1.70 I(1.692) coo0 II(1.688) 39 II(1.671) Buoyant density FIGURE The buoyant density pattern of Drosophila virilus DNA centrifuged to equilibrium in neutral CsCl. Three prominent bands of satellite DNA(P=1.692, 1.688, and 1.671) are present, in addition to the main dna band (p=1.70) [After Gall, J.G., Cohen, E H, and Atherton, DD, Cold Spring Harbor Symp Quant. Bio/ 38, 417(1973)
(2)中度重复序列( moderately repeated sequence (3)单一序列( unique sequence)
（2）中度重复序列（moderately repeated sequence） （3）单一序列（unique sequence）
回文结构( palindromic structure) (1)回文结构 Palindrome TTAGCACGTGCTAA A ATCGTGCACGATT 回文结构也称反向重复( inverted repeats
2．回文结构（palindromic structure） (1) 回文结构 回文结构也称反向重复（inverted repeats）
(2)发夹形和十字形 TGCGATACTCATCGCA ACGCTACTCATAGCGT T 3 3 TGCGATGAGTATCGCA TAGCGT A AT Hairpin (a) 5 Fi ure Hairpins and cruciforms. Palindro- mic DNA (or RNA)sequences can form alternative G-C structures with intrastrand base pairing. When only a single DNA (or RNA)strand is involved it is called a hairpin(a). When both strands of a duplex DNA are involved, the structure is called a cruci- Cruciform form(b). Blue shading highlights asymmetric se (b) quences that can pair alternatively with a comple mentary sequence in the same or opposite strand
(2) 发夹形和十字形
五、RNA的结构 (一)RNA的类别 1.核糖体RNA( ribosomal rna,rRNA) 2.转移RNA( transfer rna,tRNA) 3.信使RNA( messenger RNA,mRNA)
（一）RNA的类别 1．核糖体RNA（ribosomal RNA, rRNA） 2．转移RNA（transfer RNA, tRNA） 3．信使RNA（messenger RNA, mRNA） 五、RNA的结构