Chapter 4 Animal Genome,Gene and DNA
第四章 动物基因组：基因和 DNA
? Nucleic acids are genetic
materials核酸是遗传物质
? Structure of nucleic acids核
酸的结构
? Synthesis of nucleic acids核酸
的合成
? Gene structure基因结构
? Variations of gene and DNA
基因和 DNA的变异
? Translation,synthesis of
protein 蛋白质的合成 --翻译
Nucleic acids are genetic materials
核酸是遗传物质
Chromosome
染色体
protein蛋白质
DNA
RNA
Which one is genetic material?
哪一个 是遗传物质？
Experiments prove that DNA is
the molecule of heredity
? Transformation experiment with
pneumonia
? Transfection experiment with
bacteriophage
? Experiment with tabauo mosaic virus
(TMV)
Transformation experiment
肺炎球菌的转化实验
无毒的 RII肺炎
球菌（小的）由被杀
死的 SIII （大的）的
DNA转化成有毒的肺
炎球菌
Streptococus pneumoniae
肺炎球菌
? S型：多糖组成荚膜，分 SI,SII,SIII
? R型：无荚膜，分 RI,RII,RIII
Transformation
experiment with
pneumonia
肺炎球菌感染小
鼠实验
象加热杀死的 SIII能使不致
病的 RII变成能致病的 SIII,这种
现象叫转化 （ transformation）
把 SIII死菌中能转化 RII的物质叫
转化因子
证明转化因子
是 DNA的实验
A diagram of the experiment that
demonstrated that DNA is the active
material in bacterial transformation
Transfection experiment with bacteriophage T2
T2噬菌体的侵染实验 (I)
T2噬菌体的侵染实验 (II)
Experiment with tabauo mosaic virus (TMV)
烟草花叶病毒感染试验
Key points,The genetic information of living
organisms is stored in deoxyriboncleic acid
(DNA),In some viruses,ribonucleic acid
(RNA) is the genetic material
Nucleic acids
核酸
脱氧核糖核酸
(DNA)
核糖核酸
(RNA)
Structure of nucleic acids
核酸的结构
Size of genome基因组大小
Phylum Species Genome (bp)
Algae Pyrenomas salina 6.6× 105
Mycoplasma M.pneumoniae 1.0 × 106
Bacterium E.coli 4.2 × 106
Yeast S,cerevisiae 1.3 × 107
Slime mold D,discoideum 5.4 × 107
Nematode C,elegans 8.0 × 107
Insect D,Melanogaster 1.4 × 108
Bird G,domesticus 1.2 × 109
Amphibian X,laevis 3.1 × 109
Mammal H,sapiens 3.3 × 109
Nucleic acids are macromolecules composed
of repeating subunits called nucleotides,Each
nucleotide is composed of (1) a phosphate
group,(2) a five-carbon sugar (pentose),and (3)
a cyclic nitrogen-containing compound called a
base.
DNA的基本组成单位是 脱氧核苷酸。每个脱氧核苷
酸含有一个碱基，一个脱氧核糖和一个磷酸基。
碱
基
结
构
式
Chargaff法则
? 腺嘌呤与胸腺嘧啶的克分子数相等,A”=“T”
? 鸟嘌呤与胞嘧啶的克分子数相等,G”=“C”
The Watson-Crick double-helix
DNA双螺旋结构模型要点
? DNA usually exists as double helix,with the two
strands held together by hydrogen bonds
between the complementary bases,A paired
with T and G paired with C.
