二、突变产生的机理 (b) standard and anomalous base Standard base- pairing arrangements pairing arrangements occur if bases are in the rare tautomeric forms. Base Th mine (common formy Adenine(common form) mispairings due to tautomeric shifts were originally thought to be a major H一N source of errors in replication, but Cytosine(common form) Guanine(common form) such structures have not been Anomalous base pairing arrangements detected in dna and most evidence 一H·非市NA now suggests that other types of anomalous pairings are responsible 看非音看H for replication errors A Thymine(common form Guanine (rare form) Genetics Ch12.11
Genetics Ch12.11 二、突变产生的机理 • (b) Standard and anomalous basepairing arrangements occur if bases are in the rare tautomeric forms. Base mispairings due to tautomeric shifts were originally thought to be a major source of errors in replication, but such structures have not been detected in DNA, and most evidence now suggests that other types of anomalous pairings are responsible for replication errors
突变产生的机理 ·2.碱基类似物( base analogues):是在化学结构上与 DNA的碱基很相似的物质,在DNA复制时,“冒充”碱 基掺入到DNA链中去。 ·例如:5-溴尿嘧啶(BU)是胸腺嘧啶(T)的结构类似 物。当细菌在BU中培养时,T被BU取代,与A配对。 BU的酮式结构兮BU的烯醇式结构 (与A配对)多(与G配对)少 造成AT→GC(多)GC→AT(少)(转换) 其他化合物:5-氯(氟)尿嘧啶,2-氨基嘌呤 A Genetics Ch1212
Genetics Ch12.12 二、突变产生的机理 • 2．碱基类似物（base analogues）：是在化学结构上与 DNA的碱基很相似的物质，在DNA复制时，“冒充”碱 基掺入到DNA链中去。 • 例如：5-溴尿嘧啶（BU）是胸腺嘧啶（T）的结构类似 物。当细菌在BU中培养时，T被BU取代，与A配对。 • BU的酮式结构 BU的烯醇式结构 （与A配对）多 （与G配对）少 • 造成 AT → GC（多） GC → AT（少） （转换） • 其他化合物：5-氯（氟）尿嘧啶，2-氨基嘌呤
突变产生的机理 5-Bromouracil(a base analog resembles thymine, except that it has a bromine atom in place of a Normal base Base analog H3C methyl group on the 5-carbon atom. Because of the similarity in H TN一H H-《B LN一H their structures 5-bromouracil may be incorporated into dna in place of thymine. Like thymine, 5- Thymine bromouracil normally pairs with 5-Bromouracil adenine but, when ionized, it may pair with guanine through wobble. A Genetics ch1213
Genetics Ch12.13 二、突变产生的机理 • 5-Bromouracil (a base analog) resembles thymine, except that it has a bromine atom in place of a methyl group on the 5-carbon atom. Because of the similarity in their structures, 5-bromouracil may be incorporated into DNA in place of thymine. Like thymine, 5- bromouracil normally pairs with adenine but, when ionized, it may pair with guanine through wobble
突变产生的机理 Normal pairing Mispairing H Br UN一H H-Bu H一NG 5-Bromouracil Adenine 5-Bromouracil (ionized Guanine 5-Bromouracil(a base analog) resembles thymine, except that it has a bromine atom in place of a methyl group on the 5-carbon atom. Because of the similarity in their structures, 5-bromouracil may be incorporated into DNain place of thymine. like thymine, 5 bromouracil normally pairs with adenine but, when ionized, it may pair with guanine through wobble. A Genetics Ch1214
Genetics Ch12.14 二、突变产生的机理 • 5-Bromouracil (a base analog) resembles thymine, except that it has a bromine atom in place of a methyl group on the 5-carbon atom. Because of the similarity in their structures, 5-bromouracil may be incorporated into DNA in place of thymine. Like thymine, 5- bromouracil normally pairs with adenine but, when ionized, it may pair with guanine through wobble
突变产生的机理 ·3.亚硝酸(HNO2):具有氧化脱氨的作用。 A脱H次黄嘌呤)→H-C→AT→GC C-脱氦U尿嘧啶)→U-A→GC→AT H一N Nitrous acid C (HNO,) H-UN-H·NA CG N Cytosine Uracil Adenine (A Genetics ch1215
Genetics Ch12.15 二、突变产生的机理 • 3．亚硝酸（HNO2）：具有氧化脱氨的作用。 A H H C AT GC C U U A GC AT ⎯⎯⎯→ − → ⎯⎯⎯→ − → 脱氨 脱氨 （次黄嘌呤） （尿嘧啶）