| Creation Truth Outreach, Inc. Pamphlet |
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| Appendix A. Tutorial 3. Enzymes and Enzyme Shape In one sense a living cell is like a large factory, one in which energy is used to fabricate raw materials into various components and the components are then assembled into a useful product. In an efficient factory, a dedicated workstation is used for each component made. In comparison, a plant cell takes in raw materials such as minerals, air, nitrogen, and water. Sunlight provides the energy source. Then, a series of separate “work stations” use sunlight as an energy source in order to convert carbon dioxide from the air and water into sugars and starches. Other “work stations” convert other raw products into other materials. In such a cell, enzymes serve the equivalent of the workstations. Specialized enzymes control everything a cell does. Even the simplest cells capable of independent life need almost 2,000 unique, distinct kinds of enzymes in order to survive. Generally, the loss of any single one of these enzymes will either kill the cell or serious undermine its overall fitness. The only known functional purpose of the genetic code is to manage a cell’s enzymes. The genetic information in a cell tells the cell how to make the enzymes it needs to use, when to make them, and how to use them. So, life as we know it is enzyme-based. An enzyme is simply a long chain of amino acids. Very few enzymes are less than one hundred amino acids in length. Most are in the two hundred- to one thousand-amino acid range. The largest enzymes are over 1,000 amino acids in length. Normally, if the job for an enzyme is so complicated that its implementation would require much more than a thousand amino acids, then a cell will use an enzyme complex made of several smaller enzymes instead of a single huge one. Enzymes are formed by adding one amino acid onto the end of a chain of other amino acids. As the chain lengthens, the chain spontaneously folds into coils and sheets to produce a specific shape. Some of the 20 amino acids seem to promote coil formation. Others seem to promote sheet formation. Some amino acids like to be on the outside of an enzyme, next to the water in a cell. Other amino acids like to be on the inside of an enzyme, as far away from the water as they can get. The choice of amino acids used in the sequence making up a chain determines the shape that the enzyme forms. It is amazing to see just how precisely a huge, complicated combination of coils and sheets can form simply by using a proper sequence of amino acids. Perhaps a third of the amino acids in an enzyme are extremely critical. Normally, changing just one of these can completely change the shape of an enzyme. Perhaps another third are not so critical; a number of substitutions can be made without ruining a required shape. Perhaps another third are not very critical at all; a number of substitutions can be made to them without much impact at all. An enzyme’s shape determines how the enzyme functions. One typical enzyme function is two join two specific kinds of molecules to each other to form a new, third molecule. So, suppose a certain enzyme is needed to join together two different kinds of molecules for some function useful to a cell. Maybe combining the molecules are steps required to convert sugar into energy. Maybe combining them is needed to form a component to be used in decoding the genetic information of the cell. Maybe the product will become part of a cell membrane. There are lots of enzymes and lots of enzyme functions. We are simply showing one manner in which a typical one can work. Now, each of the two molecules that need to be joined will have a unique size, shape, and possibly electric charge. So, our enzyme then will have two sections in it. One section is shaped so that the first molecule fits into it, like a hand into a glove. As the various molecules in a cell bounce around, only the desired molecule fits. Then, when it happens to bang into the enzyme, the enzyme traps it and holds it. Likewise, the second section of the enzyme is shaped so that the second molecule fits into it, like a foot into a sock. As the various molecules in a cell bang into each other, eventually the enzyme will trap the second molecule. As soon as both molecules are trapped, they react with each other, forming some new, desired product. This is how an enzyme works. For us, the important thing is that this shows what we mean when we say enzyme shape is important. It is shape that allows it to snugly fit over a desired molecule (or atom such as iron or calcium) and attach to it. With even a slightly different shape, an intended molecule might not fit any longer, destroying the effectiveness of the enzyme. Equally bad, even if the desired molecule still fits, the shape might become so sloppy that other molecules also fit. This would ruin the selectivity of the enzyme and as a minimum, degrades its performance, and possibly ruining its effectiveness altogether. In order to construct a desired shape, enzymes are made of smaller structural units in the form of sheets and coils, which in turn are connected together by loops. A single chain of amino acids will fold into the specifically needed structure. |