A Plain English Map of the Human Glycolysis Enzymes

Abstract

T HIS paper presents a plain English map of the genes coding for the glycolysis enzymes in humans. It is designed to be used as a teaching tool to illustrate several important points. First, that every reaction in a cell requires an enzyme. Second, that every enzyme is a protein coded for by a gene somewhere on the chromosomes. Glycolysis is one of the most ancient and widely distributed biochemical pathways. It consists of 10 reactions, each catalyzed by a specific enzyme, and breaks one glucose molecule (containing 6 carbon atoms) into two molecules of pyruvic acid (containing 3 carbon atoms each). It occurs in the cytoplasm, does not require oxygen, and produces a net gain of 2 ATP and two molecules of NADH + H+ per glucose. If oxygen is present, the two pyruvic acid molecules enter the Krebs Cycle, producing the equivalent of 15 ATP each. If oxygen is not present, the pyruvic acid will accept the 2H from the NADH + H+ forming lactic acid in humans, or a variety of fermentation products such as alcohol or vinegar in other organisms. Each reaction of glycolysis requires an enzyme that, in turn, is coded for by a gene: This map shows one of the genes coding for each enzyme. Therefore, since there are 10 reactions, there are 10 genes on the map. The real story is somewhat more complicated and is explained in the notes to the genes. Some of these enzymes, such as triosephosphate isomerase, are, indeed, coded for by only one gene. Others, however, are coded for by several different, but similar, genes found at different places on the chromosome map. In such cases, the different genes are generally expressed in different tissues. For example, there are three different genes that code for aldolase, the fourth enzyme of the pathway. These have been mapped to chromosomes 10, 9 and 17. Each of the genes is expressed in specific tissues. Analysis of the amino acid sequences of these three enzymes shows that they are very similar to each other, thus implying that they all evolved from a single ancestral gene. The three forms of the aldolase