Biochemistry For Dummies. John T. Moore

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light, in which all the light waves vibrate in the same plane. When you use this kind of light, a chiral substance rotates the vibrational plane of the light — one form (the dextrorotatory, d, isomer) rotates the plane to the right, and the other (the levorotatory, l, isomer) rotates the plane to the left. The d and l forms are stereoisomers and are optically active.

      Illustrating the chiral compound: Fischer projection formulas

The chemist Emil Fischer developed a method of drawing a compound to illustrate which stereoisomer was present. These Fischer projection formulas are very useful in biochemistry. In a projection formula, a chiral carbon is placed in the center of a + pattern. The vertical lines (bonds) point away from the viewer, and the horizontal lines point toward the viewer (see Figure 3-9). Fischer used the D designation if the most important group (the group whose central atom had the highest atomic number) was to the right of the carbon, and the L designation if the most important group (again, the group whose central atom has the highest atomic number) was to the left of the carbon. Figure 3-10 shows two Fischer projection formulas.

      FIGURE 3-9: The construction of a Fischer projection.

      FIGURE 3-10: Fischer projection formulas distinguish stereoisomers.

      

The d and l symbols for chiral substance forms aren’t necessarily the Fischer projection formula’s D- and L- forms, respectively; thus, confusion may occur and lead to incorrect predictions. For this reason, the use of d and l is diminishing. The use of D and L is gradually being replaced by the R and S system of designating isomers. This system is particularly useful when more than one chiral carbon atom is present. For a description of this system, see Organic Chemistry For Dummies, by Arthur Winter (Wiley)

      Wow, that’s all the important organic chemistry you need for biochemistry in about 16 pages. How many pages did your organic chemistry text have, and what did it cost? This book is a real bargain!

Part 2

      The Meat of Biochemistry: Proteins

IN THIS PART …

      Building proteins with amino acids

      Putting the pieces together with amino acid sequencing and protein structures

      Playing stop-and-go with enzyme kinetics, using catalysts and inhibitors

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