Chapter 1 DNA and Chromosome
1.2.2 DNA的一级结构是指4种核苷酸的连接及其排列顺序，表示了该DNA分子的化学组成。(1)DNA分子是由4种脱氧核苷酸组成的两条互相平行的脱氧核苷酸长链盘绕而成，方向相反，一条5´3´，另一条3´5´。(2)DNA分子中的脱氧核糖和磷酸交替连接，排在外侧，构成基本骨架，碱基排列在内侧。(3)两条链上的碱基通过氢键相结合，形成碱基对。它的组成有一定的规律，腺嘌呤（A）只能与胸腺嘧啶（T）配对，鸟嘌呤（G）只能与胞嘧啶（C）配对。碱基之间的这种一一对应关系叫碱基互补配对原则。26个英文字母写法
DNA的二级结构是指两条多核苷酸链反向平行盘绕所生成的双螺旋结构。主要分两类：右手螺旋，如A-DNA，B-DNA，C-DNA。左手螺旋，Z-DNA。也发现有三链甚至四链DNA螺旋。Watson and Crick 提出的双螺旋模型: B-DNA是由两条反向平行的多核苷酸链围绕同一中心轴构成的右手螺旋结构，一条5´3´，另一条3´5´。链间有螺旋型的凹槽，其中一条较浅而窄，叫小沟，一条较深而宽，叫大沟。大沟在DNA与蛋白质相互作用、遗传信息识别方面非常重要。配对碱基平面与螺旋纵轴垂直，螺旋的轴心穿过氢键的中点。相邻碱基对平面之间的距离为0.34nm，顺中心轴方向，每隔0.34nm有一个核苷酸，3.4nm为一个结构重复周期（螺距)，含10个碱基对。双螺旋的直径2.0nm。
1.3.3 A chromosome is a discrete unit of the genome carrying many genes. Each chromosome consists of a very long molecule of duplex DNA and an approximately equal mass of proteins. It is visible as a morphological entity only during cell division.
1.4.1 A gene is a stretch of DNA that functions as a unit to give ri to an RNA or protein product; it may include exons and introns.
An exon is any gment of a gene that is reprented in the mature RNA product.
An intron is any gment of a gene that is transcribed, but removed from the transcript in RNA splicing.
1.4.3
Single nucleotide polymorphism (SNP) describes a polymorphism (variation in quence between individuals) caud by a change in a single nucleotide. This is responsible for most of the genetic variation between individuals.
Restriction fragment length polymorphism (RFLP) refers to inherited differences in sites for restriction enzymes (for example, caud by ba changes in the target site) that result in differences in the lengths of the fragments produced by cleavage with the relevant restriction enzyme.
Summary龙文一对一收费标准
The eukaryotic cell contains a membranous nucleus that includes the chromosome as carriers of genetic information.
The chromosomal DNA of eukaryotes is packaged into a highly regular nucleoprotein complex called chromatin.
A typical eukaryotic gene is monocistronic (单顺反子）.
Many DNA gments contain highly repeated quences.
Eukaryotic genes are split with the noncoding introns.
具有细胞核，遗传物质以染色质（体）形式存在，还存在有亚细胞区室（如线粒体、叶绿体）。
Chapter 2 DNA Replication
2.1 The parental duplex is replicated to form two daughter duplexes, each of which consists of one parental strand and one (newly synthesized) daughter strand. This behavior is called miconrvative replication.
2.3.1 地点英语D环复制：一种特殊的单向复制，不对称复制方式。线粒体和叶绿体的环状DNA以D环形式复制。线粒体DNA的复制：以双链环状DNA中一条亲代链（H链）为模板， 从H链的复制起点开始合成与之互补的新生L链，取代亲代L链，形成形状如D的取代环（ D-loop）。新生L链达到2/3处时，露出亲代L链上的复制起点，开始新生H链的合成。H链的复制起点与L链不在一个起点，形成不对称复制。
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2.3.2 滚环状复制 (rolling circle)是一种单向复制的特殊方式。许多病毒、细菌因子以及特定基因（rDNA in the Xenopus oocyte）放大的复制方式。在双链环状DNA（+）链的复制
起始点位置上进行单链特异性切断，游离出一个3´-OH和5´-磷酸基末端。在DNA聚合酶的作用下，以环状（-）链为模板，从正链的3´-OH端加入脱氧核苷酸，使链不断延长，通过滚动而合成出新的正链。可以合成比原有DNA长好几倍的单链。 5´端不断延长的游离尾巴很快被单链DNA结合蛋白结合，到一定长度后，5´端单链被切割成正链单体，进而复制最终形成双链环状DNA； 5´端单链也可以复制其互补链，经切割最终形成双链环状DNA 。
滚环状复制又叫复制。
2.3.3 复制:是一种双向复制的方式，是许多细菌基因组的复制方式。以E. coli基因组为例：复制启始时，在复制起点（oriC）DNA双链解旋，形成两个方向相反的复制叉。复制叉分别向两个方向延伸，在复制终点相遇完成复制过程。
2.4.1 DNA聚合酶 I
1) 5’3’聚合活性：要求有DNA双链模板和具有3’-OH的引物，在引物3’-OH端逐个加上dNTP，新链的生长方向总是5'3'。
2) 3’5’外切活性：识别不配对碱基,停止聚合活性，激活3’5’外切活性，切除不配对碱基。
3) 5’3’外切活性：即从5´-P端逐个切除核苷酸的活性。必须有5´-P末端；被切除的核苷酸必须是氢键配对的；被切除的核苷酸可以是脱氧核糖核苷酸，也可以是核糖核苷酸，这一活性的主要功能是缺口平移切修复突变和去除复制过程中后随链的引物。
Klenow酶：DNA聚合酶I是单一肽链的蛋白质（103 kD)，用枯草杆菌蛋白酶水解得到一个N端的小片段和C端的大片段。68kD大片段被称为Klenow片段，具有5'3'聚合活性和3'5'外切活性。
2.4.2
DnaA: binds to 9 bp repeat quences at oriC, then acts at three A-T-rich 13 bp tandem repeats, and melts the DNA strands to form an open complex in the prence of ATP.ancestors
DnaB预科是什么: extends the unwinding region with its helica activity, and activates DnaG prima.preventfrom
DnaC: binds to DnaB to form DnaB·DnaC complex, and then transfers DnaB to OriC. DnaC hydrolyzes ATP in order to relea DnaB.
性别 英语HU: a general DNA-binding protein in E. coli. Its prence is not absolutely required to initiate replication in vitro, but it stimulates the reaction.
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2.4.3
Semidiscontinuous replication is a DNA replication mode in which one new strand (the leading strand) is synthesized continuously while the other (the lagging strand) is synthesized discontinuously in the form of short fragments (5’ –3’ ) that are later connected into a covalently intact strand.
Okazaki fragments are the short stretches (1000-2000 bas) of the lagging strand produced during discontinuous DNA replication; they are later joined into a covalently intact strand.