DNA分子是由两条同轴反向互相缠绕的多核甘酸链组成
的双螺旋结构
? 糖和磷酸排在外面构成骨架,两链相应的核甘酸的碱基
互相配对由氢键连接排列在内侧
? The base pairs in DNA are stacked about 0.34
nm apart,with 10 base pairs per turn (360゜ ) of
the double helix
双螺旋直径为 20A，螺距为 34A,包含 10对碱基
糖 -磷酸基团骨架
（黑色）以及碱基
（彩色）
DNA双螺旋横断面
RNA 的基本结构单位是核苷酸，它由
含氮碱基（ A,G,C,U），核糖和磷酸
基构成 。
Structure of RNA
含氮碱基（ A,G,C,U）和核酸
RNA的分类
? mRNA,冒子结构和尾巴
? tRNA：三叶草结构
? rRNA：大亚基和小亚基
Key points
? Nucleic acids are of two types,DNA and RNA
? DNA usually exists as double helix,with the two
strands held together by hydrogen bonds between
the complementary bases,A paired with T and G
paired with C
? The complementarity of the two strands of a double
helix makes DNA uniquely suited to store and
transmit genetic information from generation to
generation
? The two strands of a double helix have opposite
chemical polarity
? RNA usually exists as a single-stranded molecule
Testing your knowledge
? The E.coli virus ΦX174 stores its genetic information in
single-stranded DNA,When DNA was extracted from
ΦX174 virus particles and analyzed,21 percent of the
bases were found to be G residues,From this information,
can you determine what percentage of the bases in this
DNA were thymine residues? If so,what percentage? If
not,why not?
Synthesis of nucleic acids
核酸的合成
? DNA合成 复制 自体催化
? RNA合成 转录 异体催化
? Watson and Crick提出 半保留复制的设
想。如何论证？
Semi-conservative replication
DNA半保留复制 —CsCl2梯度离心
A.离心图带 B.扫描图
The diagram of CsCl2 density-
gradient centrifugation
CsCl2梯度离心示意图
Semi-conservative
replication
Synthesis
复制进行
The process of DNA synthesis
DNA复制过程
Initiation
复制起始
复制起始（ unwinding DNA双
螺旋解开 ）
? Helicases 解旋酶
? DNA-Binding Protein单链结合蛋白
（ SSB）
? Topoisomerases 拓朴异构酶
复制进行
在 RNA酶催化下，以 DNA为模板，
合成一小段 RNA作为引物，然后在
DNA聚合酶 III催化下，以脱氧核糖
核苷三磷酸（ dATP,dGTP,dTTP、
dCTP）为底物，以 DNA的两条单链
为模板合成与母链互补的子链。
Synthesis direction 合成方向
5’ 3’
Continuous synthesis of one strand;
Discontinuous synthesis of the other strand
(Okazaki fragment 冈崎片段 )
Leader strand前导链,3’ 5’
Lagging strand后随链,5’ 3’
Transcription 转录
这是以 DNA为模板，在依赖 DNA
的 RNA聚合酶作用下合成 RNA的过程。
RNA聚合酶的构成
α 亚基
β 亚基
β` 亚基
σ 亚基
核心酶
Nonsense chain,the chain is not transcripted
无意义链,没被转录的其中一条链
Sense chain,the chain is transcripted
有意义链,被转录的其中一条链
Key points
? DNA replication is complex,requiring the
participation of a large number of proteins
? DNA synthesis is continuous on the progeny
strand that is being extended in the overall 5’ 3’
direction,but discontinuous on the strand
growing in the overall 3’ 5’ direction
? New DNA chains are initiated by short RNA
primers synthesized by DNA primase
Gene structure基因结构
? Evolution of the concept of the gene,
summary
? Evolution of the concept of the gene,
function
? Evolution of the concept of the gene,
structure
? A genetic definition of the gene
? Complex gene-protein relationships
Evolution of the concept of the gene,summary
Gene structure
(a) Typical prokaryotic gene
(b)Typical eukaryotic gene
Gene structure
The concept of the gene has undergone many
refinements since its discovery by Mendel in 1866,
Most genes encode one polypeptide and can be
operationally defined by the complementation test.
Evolution of the concept of the gene,function
? Mendel,constant factors controlling phenotypic
traits
? Garrod,one mutant gene-one metabolic block
? Early evidence that enzymes are controlled by
genes
? Beadle and Tatum,One gene-one enzyme
? One gene-one polypeptide
Mendel,constant factors controlling
phenotypic traits
Garrod,one
mutant gene-one
metabolic block
Early evidence that
enzymes are
controlled by genes
Beadle and Tatum,
One gene-one enzyme
One gene-one polypeptide
The existence of a basic genetic element,
that controlled a specific phenotypic trait was
established by Mendel’s work in 1866,Since
the discovery of Mendel’s results in 1900,the
concept of the gene has evolved from unit that
can mutate to cause a specific block in meta-
bolism,to the unit specifying one enzyme,to
the sequence of nucleotide pairs in DNA encoding
one polypeptide chain.
