UNIT I BACKGROUND MATERIAL Forensic serology, if taken in its broadest sense to include them to standard texts, review articles, and so forth. Just as all aspects of the medico-legal examination of blood and detailed documentation was not in order for this unit, neither body fluids, draws its methods and the basis of its activities was complete treatment of the various disciplines. Topics for from a number of traditional intellectual disciplines. Fore- inclusion were selected on the basis of their relevance to most among these are biochemistry, immunology and forensic serological tests or methods. A few topics which are . genetics. not particularly relevant to medico-legal practice, have been This being a sourcebook, an effort has been made to pro- briefly discussed for the sake of completeness. vide background on the various methods and concepts dis- The material included in the background chapters is not cussed as they come up. As a result, many aspects of bio- regarded as being essential to the use of the succeeding units chemistry, genetics and immunology are discussed in con- of the Sourcebook. Cross references have been included, nection with the various procedures and tests which are used where relevant, however, so that readers who may wish to in forensic practice. Such an approach necessarily presents consult the background material on a particular subject in much of the material of a particular unified body of knowl- some context will be able to locate it without undue edge in a rather disjoint manner. Unit I has been included in difficulty. order to provide some background material in the unified Unit I consists of two sections, the first consisting of back- diiiplines in a more organized fashion. This treatment is ground material in biochemistry, immunology and genetics brief and topical. No effort has been made to provide de- and the second consisting of background material of various tailed documentation of the background material, for that selected methods which are widely used in forensic serology, approach would be the equivalent of preparing a sourcebook immunology and biochemistry. in one of these related fields. References are given, many of Background-Biochemistry Thomas Hunt Morgan 1866-1945 Courtesy National Library of Medicine -. -- - . Grcgor Mendel 1822-1 884 Courtesy National Library of Medicine . -. ules Bordet 1870- 196 1 PdEhrtich 1854-1915 Courtesy National Library of Medicine Courtesy National Library of Medicine 5 Background-Biochemistry SECTION l m BACKGROUND MATERIAL IN BIOCHEMISTRY, GENETICS AND IMMUNOLOGY and can vary in size from disaccharides (two monomeric units) to very large molecules (polysaccharides) like starch 1.1.1 Classes of biologically important organic compounds or glycogen. Different bonding arrangements between In this section, the structures of the major classes of com- monomeric units are possible. Bonds in which the Cl of one pounds of interest in biochemistry will be described. These unit is attached to the C4of the next are relatively common. are carbohydrates, lipids, amino acids and proteins and nu- These are called 1-4 linkages. If the C, (anomeric carbon) cleotides and nucleic acids. Vitamins and coenzymes could is in the a-configuration, the bond is called orl+4, while if it comprise another category, but will not be discussed in great is in the Dconfiguration, the bond is @l+configuration, the detail here. Some specialized types of molecules are dis- bond is D1+4. Figures 1.3 and 1.4 show maltose, which has cussed in other units, where germane. Porphyrins and hema- an a1+4 bond, and cellobiose, which has a B1+4. Both con- tin compounds, for instance, are discussed in section 4.1 sist of glucose units. Long chains may be formed too, such as 1.1.1.I. Carbohydrates. The carbohydrates are poly- that of amylose (Fig. 11.1). Branched polymers such as hydroxy aldehydes and ketones. The aldehydes are called amylopectin (Fig. 11.2) are possible, and are characterized by aldoses, and the simplest of these is glyceraldehyde, a three- a1+6 bonds at the branch points. carbon compound. There are four-, five-, six- and seven- 1.1.1.2 Lipids. The lipids are perhaps the most struc- carbon compounds as well. Dihydroxyacetone is the simplest turally diverse class of compounds. They are considered to- of the ketones, called ketoses, and there are likewise im- gether primarily on the basis of their solubility in organic portant four-, five- and six-carbon compounds in the group. solvents. As a class, lipids are nonpolar, hydrophobic materi- These simplest