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NUCLEAR DNA

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  264

2026-08-13

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NUCLEAR DNA

Nuclear DNA has a geometric shape called a double helix. A helix is a spiral-shaped geometric figure. DNA looks like two helices wrapped around each other. Consider a ladder, made up of two poles held together by a series of rungs. Now consider taking the ladder at both ends and twisting it until it looks more like a spiral staircase—this is what the DNA molecule looks like. This is shown in Figure 11.1. The poles of the ladder are identical in all living things. They are made up of alternating sugar molecules (deoxyribose) and phosphates. Dangling off of each sugar molecule is one of four bases or nucleotides: adenine (A), guanine (G), cytosine (C), and thymine (T). When an adenine base and a thymine base comes into proximity, they form a bond to each other. Likewise, when cytosine and guanine get near each other, they will bond. Neither T nor A can link with G or C. The DNA molecule then, consists of the sugar phosphate backbones connected by linked base pairs and the linkages must be A–T, T–A, G–C, or C–G. Although base pairing is governed by the above rules, the order in which these pairs of with bases is the principle of genetics and inheritance. The order of the base pairs comprises a blueprint or genetic code that determines many of the characteristics of a person. An apt analogy would be one’s telephone number. Everyone has a ten-digit phone number but, in order to get your individual phone to ring, someone has to dial the digits in the correct sequence.