Evolution of the concept of the gene,
structure
? The pre-1940 Beads-on-a-string concept
? Discovery of recombination within the
gene
? Recombination between adjacent
nucleotide pairs
? Colinearity between the coding sequence
of a gene and its polypeptide product
The concept of the gene has evolved
from a bead on a string,not divisible by
recombination or mutation,to a sequence
of nucleotide pairs in DNA encoding one
polypeptide chain,The unit of genetic
material not divisible by recombination or
mutation is the single nucleotide pair.
A genetic definition of the gene
? The complementation test as an
operational definition of the gene
? Intragenic complementation
? Limitations on the use of the
complementation test
The complementation test as an
operational definition of the gene
The arrangement of
genetic markers in
cis and trans hetero-
zygotes
The complementation test as an
operational definition of the gene
The cis-trans
position effect
The complementation test as an
operational definition of the gene
The cis test
The complementation test as an
operational definition of the gene
The trans test
Intragenic
complementation
Intragenic complementation
may occur when a protein is
a multimer containing at least
two copies of one gene product
Limitations on the use of the
complementation test
The complementation or trans test provides an
operational definition of the gene; it is used to
determine whether mutations are in the same gene
or different genes,Intragenic complementation
may occur when a protein is a multimer containing
at least two copies of one gene product.
Complex gene-protein relationships
? Alternate pathways of transcript
splicing,protein isoforms
? Assembly of genes during
development,human antibody
Alternate pathways of transcript
splicing,protein isoforms
Testing your knowledge
? The red alga Polyides rotundus stores its genetic
information in double-stranded DNA,When DNA
was extracted from P,rotundus cells and analyzed,
32 percent of the bases were found to be guanine
residues,From this information,can you determine
what percentage of the bases in the this DNA were
thymine residues? If so,what percentage? If not,
why not?
Variations of gene and DNA
基因和 DNA的变异
? Mutation and its basic features
基因突变及其特性
? The molecular basis of mutation
基因突变的分子基础
? DNA repair mechanisms
DNA损伤的修复
Mutation and its basic features
基因突变及其特性
? The term mutation refers to both (1) the change in the
genetic material and (2) the process by which the change
occurs,Today,the term mutation often is used in a
narrow sense to refer only to changes occurring within
genes 基因突变就是一个基因变为它的等位基因
? Mutation’s features基因突变的特性
? Mutation is a reversible process可逆性
? Multiple directions多方向性
? Low frequencies低频率性
The molecular basis of mutation
基因突变的分子基础
? Mutation types基因突变类型
? Effects of base substitution on
phenotypes 碱基置换突变的结果
? Mutation mechanism基因突变的机制
Mutation types基因突变类型
? Base substitution 碱基置换突变
? Transitions,嘌呤 嘌呤；嘧啶 嘧啶
? Transversions,嘌呤 嘧啶
? Frameshift mutations移码突变
? Deletion and addition of short fragments
片段突变
Effects of base substitution on
phenotypes 碱基置换突变的结果
? synonymous mutation同义突变
? non-synonymous mutation错义突变
? non-sense mutation无义突变
Mutation mechanism
基因突变的机制
? Mutations induced by chemicals
? 碱基类似物的诱发突变
? 改变 DNA化学结构的诱变剂
? 结合到 DNA上的诱变剂
? Mutations induced by radiation
? Mutations induced by transposable
genetic elements
The mutagenic base analogs
碱基类似物的诱发突变
5’-溴尿嘧啶
5-bromouracil
酮式：与 A配对
烯醇式：与 G配对
改变 DNA化学结构的诱变剂
A H,H-C亚硝酸
G mG,mG-T烷化剂
结合到 DNA上的诱变剂
? 吖 啶类化合物能结合到 DNA上，插入碱
基之间使它们分开，造成不等交换
? 吖 啶类化合物还能使 DNA分子插入一个
碱基或丢失一个碱基，产生移码突变
Mutations are induced by chemicals,ionizing
irradiation,ultraviolet light,and endogenous
transposable genetic elements that jump from one
position in the genome to new sites,Point mutations
are of three types,(1) transitions,purine for purine
and pyrimidine for pyrimidine substitutions,(2)
transversions,purine for pyrimidine and pyrimidine
for purine substitution,and (3) frameshift mutations,
additions or deletions of one or two nucleotide
pairs,which alter the reading frame of the gene
distal to the site of the mutation,Several inherited
human diseases are caused by expanded
trinucleotide repeats.
