|The First Cell|
Before going in depth about the formation of the first cell, it must be first understood what cells are. All life is formed by cells. What makes organisms different, is how many cells there are, what type of cells there are, and how these cells are organized. Many micro-organisms consist of only one cell, which carries out all functions needed to survive. Other organisms consist of more cells, such as humans, who contain over a trillion cells, most of which are specialized for a certain function.
Every cells is made up of many smaller parts. There is the nucleus present in most cells, which contains DNA (deoxyribonucleic acid), which stores the blueprint of the cell. There are mitochondria which break down compounds and produce energy. There are many other parts in a cell, each of which has a specific function. These parts of the cell are made up of proteins, which are made up of long strands of amino acids, which are made up of different combinations of the base elements of carbon (C), hydrogen (H), nitrogen (N), and oxygen (O). Of all the possible types of combinations forming amino acids, only 20 are used in proteins. However, these 20 amino acids can form almost infinite numbers of combinations to create an almost infinite number of proteins.
But how was the first cell created? Charles Darwin proposed that the first proteins evolved from non-living matter. But how did this happen? Firstly, the earth was not the same today as it was 3 to 4 billion years ago when the first organic compounds where being formed. The early atmosphere was too hot for oxygen (O), nitrogen (N), and other elements to exist alone, as they do today. These elements combined to form methane (CH4), ammonia (NH3), water vapor (H2O), hydrogen sulfide (formula), hydrogen molecules (H2), etc. These where all, and thus the early atmosphere was called a 'reducing atmosphere'. Further, as there was no free oxygen to form an ozone (O3) layer to protect the earth from the harsh ultra-violet radiation (UV Rays) from the sun. Also, there where incredibly violent electrical storms, which where more violent than any which occur today.
In 1924 Alexander Oparin hypothesized that organic compounds where formed in the early earth when the high energy provided by UV Rays, and storms, caused different molecules to react, and create new organic compounds, such as Amino Acids DNA, and RNA.
In the early 1950s, Professor Harold Urey and one of his students, Stanley Miller, began experimenting to prove Oparin's theory. Miller built an apparatus which circulated gasses likely to be present in the early atmosphere (Methane (CH4), Ammonia (NH3), Water (H2O), and hydrogen (H2) ) past an electrical discharge, simulating the UV Rays and violent electrical storms present in the early atmosphere.
After allowing the experiment to continue for a week, the results where startling. The previously colorless solution inside the apparatus had turned red. Upon analyzing the solution, Miller found many organic molecules present, some of which couldn't be readily identified. The most important of created compounds, however, where amino acids. This, in effect, proved Oparin's theory that organic compounds could have been created in the early atmosphere. Further studies showed that some amino acids would have combined with hydrogen cyanide (HCN), which is a byproduct of volcanic activity. This combination would form purines and pyrinidines, which are used to make nucleic acids, which in turn create DNA
After these compounds had been created on the early earth, the earth eventually began to cool. Water vapor the condensed, which formed vast oceans, seas and lakes, in which simple organic molecules began to accumulate for millions of years, producing an "organic soup" of sorts. The amino acids would have then polymerized (which means they formed chains, such as proteins. E.g... (aa=amino acid) aa-aa-aa-aa-aa = protein). The most likely theory as to how the amino acids combined is that they where washed up into clay/rock depressions on land, where the water evaporated, leaving behind concentrated organic compounds in high heat.
Sidney W. Fox set out to prove this. He took a mixture of approximately 20 different amino acids, and heated then to the melting point. When they cooled, Fox observed that they had polymerized into proteins.
But how did these proteins and other organic compounds form the first cell? It is not very clear, but most likely, a group of organic molecules including proteins, and primitive fatty acids formed into a droplet, or bubble-like structure, which had the ability to combine with external elements, such as proteins not a part of it. Eventually, these droplets would grow, and divide. These droplets would eventually evolve into the first true cell. These early cells would have been autotrophs, which are organism which produce their own energy, usually from sunlight. Some of these cells would then evolve into heterotrophs (organisms which ingest organic material as a nutrient source)Next: Evolution of Life
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