1、 脱氧核苷酸的结构与种类脱氧核苷酸的结构与种类脱氧核苷酸脱氧核苷酸脱氧核苷脱氧核苷磷酸磷酸脱氧核糖脱氧核糖含氮碱基含氮碱基嘌呤嘌呤嘧啶嘧啶腺嘌呤腺嘌呤（A）鸟嘌呤鸟嘌呤（G）胞嘧啶胞嘧啶（C）胸腺嘧啶胸腺嘧啶（T）脱氧核苷酸种类脱氧核苷酸种类腺腺嘌呤嘌呤脱氧核苷酸脱氧核苷酸鸟鸟嘌呤嘌呤脱氧核苷酸脱氧核苷酸胞胞嘧啶嘧啶脱氧核苷酸脱氧核苷酸胸腺胸腺嘧啶嘧啶脱氧核苷酸脱氧核苷酸DNA的组成元素的组成元素脱氧核苷酸脱氧核苷酸规则的双螺旋结构规则的双螺旋结构1 DNA的结构的结构DNA的基本单位的基本单位DNA的多样性的多样性DNA的特异性的特异性碱基对的排列顺序千变万化碱基对的排列顺序千变万化特定的碱
2、基排列顺序特定的碱基排列顺序DNA的空间结构的空间结构C、H、O、N、PDNADNA的空间结构的空间结构-规则的双螺旋结构规则的双螺旋结构1.DNA分子是由两条反向平行的分子是由两条反向平行的脱氧核苷酸长链盘旋而成的规则脱氧核苷酸长链盘旋而成的规则双螺旋结构双螺旋结构2.脱氧核糖与磷酸交替连结，排脱氧核糖与磷酸交替连结，排列在外侧，构成基本骨架；碱基列在外侧，构成基本骨架；碱基排列在链的内侧。排列在链的内侧。3.两条链上的碱基通过氢键连结两条链上的碱基通过氢键连结起来，形成碱基对。碱基对的组起来，形成碱基对。碱基对的组成有特定的规律：即腺嘌呤一定成有特定的规律：即腺嘌呤一定与胸腺嘧啶配对，鸟嘌
3、呤一定同与胸腺嘧啶配对，鸟嘌呤一定同胞嘧啶配对。胞嘧啶配对。利用碱基互补配对规律的计算利用碱基互补配对规律的计算规律一规律一：DNA双链中的两条互补链的碱基相等，任意双链中的两条互补链的碱基相等，任意两个不互补的碱基之和恒等，占碱基总数的两个不互补的碱基之和恒等，占碱基总数的50%。即：即：A+GT+CA+CT+G50%，（A+G）/(T+C)(A+C)/(G+T)(T+C)/(A+G)1。规律二规律二：在：在DNA双链中的一条单链的双链中的一条单链的A+GT+C的值与的值与另一条互补链的另一条互补链的T+CA+G的值互为倒数关系。的值互为倒数关系。规律三规律三：DNA双链中，一条单链的双链中
4、，一条单链的A+TG+C的值与另的值与另一条互补链的一条互补链的A+TG+C的值是相等的，也与整个的值是相等的，也与整个DNA分子中的分子中的A+TG+C的值相等的值相等 。2.【例1】 (2000年广东高考题)已知一段双链DNA中碱基的对数和腺嘌呤的个数，能否知道这段DNA中4种碱基的比例和(A+C)：(T+G)的值( )A能 B否C只能知道(A+C)：(T+G)的值D只能知道四种碱基的比例 AATGC TACG已知腺嘌呤A的个数，等于已知T的数目(AT)。知道DNA中碱基对数，可以求出C+G的数目，也就可以求出G和C的数目(GC)。在双链DNA中，A+CT+G1。 【例2】 (1998年上
5、海高考题)在含有4种碱基的DNA区段中，有腺嘌呤a个，占该区段全部碱基的比例为b，则( )A b05 B b05C胞嘧啶为a（12b-1)个D胞嘧啶为b(12a-1)个C【解析】 根据碱基互补配对原则，有AT，CG，ATC TAGC，AaT，AA+T+C+Gba2a+G+CbG+Cab-2a，故GC12(ab-2a)a(12b-1)8oEU0gwM$8oDT+fvL!7nDT+euK#6mCS-euK#5lBR)dtJZ5lBQ(csIY4kAQ(csHX3jzP*brHX3iyO&aqGW2iyO&9pFV1hxN%9pFU0gwM$8oEU0gwL!7nDT+fvL!7mCS-euK#6m
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14、7nCS-euK#6mCS-etJZ5lBR)dtJZ4kAQ(csIY4kAQ*brHX3jzP*brGW2iyO&aqGW2ixN%9pFV1hxN%8oEU0gwM$8oEU+fvL!7nDT+fvK#6mCS-euK#6lBR)dtJZ5lBR)csIY4kAQ(csIX3jzP*brHX3jzO&aqGW2iyO&apFV1hxN%9pFV1gwM$8oEU0gwM!7nDT+fvL!7nDS-euK#6mCS-etJZ5lBR)dtJZ5kAQ(csIY4kAQ*brHX3jzP*brHW2iyO&aqGW2ixN%9pFV1hxN%8oEU0gwM$8oEU+fvL!7nDT+f
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16、P*brHX3jzP&aqGW2iyO&aqGV1hxN%9pFV1hwM$8oEU0gwM$8nDT+fvL!7nDT-euK#6mCS-euKZ5lBR)dtJZ5lAQ(csIY4kAQ(brHX3jzP*brHX2iyO&aqGW2iyN%9pFV1hxN%9pEU0gwM$8oEU0fvL!7nDT+fvL!6mCS-euK#6mCR)dtJZ5lBR)dtIY4kAQ(csIY4jzP*brHX3jzP*aqGW2iyO&aqGV1hxN%9pFV1hxM$8oEU0gwM$8nDT+fvL!7nDT-euK#6mCS-euKZ5lBR)dtJZ5lAQ(csIY4kAQ(crHX
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