DNA损伤的修复（自学）
? 紫外线对 DNA的损伤
? 光复活作用
? 切除修复
? 重组修复
Translation:synthesis of protein
蛋白质的合成 ——翻译
DNA mRNA 蛋白质
核苷酸 氨基酸
核苷酸 氨基酸
Nucleotide Amino acid
Genetic code 遗传密码
Important properties of genetic codes
o The genetic code is composed of nucleotide
triplets三联体
o The genetic code is degenerate兼并性
o The genetic code is comma-free连续性
o The genetic code is nonoverlapping
o The genetic code is nearly universal通用性
o The genetic code is ordered
o The genetic code contains start and stop codons
起始（ AUG）与终止（ UAA,UAG,UGA）
Synthesis of protein蛋白质的合成
? Initiation 启动
? Elongation 肽链延伸
? Termination 合成的终止
Mg2+
AA+ATP+E（酶） E.AA-AMP+ppi
E.AA-AMP+tRNA E+AA-RNA+AMP
Activation
活化
Initiation
启动
核糖体的结构
上图,30S
中图,50S
下图：核糖体
Elongation
肽 链 延 伸
The closing
Testing your knowledge
? What are the important properties of genetic
codes?
第四章 动物基因组：基因和 DNA
? Nucleic acids are genetic
materials核酸是遗传物质
? Structure of nucleic acids核
酸的结构
? Synthesis of nucleic acids核酸
的合成
? Gene structure基因结构
? Variations of gene and DNA
基因和 DNA的变异
? Translation,synthesis of
protein 蛋白质的合成 --翻译
Nucleic acids are genetic materials
核酸是遗传物质
Chromosome
染色体
protein蛋白质
DNA
RNA
Which one is genetic material?
哪一个 是遗传物质？
Experiments prove that DNA is
the molecule of heredity
? Transformation experiment with
pneumonia
? Transfection experiment with
bacteriophage
? Experiment with tabauo mosaic virus
(TMV)
Transformation experiment
肺炎球菌的转化实验
无毒的 RII肺炎
球菌（小的）由被杀
死的 SIII （大的）的
DNA转化成有毒的肺
炎球菌
Streptococus pneumoniae
肺炎球菌
? S型：多糖组成荚膜，分 SI,SII,SIII
? R型：无荚膜，分 RI,RII,RIII
Transformation
experiment with
pneumonia
肺炎球菌感染小
鼠实验
象加热杀死的 SIII能使不致
病的 RII变成能致病的 SIII,这种
现象叫转化 （ transformation）
把 SIII死菌中能转化 RII的物质叫
转化因子
证明转化因子
是 DNA的实验
A diagram of the experiment that
demonstrated that DNA is the active
material in bacterial transformation
Transfection experiment with bacteriophage T2
T2噬菌体的侵染实验 (I)
T2噬菌体的侵染实验 (II)
Experiment with tabauo mosaic virus (TMV)
烟草花叶病毒感染试验
Key points,The genetic information of living
organisms is stored in deoxyriboncleic acid
(DNA),In some viruses,ribonucleic acid
(RNA) is the genetic material
Nucleic acids
核酸
脱氧核糖核酸
(DNA)
核糖核酸
(RNA)
Structure of nucleic acids
核酸的结构
Size of genome基因组大小
Phylum Species Genome (bp)
Algae Pyrenomas salina 6.6× 105
Mycoplasma M.pneumoniae 1.0 × 106
Bacterium E.coli 4.2 × 106
Yeast S,cerevisiae 1.3 × 107
Slime mold D,discoideum 5.4 × 107
Nematode C,elegans 8.0 × 107
Insect D,Melanogaster 1.4 × 108
Bird G,domesticus 1.2 × 109
Amphibian X,laevis 3.1 × 109
Mammal H,sapiens 3.3 × 109
Nucleic acids are macromolecules composed
of repeating subunits called nucleotides,Each
nucleotide is composed of (1) a phosphate
group,(2) a five-carbon sugar (pentose),and (3)
a cyclic nitrogen-containing compound called a
base.
