noticed how independently it worked inside the cell and how mitochondria’s way of reproducing was oddly similar to amoebas way to reproduce. 50 Before Lynn Margulis, Andres Schimper had studied the potential endosymbiotic nature in cells in 1883 and in 1905 his study was followed by Konstantin Mereschkowsky’s idea of plastids originating as endosymbionts. In addition Mereschkowsky was the first scientist to shape an idea of symbiogenesis and publiced a book Symbiogenesis and the origin of Species in collaboration with Ivan Wallin. 3 Wallin also played an important role in the formation of the hypothesis of eukaryotic cell development by being the first to suggest that eukaryotic cells are composed of microorganisms. These three scientists build a frame for Lynn Margulis,