Chemical Evolution
The central question of chemical evolution is how one can start with the simple chemical compounds that were lost likley present in the Earth's early atmosphere and oceans and wind up with organised, reproducing cell. This relatively new are of research is one im which we still have large gaps in our knowelege. Perhaps the most important experiment relating to chemical evolution happened in 1951 by Stanley Miller (b. 1930) and Harold Urey (1893–1981) at the University of Chicago. The novel apparatus of the Miller–Urey experiment is this:Based on analysis of gases that are released by volcanoes today scientists argue that the Earth's early atmosphere contained water vapor, hydrogen (H2), methane (CH4), and ammonia (NH3). Miller and Urey mixed these materials together in a large flask. Then, realizing that powerful lighting would have laced the turbulent atmosphere of the early Earth; they caused electric sparks to jump between electrodes in the flask. After a couple of weeks, they noticed that the liquid flask became cloudy and started to turn a brown color. Analysis revealed that this brownish liquid contained a large number of amino acids, one of the basic building blocks of life.
Thus, as early as the 1950s, experiments showed scientists that the modules of at least one of life's important molecules-proteins-might be generated by natural process in the oceans of the early Earth. Since that time, it has been found that energy sources such as ultraviolet radiation (from the sun) and heat (for example, from volcanoes will also produce amino acids. In subsequent experiments at the University of Chicago and other laboratories, scientists have used modified Miller-Urey devices to make other organic molecules, including lipids and bases, as well as complex substances such as long protein chains
PROTEINS: THE WORKSHORSES OF LIFE
The molecules we call proteins play many key roles in living systems. Some proteins from building materials which large structures are formed. Your hair, your fingernails, the tendons that hold your muscles in place, and much of the connective tissue that holds your body together, for example, are made primarily of protein molecules. Proteins also serve to regulate the movement of materials across cell walls, and thus control what goes into and out each cell in your body. In addition, proteins serve as enzymes, molecules that control the rate of complex chemical reactions in living materials.
Amino Acids: The Building Blocks of Proteins
Proteins are modular just like all complex biological molecules. They are made up of strings of basic building blocks called amino acids. All amino acids incorporate a characteristic backbone of atoms. One end terminates in a carboxyl group (COOH), a combination of carbon, oxygen, and hydrogen. On the other end is an amino acid group (NH2) nitrogen bonded to two-hydrogen atom. (These groups give this category of molecules their name.) Then between these two ends a carbon atom completes the backbone.
Branching off the central carbon atom is another atom or cluster of atoms-the “side group” that makes amino acids unique and interesting. Hundreds of different amino acids can be made in the laboratory, each with its different characteristic side group.
Two amino acids can bond together in a very simple way. The hydrogen (H) from the amino end will connect to the hydroxyl (OH). This water molecule moves off (you can think of this process as “squeezing out” the water), leaving the two amino acid bonded together in what is called a peptide bond. This process is identical to the condensation polymerization reaction that is often used to manufacture plastics and other polymers. Indeed, chemists often refer to a bonded chain of amino acids as polypeptide.
Once two amino acids have joined together with a peptide bond, more amino acids can be hooked onto either end by the same process to form a long string of amino acids. A protein is a large molecule formed by linking amino acids together in this way. There are many different amino acids to choose from, and different proteins correspond to a different ordering (as well as a different total number) of the amino acids in the string.