DNA的基本组成单位是 脱氧核苷酸。每个脱氧核苷
酸含有一个碱基，一个脱氧核糖和一个磷酸基。
碱
基
结
构
式
Chargaff法则
? 腺嘌呤与胸腺嘧啶的克分子数相等,A”=“T”
? 鸟嘌呤与胞嘧啶的克分子数相等,G”=“C”
The Watson-Crick double-helix
DNA双螺旋结构模型要点
? DNA usually exists as double helix,with the two
strands held together by hydrogen bonds
between the complementary bases,A paired
with T and G paired with C.
DNA分子是由两条同轴反向互相缠绕的多核甘酸链组成
的双螺旋结构
? 糖和磷酸排在外面构成骨架,两链相应的核甘酸的碱基
互相配对由氢键连接排列在内侧
? The base pairs in DNA are stacked about 0.34
nm apart,with 10 base pairs per turn (360゜ ) of
the double helix
双螺旋直径为 20A，螺距为 34A,包含 10对碱基
糖 -磷酸基团骨架
（黑色）以及碱基
（彩色）
DNA双螺旋横断面
RNA 的基本结构单位是核苷酸，它由
含氮碱基（ A,G,C,U），核糖和磷酸
基构成 。
Structure of RNA
含氮碱基（ A,G,C,U）和核酸
RNA的分类
? mRNA,冒子结构和尾巴
? tRNA：三叶草结构
? rRNA：大亚基和小亚基
Key points
? Nucleic acids are of two types,DNA and RNA
? DNA usually exists as double helix,with the two
strands held together by hydrogen bonds between
the complementary bases,A paired with T and G
paired with C
? The complementarity of the two strands of a double
helix makes DNA uniquely suited to store and
transmit genetic information from generation to
generation
? The two strands of a double helix have opposite
chemical polarity
? RNA usually exists as a single-stranded molecule
Testing your knowledge
? The E.coli virus ΦX174 stores its genetic information in
single-stranded DNA,When DNA was extracted from
ΦX174 virus particles and analyzed,21 percent of the
bases were found to be G residues,From this information,
can you determine what percentage of the bases in this
DNA were thymine residues? If so,what percentage? If
not,why not?
