Life

Energy for life

All living beings need an energy source to activate chemical reactions. For example, to light a match requires some kind of energy source to trigger the reaction. In this case one simply has to rub the top on a rough surface to produce heat and make it light. This is a case of “activation energy”. Almost all the experiments we spoke about in the other chapters, used electric discharges, ultraviolet light and heat as energy sources. However these energy sources can be harmful to living molecules , because too much heat can disintegrate the molecules and the coacervate in them, causing irreparable damage. The primordial earth didn’t have a sufficiently thick and dense atmosphere, so ultraviolet radiations could have destroyed everything on the planet’s surface. This blocked the evolution of organisms in the areas struck by this energy. Both electric discharges and ultraviolet rays were generally active in the atmosphere , while life began almost certainly in the water or in protected humid places. Therefore, other forms of energy must have helped the beginning of life on Earth. As time passed, the diluted hot soup that was found in the depressions of the Planet’s surface, started to cool down and so the reactions become slower . At this point it is believed that new substances must have appeared which were able to help chemical reactions. These substances actually exist in every living organism: enzymes. Enzymes activate chemical reactions in living beings even at temperatures so low to be unable to supply the necessary energy to trigger them. Enzymes generally are formed by two parts: a protein part and a non protein part. The protein part includes the so called “active site”, meaning an area that adheres to the molecules on which it acts. The other non protein part, is often a vitamin and helps the protein part in its function. Enzymes can function also outside the living cell and this has been useful in multiple lab experiments. Today living beings tend to use sugars as a source of energy. Sugars or carbohydrates are molecules formed by carbon, oxygen and hydrogen and are synthesized by green plants. Did these substances exist in the primordial ocean? Melvin Calvin was able to answer this question with a new experiment. He struck different chemical compounds from those used in Miller’s experiments but which could have existed nonetheless in the primitive atmosphere, with high energy radiation. Thus, Calvin was able to obtain new molecules like simple sugars such as glucose. Thanks to specific enzymes, glucose and other similar sugars can create more complex structures such as starch and cellulose. Primordial oceans might have contained glucose molecules that could be usable as an energy source, but a lot of activation energy is needed to undo the ties among atoms of glucose and produce other energy. So presumably there was a similar mechanism to the one that happens in living beings nowadays, which means that they must bind some atoms to the molecule that must be divided so that they will attract electrons that will form a bond to weaken the molecular structure and break it down. In the case of glucose, the phosphorous groups (a group of phosphor, oxygen and hydrogen atoms) bind to a sugar molecule and transform it into glucose – phosphate, a weaker molecule than the initial one which consequently requires less activation energy to break down. ATP ( acid adenosyntriphosphate) is a chemical compound that supplies not only energy to add phosphoric groups to glucose, but also the necessary phosphoric group to weaken the molecule.