Coacervate+Lab

=THE ROAD TO LIFE-FORMING COACERVATES=


 * Introduction / Background information**

Both scientists and philosophers have long pondered the origin of life on Earth. In ancient life it was believed that life could arise form inorganic, or non-living materials. Insects and frogs were thought to have formed from moist soil and maggots came from meat. While the world of scientists like Redi and Pasteur disproved the reality of spontaneous generation of life under present- day conditions. It is believe that the conditions of the primordial Earth may have allowed it to occur. This is the basis for A. I. Oparin’s heterotroph hypothesis for the origin of life. The heterotroph hypothesis shows how, under the right circumstances and given enough time, living cells could have formed from inorganic precursors.

When the Earth formed 4.6 billion years ago, it possessed conditions vastly different from today. The atmosphere consisted of hydrogen (which later escaped into space), methane, ammonia, and water vapor, and contained no free oxygen. The temperature was higher from greater volcanic activity, and the thinner atmosphere permitted large amounts of solar and ultraviolet radiation to reach the surface. Oparin proposed that under such high energy conditions, the abundant raw inorganic materials could be converted into simple organic compounds. This was proven by Stephen Miller in 1953. He created an apparatus to simulate conditions on the primordial Earth, and let it run for a week. At the end of the experiment, his “ocean” contained significant quantities of several low weight organic compounds, including several amino acids could, in this hot soup of organic compounds, polymerize into long chains of proteins. Internal interactions cause them to aggregate into organized clusters of organic molecules. Oparin termed these aggregates coacervates, and believed them to be primitive precursors of cells.

Coacervates, while not alive by any scientific definition, do exhibit some properties in common with living cells. Coacervates form a membrane of water around themselves. This membrane acts to control the effects of the external environment on the interior of the coacervate, just as the cell membranes acts. The membrane allows the coacervates to take up and concentrate substances inside of it, increasing it to many times the concentration outside the coacervate, greatly increasing the rate of chemical reactions within it. As the aggregates take up substances (or nutrients), they grow, and when they reach sufficient size they break off into smaller coacervates. Metabolism (control of an organism’s internal environment), absorption of nutrients, growth, and reproduction are all vital aspects of living things.

Oparin proposed that as coacervates became more complex they would carry on more lifelike functions. They would become heterotrophs, organisms with the ability to absorb nutrients from the environment for energy for growth. As the amount of nutrients in the environment decreased, competition for those precious resources increased. Heterotrophs with more complex biochemical reactions would have an advantage in this competition. Over time organisms would evolve that used photosynthesis to produce energy. The resulting release of oxygen and removal of free-floating nutrients would give rise to the conditions that prevent further spontaneous generation, but would allow for more advanced forms or organisms (aerobic organisms) to develop.

In this lab you will study the formation of coacervates formed from a mixture of a protein (gelatin) and a carbohydrate (gum Arabic). HCI will be used to promote the linking of the two organic compounds. The structure of the coacervates will be studied as well as its ability to absorb a substance from its surroundings and concentrated it (the substance being a methylene blue dye).

http://www.smithlifescience.com/MillersExp.htm http://www.simsoup.info/Origin_Landmarks_Oparin_Haldane.html http://www.mhhe.com/biosci/genbio/maderbio6e/outlines/ch20out.mhtml
 * Cross check the information at the following sites:**

Return to daily agenda Jan 13