Page - (000018) - in Biomedical Chemistry: Current Trends and Developments

Diana C. G. A. Pinto, João M. P. Pereira, Artur M. S. Silva* 1.1 Functional Groups of Biomolecules and their Reactions Abstract: This chapter starts with a general introduction on some concepts needed to understand the reactivity of organic functional groups. Elementary reaction mechanisms are then presented according to their functionality with relevant biological examples. These reactions explain the vast majority of transformations involving biomolecules. Finally, two examples on the application of the presented concepts are given, namely the metabolism of fatty acids and reactivity of penicillin. Both of these examples call for various types of reactions showing the diversity and simplicity of biological transformations when analysed step by step. 1.1.1 Functional Groups in Biological Systems The main definition of a functional group in organic chemistry books is as a chemically reactive group of atoms within a molecule that contribute to its characteristic reactivity. Functionality is usually regarded as “implying the presence of heteroatoms and/or unsaturation, but it would not be helpful to attempt to define precisely the limits of application of the term” (IUPAC, Commission on Nomenclature of Organic Chemistry, 1993). Functional group reactivity may be changed by the presence of other neighbouring functional groups but usually behaves uniformly in every molecule where it can be found. There are several common functional groups that are related to families of organic compounds according to their structural features. However, from those functional groups only a few are found in biological systems (Table 1.1.1). The types of bonding found in these functional groups may be explained by the existence of various hybrid atomic orbitals of the carbon atom created from combination of the one 2s and the three 2p orbitals (Table 1.1.2).