carbohydrates, called monosaccharides, als. The simple lipids are neutral triglycerides and waxes. often have one or more asymmetric carbon atoms, giving rise Triglycerides consist of glycerol, with three moles of to 2"stereoisomers, where n is the number of the asymmetric esterified fatty acid. The fatty acids are simple aliphatic carbon atoms in the molecule. With aldohexoses, for exam- organic acids, derived from alkanes or alkenes. They may be ple, where n = 4, there are 16 possible stereoisomers, 8 of saturated (having no double bonds in the chain) or un- which are mirror images of 8 others. The pairs of compounds saturated (one or more double bonds in the hydrocarbon which are mirror images are designated D- and L-, and the chain). The most important fatty acids are the C,, through sugars may be thought of as being derived from CZ0saturated compounds, the C16acid with a 9.10-double ~glyceraldehydein terms of absolute configuration. Simi- bond and the Ciaacids with either one, two or three double larly, the L-sugars may be thought of as being derived from bonds. The structure of a triglyceride is shown in Fig. 1.5. L-glyceraldehyde. The pseries of three-, four-, five- and Waxes are esters in which both the acid and the alcohol six-carbon sugars is shown in Fig. 1.1. Formulas used in this moieties have long hydrocarbon chains. figure are called Fisher projection formulas, and can ade- The more complex lipids may be phosphoglycerides, quately represent the D- and L-forms of the compounds. In sphingolipids, glycolipids, steroids or carotenoids. Phos- solution, however, glucose or any other sugar, may show pholipids are derivatives of phosphatidic acid (Fig. 1.6). The different behavior with respect to the rotation of plane polar- phosphoric acid residue may be esterified again to various ized light. This phenomenon comes about because the mole- compounds,as indicated in Fig. 1.7. The most common com- cule exists in solution as a cyclic hemiacetal, for which two pounds which are found as the "X" in Fig. 1.7 are glycerol, structures are possible. These are usually represented by inositol, ethanolamine, choline and serine. The compounds so-called Haworth formulas, as shown for glucose in thus formed are then called phosphatidyl glycerol, phos- Fig. 1.2. Aldohexoses normally form six membered rings phatidyl inositol, and so forth. These are actually classes of through a Cl-C5 interaction, while ketoses, such as fruc- compounds, since the fatty acid residues can vary. tose, form five membered rings through a G-% inter- Sphingolipids are those derived from sphingosine action. The C1which can have its hydroxyl group oriented (Fig. 1.8). An example is sphingomyelin (Fig. 1.9) which above or below the plane of the ring is called the anomeric occurs in nervous tissue. Glycolipids are compounds con- carbon. The two optically distinct forms, a- and @-, are sisting of carbohydrate and lipid moieties in covalent link- called anomers. The six-membered rings are termed pyra- age. They are very important in some animal cell membrane noses in systematic nomenclature, while the five-membered structures. Major classes of glycolipids are the cerebrosides rings are called furanoses, by analogy to pyran and furan. and the gangliosides. Complete hydrolysis of cerebrosides More complicated carbohydrates are, for the most part, yields sphingosine, one or two moles of fatty acid and a polymers of monosaccharides. They may be homopolymers, simple sugar, usually glucose or galactose. Gangliosides are Sourcebook in Forensic Serology, Imnology, and Biochemistry CHO I H-C-OH I CH20H CHO CHO I I HO-C-H H-C-OH I I H-C-OH H-C-OH I I CHzOH CHzOH CHO CHO CHO CHO I I I HO-C-H H-C-OH HO-C-H H-C-OH I I I I HO-C-H HO-C-H H-C-OH H-C-OH I I I I H-C-OH H-C-OH H-C-OH H-C-OH 1 I I I CH,OH CH,OH CHZOH CHIOH CHO CHO CHO CHO CHO CHO CHO CHO I I 1 I I 1 I 1 HO-C-H H-C-OH HO-C-H H-C-OH HO-C-H H-C-OH HO-C-H H-C-OH 1 I I I I I I I HO-C-H HO-C-H H-C-OH H-C-OH HO-C-H HO-C-H H-C-OH H-C-OH I I 1 I I I I I HO-C-H HO-C-H HO-C-H HO-C-H H-C-OH H-C-OH H-C-OH H-C-OH 1 I I I I I I I H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH I I I I 1 I I I CH,OH CHzOH CHzOH CHzOH CH20H CHzOH CHzOH CHZOH Figure 1.1 D - Series of aldoses Figure 1.2 Haworth formulas for the anomers of glucose OH OH Figure 1.5 A Triglyceride 0 Figure 1.3 Maltose II H2C - 0 - C - R, ~ ~ o r o ~ ~ H-C-0-C-R,$ I H 011 0 I II H2C - 0 - P - OH HO I 0- OH OH Figure 1.4 Cellobiose Figure 1.6 A phosphatic acid derivatives of cerebraides and contain a more complex car- given in the figure.