Industrial production of amino acids by fermentation and chemo-enzymatic methods HOC YAY CO2H HO2C Figure 8. 1 Non-superimposable mirror images metric Such molecules result when the four groups attached to the carbon atom are all diffe arbon and a molecule of this kind is said to be asymmetric, or to contain an asymmetric car Molecules that are not superimposable on their mirror images are chiral. If two enantiomers compounds are related as non-superimposable mirror images, they are called enantiomers I cany you explain why the amino acid alanine is optically active, whereas glycine We can see from Table 8. 2 that the a-carbon of alanine is asymmetric (four different groups attached), whereas that of glycine is not. Optical activity requires an asymmetric carbon atom racemic If two enantiomers are mixed together in equal amounts the result is a racemic mixture mxtures We meet a number of enantiomeric items in daily life. The left hand, for example, is the mirror image of the right hand and they are not superimposable(see Figure 8.1). This becomes obvious if we try to put a right glove on a left hand. Similarly, a pair of shoes is an enantiomeric relationship while the stock in a shoe store constitutes a racemic mixture Representation of and the nomenclature for stereo-isomers are given in Appendix 8. 3. 1 Importance of chirality If we consider natural synthetic processes, enzymes are seen to exert complete control over the enantiomeric purity of biomolecules(see Figure 8.2). They are able to achieve this because they are made of single enantiomers of amino acids. The resulting enantiomer of the enzymes functions as a template for the synthesis of only one enantiomer of the product. Moreover, the interaction of an enzyme with the two enantiomers of a given substrate molecule will be different. Biologically important molecules often show effective activity as one enantiomer the other is at best ineffective or at worst detrimentalIndustrial production of amino acids by fermentation and chemo-enzymatic methods 237 I I Figure 8.1 Non-superimposable mirror images. Such molecules result when the four groups attached to the carbon atom are all different and a molecule of this kind is said to be asymmetric, or to contain an asymmetric carbon. Molecules that are not superimposable on their mirror images are chiral. If two compounds are related as non-superimposable mirror images, they are called Can you explain why the amino acid alanine is optically active, whereas glycine n is not (refer to Table 8.2)? We can see from Table 8.2 that the a-carbon of alanine is asymmetric (four different groups attached), whereas that of glycine is not. Optical activity requires an asymmetric carbon atom. If two enantiomers are mixed together in equal amounts the result is a racemic mixture. We meet a number of enantiomeric items in daily life. The left hand, for example, is the mirror image of the right hand and they are not superimposable (see Figure 8.1). This becomes obvious if we try to put a right glove on a left hand. Similarly, a pair of shoes is an enantiomeric relationship while the stock in a shoe store constitutes a racemic mixture. Representation of and the nomenclature for stereo-isomers are given in Appendix 1. 8.3.1 Importance of chirality If we consider natural synthetic processes, enzymes are seen to exert complete control over the enantiomeric purity of biomolecules (see Figure 8.2). They are able to achieve this because they are made of single enantiomers of amino acids. The resulting enantiomer of the enzymes functions as a template for the synthesis of only one enantiomer of the product. Moreover, the interaction of an enzyme with the two enantiomers of a given substrate molecule will be different. Biologically important molecules often show effective activity as one enantiomer, the other is at best ineffective or at worst detrimental. asymmetric carbon enantiomem enantiomers. racemic mixtures enantiomeric PJw