Synthesis of nucleic acids
核酸的合成
? DNA合成 复制 自体催化
? RNA合成 转录 异体催化
? Watson and Crick提出 半保留复制的设
想。如何论证？
Semi-conservative replication
DNA半保留复制 —CsCl2梯度离心
A.离心图带 B.扫描图
The diagram of CsCl2 density-
gradient centrifugation
CsCl2梯度离心示意图
Semi-conservative
replication
Synthesis
复制进行
The process of DNA synthesis
DNA复制过程
Initiation
复制起始
复制起始（ unwinding DNA双
螺旋解开 ）
? Helicases 解旋酶
? DNA-Binding Protein单链结合蛋白
（ SSB）
? Topoisomerases 拓朴异构酶
复制进行
在 RNA酶催化下，以 DNA为模板，
合成一小段 RNA作为引物，然后在
DNA聚合酶 III催化下，以脱氧核糖
核苷三磷酸（ dATP,dGTP,dTTP、
dCTP）为底物，以 DNA的两条单链
为模板合成与母链互补的子链。
Synthesis direction 合成方向
5’ 3’
Continuous synthesis of one strand;
Discontinuous synthesis of the other strand
(Okazaki fragment 冈崎片段 )
Leader strand前导链,3’ 5’
Lagging strand后随链,5’ 3’
Transcription 转录
这是以 DNA为模板，在依赖 DNA
的 RNA聚合酶作用下合成 RNA的过程。
RNA聚合酶的构成
α 亚基
β 亚基
β` 亚基
σ 亚基
核心酶
Nonsense chain,the chain is not transcripted
无意义链,没被转录的其中一条链
Sense chain,the chain is transcripted
有意义链,被转录的其中一条链
Key points
? DNA replication is complex,requiring the
participation of a large number of proteins
? DNA synthesis is continuous on the progeny
strand that is being extended in the overall 5’ 3’
direction,but discontinuous on the strand
growing in the overall 3’ 5’ direction
? New DNA chains are initiated by short RNA
primers synthesized by DNA primase
Gene structure基因结构
? Evolution of the concept of the gene,
summary
? Evolution of the concept of the gene,
function
? Evolution of the concept of the gene,
structure
? A genetic definition of the gene
? Complex gene-protein relationships
Evolution of the concept of the gene,summary
Gene structure
(a) Typical prokaryotic gene
(b)Typical eukaryotic gene
Gene structure
The concept of the gene has undergone many
refinements since its discovery by Mendel in 1866,
Most genes encode one polypeptide and can be
operationally defined by the complementation test.
Evolution of the concept of the gene,function
? Mendel,constant factors controlling phenotypic
traits
? Garrod,one mutant gene-one metabolic block
? Early evidence that enzymes are controlled by
genes
? Beadle and Tatum,One gene-one enzyme
? One gene-one polypeptide
Mendel,constant factors controlling
phenotypic traits
Garrod,one
mutant gene-one
metabolic block
Early evidence that
enzymes are
controlled by genes
Beadle and Tatum,
One gene-one enzyme
One gene-one polypeptide
The existence of a basic genetic element,
that controlled a specific phenotypic trait was
established by Mendel’s work in 1866,Since
the discovery of Mendel’s results in 1900,the
concept of the gene has evolved from unit that
can mutate to cause a specific block in meta-
bolism,to the unit specifying one enzyme,to
the sequence of nucleotide pairs in DNA encoding
one polypeptide chain.
Evolution of the concept of the gene,
structure
? The pre-1940 Beads-on-a-string concept
? Discovery of recombination within the
gene
? Recombination between adjacent
nucleotide pairs
? Colinearity between the coding sequence
of a gene and its polypeptide product
The concept of the gene has evolved
from a bead on a string,not divisible by
recombination or mutation,to a sequence
of nucleotide pairs in DNA encoding one
polypeptide chain,The unit of genetic
material not divisible by recombination or
mutation is the single nucleotide pair.
A genetic definition of the gene
? The complementation test as an
operational definition of the gene
? Intragenic complementation
? Limitations on the use of the
complementation test
The complementation test as an
operational definition of the gene
The arrangement of
genetic markers in
cis and trans hetero-
zygotes
The complementation test as an
operational definition of the gene
The cis-trans
position effect
The complementation test as an
operational definition of the gene
The cis test
The complementation test as an
operational definition of the gene
The trans test
Intragenic
complementation
Intragenic complementation
may occur when a protein is
a multimer containing at least
two copies of one gene product
Limitations on the use of the
complementation test
The complementation or trans test provides an
operational definition of the gene; it is used to
determine whether mutations are in the same gene
or different genes,Intragenic complementation
may occur when a protein is a multimer containing
at least two copies of one gene product.
Complex gene-protein relationships
? Alternate pathways of transcript
splicing,protein isoforms
? Assembly of genes during
development,human antibody
Alternate pathways of transcript
splicing,protein isoforms
Testing your knowledge
? The red alga Polyides rotundus stores its genetic
information in double-stranded DNA,When DNA
was extracted from P,rotundus cells and analyzed,
32 percent of the bases were found to be guanine
residues,From this information,can you determine
what percentage of the bases in the this DNA were
thymine residues? If so,what percentage? If not,
why not?
