How Eukaryotic Cell came into Life - Essay Example

Running head: How Eukaryotic Cell came into Life How Eukaryotic Cell came into Life [Institute’s How Eukaryotic Cell came into Life INTRODUCTION Living systems are any bodies that have the ability of interacting with the surroundings they are in. Flow of knowledge, energy and matter is required for their maintenance. Living systems can be unicellular or multi-cellular. As the name suggests, multi-cellular organisms are those made of more than one cell. There can be different kinds of cells, two of which are eukaryote and prokaryote cells. Prokaryotes had been first found around 3.5 billion years, which is just a billion years following the formation of the earth’s crust. Till today these life forms remain to be the most profuse ones, and since they have a very varied metabolism as compared to the eukaryotes, we can find a great many kinds of prokaryotic types. Since eukaryotic cells comprise of a huge majority of multi-cellular organisms and other complex cells, their origin has been considered a great highlight in the evolution of life. It is not really possible to determine when exactly these cells came into existence but according to Knoll (2006) it was around 1.6 – 2.1 billion years ago that eukaryotic cells took form. Certain acritarchs have been said to have originated 1650 million years ago and Grypania is an alga that was probably discovered to be approximately 2100 million years back. Besides this, it is the opinion of biomarkers that stem eukaryotes had come into being even before this and, as an example, steranes were found to be present in Australian shales almost 2.7 billion years ago. In 1966 the endosymbiosis theory was proposed by Lynn Margulis and he said that the prokaryotic cells and the initial eukaryotic cells lived together. At the beginning there was much hesitation in the acceptance of this theory. Eukaryote cells are more complicated and are set inside membranes while prokaryote cells do not have any membrane bound organelle. Another difference between these two cells is that eukaryotes have a cell nucleus while prokaryotes do not. This nucleus contains the DNA of the cell. Secondly, the size of eukaryotes is bigger as in the width and thus the volume is also more as compared to the prokaryotes. Chromosomes are present in eukaryotes which are actually where the DNA is. The movement of eukaryotes are controlled by motile cilia, also called flagella; and the flagella of eukaryotes are quite simple as compared to those in prokaryotes. Besides this, eukaryotes are like prokaryotes in respect to the plasma membrane and its function, but there is slight difference in the setup. Symbiosis as a mutually beneficial relationship happens when there are two species living together or closely for very long durations. This association is actually known as symbiotic, the word meaning to live together. Now there are different kinds of such a relationship and one is mutualism in which both the species get something out of the relationship. A very common example is that between plants and fungi. MAIN BODY Eukaryotes have been explained through various ways. An attempt has been made to explain the origin of these cells through the endosymbiotic theory as well, which was first proposed in 1905. This theory is basically concerned with the mitochondria, plastids and similar other organelles of the eukaryotes. This theory proposes that there were some specific kinds of organelles which actually came into being as free living bacteria. These were then taken within another cell as endosymbionts. Thus took place the development of cells and proteobacteria resulted in mitochondria while cyanobacteria lead to chloroplasts. In 1966 this theory was again proposed by Lynn Margulis and he said that the prokaryotic cells and the initial eukaryotic cells lived together. At the beginning there was much hesitation in the acceptance of this theory. Eukaryotes have double membranes around them. Within these membrane-bound compartments take place certain metabolic activities. As mentioned before, these cells have chromosomes. Chromosomes have a certain association with histone proteins, and are present within the nucleus and away from the cytoplasm. DNA may also be present in the organelles present in the eukaryotes, such as mitochondria. A lot of eukaryotes are ciliated with primary cilia that are extremely necessary from the processes of chemosensation, mechosensation and thermosensation. The compartments within the cells allow for proper and efficient functioning of the cells. Among the organelles present within eukaryotes the two important ones include mitochondria and chloroplasts. These have a vital part to play in the energy metabolism. Mitochondria have two membranes that are phospholipid bilayers containing proteins. The outer layer is smooth and the inner one has several folds which are known as cristae. The two layers serve the purpose of dividing the mitochondria into two different parts which are the intermembrane space and the mitochondrial matrix. Within the mitochondria are their own DNA, ribosomes and thus they are able to make proteins by themselves. Their DNA is circular. Following is a diagram of mitochondria: Chloroplast is found in plant cells. It is a tubular organelle containing a green pigment that is called the chlorophyll. There is a double membrane around a chloroplast and within it is contained a thick liquid called stroma. In the stroma are DNA, RNA, metabolites, and enzymes that are required for CO2 to be converted into organic substances. The stroma is separated from the thylakoids by the membranes of the thylakoid system. Grana is another part of chloroplast that are stacks of thylakoids. It is in thylakoids that chlorophyll is present. Following is a diagram of chloroplast: Among the different opinions and theories of the scientists regarding this topic, one is that long ago a prokaryotic cell ingested another small prokaryotic cell. It did not kill it, but rather benefited from the presence of the smaller cell. It continued to function within the larger cell and this served a purpose for it. As time passed these two cells merged and became dependent upon one another, thus developing a symbiotic relationship. One opinion is also that such ingested cells later on turned out to become the organelles which included the mitochondria and chloroplasts. There is also another theory regarding the origin and evolution of chloroplasts and mitochondria. There has been found a great deal of similarity between chloroplasts and bacteria and this similarity is what made the scientists think that there is a possibility of these two having evolved from the same organism: symbiotic bacteria, more particularly from cyanobacteria which are tiny organisms that harness light under oceans. Thus, mitochondria and chloroplasts are both descendants of bacteria and majority of the genes of the mitochondrial and chloroplast genomes have been transferred to the nucleus during the organelle’s evolution (Lewin, Krebs, Goldstein, & Kilpatrick, 2009, p. 114). The endosymbiotic origin of the chloroplast is emphasized by the relationships between its genes and their counterparts in bacteria. Now several biologists are of the opinion that the origin of mitochondria was from symbiotic aerobic bacteria. This opinion has been a result of the endosymbiosis model. The fact of the matter is that ancestral eukaryotic ingested the bacteria that turned into mitochondria. Prior to ingestion there were no enzymes for helping to use oxygen in respiration. Still, the ingested bacteria had the ability of performing such reactions and thus became the inner part of mitochondria. The mitochondria present inside a eukaryotic cell are a result of the division of the already present mitochondria together with the new bacteria being produced by means of cell division. The process used by mitochondria for division is simple fission, and they split into two, replicate and divide their circular DNA molecule in the same way as do bacteria. However, mitochondrial replication cannot take place (Biological Sciences Curriculum Study, 2002). Talking about chloroplasts now, these originated in evolution when a single celled organism engulfed a photosynthetic bacterium more than 1.5 billion years ago, and its descendants were passed from cell to cell and species to species as plants have lived and diversified over time. The relationship between the two organisms had actually been symbiotic, over evolutionary time the cyanobacterium passed on the majority of its genetic information to the host organism, and thus, in the process, lost the ability to survive independently of its partner (What makes a plant a plant?, 2011). Reference Biological Sciences Curriculum Study. (2002). BSCS Biology (9 ed.). Rutgers University Press. Lewin, B., Krebs, J. E., Goldstein, E. S., & Kilpatrick, S. T. (2009). Lewins genes 10 (10 ed.). Jones & Bartlett Learning. What makes a plant a plant? (2011, June 15). Retrieved November 15, 2011, from Science Daily: http://www.sciencedaily.com/releases/2011/06/110615142627.htm Read More