Variations of gene and DNA
基因和 DNA的变异
? Mutation and its basic features
基因突变及其特性
? The molecular basis of mutation
基因突变的分子基础
? DNA repair mechanisms
DNA损伤的修复
Mutation and its basic features
基因突变及其特性
? The term mutation refers to both (1) the change in the
genetic material and (2) the process by which the change
occurs,Today,the term mutation often is used in a
narrow sense to refer only to changes occurring within
genes 基因突变就是一个基因变为它的等位基因
? Mutation’s features基因突变的特性
? Mutation is a reversible process可逆性
? Multiple directions多方向性
? Low frequencies低频率性
The molecular basis of mutation
基因突变的分子基础
? Mutation types基因突变类型
? Effects of base substitution on
phenotypes 碱基置换突变的结果
? Mutation mechanism基因突变的机制
Mutation types基因突变类型
? Base substitution 碱基置换突变
? Transitions,嘌呤 嘌呤；嘧啶 嘧啶
? Transversions,嘌呤 嘧啶
? Frameshift mutations移码突变
? Deletion and addition of short fragments
片段突变
Effects of base substitution on
phenotypes 碱基置换突变的结果
? synonymous mutation同义突变
? non-synonymous mutation错义突变
? non-sense mutation无义突变
Mutation mechanism
基因突变的机制
? Mutations induced by chemicals
? 碱基类似物的诱发突变
? 改变 DNA化学结构的诱变剂
? 结合到 DNA上的诱变剂
? Mutations induced by radiation
? Mutations induced by transposable
genetic elements
The mutagenic base analogs
碱基类似物的诱发突变
5’-溴尿嘧啶
5-bromouracil
酮式：与 A配对
烯醇式：与 G配对
改变 DNA化学结构的诱变剂
A H,H-C亚硝酸
G mG,mG-T烷化剂
结合到 DNA上的诱变剂
? 吖 啶类化合物能结合到 DNA上，插入碱
基之间使它们分开，造成不等交换
? 吖 啶类化合物还能使 DNA分子插入一个
碱基或丢失一个碱基，产生移码突变
Mutations are induced by chemicals,ionizing
irradiation,ultraviolet light,and endogenous
transposable genetic elements that jump from one
position in the genome to new sites,Point mutations
are of three types,(1) transitions,purine for purine
and pyrimidine for pyrimidine substitutions,(2)
transversions,purine for pyrimidine and pyrimidine
for purine substitution,and (3) frameshift mutations,
additions or deletions of one or two nucleotide
pairs,which alter the reading frame of the gene
distal to the site of the mutation,Several inherited
human diseases are caused by expanded
trinucleotide repeats.
DNA损伤的修复（自学）
? 紫外线对 DNA的损伤
? 光复活作用
? 切除修复
? 重组修复
Translation:synthesis of protein
蛋白质的合成 ——翻译
DNA mRNA 蛋白质
核苷酸 氨基酸
核苷酸 氨基酸
Nucleotide Amino acid
Genetic code 遗传密码
Important properties of genetic codes
o The genetic code is composed of nucleotide
triplets三联体
o The genetic code is degenerate兼并性
o The genetic code is comma-free连续性
o The genetic code is nonoverlapping
o The genetic code is nearly universal通用性
o The genetic code is ordered
o The genetic code contains start and stop codons
起始（ AUG）与终止（ UAA,UAG,UGA）
Synthesis of protein蛋白质的合成
? Initiation 启动
? Elongation 肽链延伸
? Termination 合成的终止
Mg2+
AA+ATP+E（酶） E.AA-AMP+ppi
E.AA-AMP+tRNA E+AA-RNA+AMP
Activation
活化
Initiation
启动
核糖体的结构
上图,30S
中图,50S
下图：核糖体
Elongation
肽 链 延 伸
The closing
Testing your knowledge
? What are the important properties of genetic
codes?
