双螺旋 发现DNA结构的故事怎么样

C

对于常见的B-DNA
10个碱基绕一圈
碱基之间螺距为0.34nm
所以螺旋一圈距离是3.4nm
至于一个DNA分子到底有多长就由它有多少碱基对和包装的紧密程度来决定
希望能帮到你哟~

维系两条链的是链间氢键,而且A和T间是两条氢键,G和C间是三条氢键.
每条链内的脱氧核糖核苷酸之间则是靠3',5'-磷酸二酯键（属于共价键）连接的.
氢键较弱,所以DNA容易热变性.

超螺旋和左旋 右旋 没有必然联系
负超螺旋 就是把原来的螺旋放松
正超螺旋 就是把原来的螺旋拧紧
右手螺旋的可以有负超螺旋（松）和正超螺旋（紧）
左手螺旋可以有负超螺旋（松）和正超螺旋（紧）

是不是因为核糖和脱氧核糖的区别造成的.核糖的2位碳原子上是羟基,而脱氧核糖的2位碳原子上是H,核糖多了一个氧,氧要占有一定空间,所以,RNA难以形成象DNA一们的双螺旋结构.但某些病毒中也存在双链RNA的情况.

双螺旋只是在正常情况下维持DNA结构稳定用的.而DNA要发挥生物学功能,如遗传、表达等,都需要打开双螺旋结构才能进行.

解题思路：DNA分子是由2条反向平行的脱氧核糖核苷酸链组成的规则的双螺旋结构，脱氧核糖和磷酸交替连接，排列在外侧构成基本骨架，碱基排列在内侧，两条链上的碱基通过氢键连接形成碱基对，碱基对之间遵循A与T配对，G与C配对的碱基互补配对原则．

A、DNA分子是由2条反向、平行的脱氧核糖核苷酸链组成，A正确；
B、DNA分子的2条链上的碱基通过氢键连接，形成碱基对，B正确；
C、DNA分子中的碱基互补配对原则是A与T配对，G与C配对，C正确；
D、DNA分子的脱氧核糖和磷酸交替连接，排列在外侧构成基本骨架，D错误．
故选：D．

点评：
本题考点： DNA分子结构的主要特点．

考点点评： 对于DNA分子结构特点的理解和识记是本题考查的重点．

由图可知：①是染色体，②是DNA．细胞核内有染色体，染色体是指细胞核容易被碱性染料染成深色的物质，它是由DNA和蛋白质两种物质组成，DNA为双螺旋状结构．DNA是主要的遗传物质．一条染色体上包含一个DNA分子．一个DNA分子上包含有多个基因，基因是DNA上具有特定遗传效应的片段．DNA上有遗传信息，这些遗传物质的片段就是一个个的基因，基因决定生物的性状．
故选D

A、转录过程以DNA的一条链为模板，以核糖核苷酸为原料形成RNA的过程，因此需要解旋酶解旋打开双螺旋结构并需要RNA聚合酶催化，A正确；
B、转录时是先以DNA单链为模板形成RNA-DNA杂交区域，然后RNA与DNA分离，形成的产物是RNA单链，B正确；
C、翻译时，一个mRNA可以结合多个核糖体，但是一个核糖体上不能结合多个mRNA，C错误；
D、翻译过程中核糖体读取mRNA上决定氨基酸种类的密码子，D正确．
故选：C．

解旋酶 与 解链酶 是一种酶
在复制和转录的过程中
将DNA双螺旋解旋,线性化
使得DNA内部的信息可以被识别

解题思路：阅读题干可知，该题的知识点是双链DNA分子的结构特点，回忆DNA分子的结构特点，然后分析选项进行解答．

A、DNA分子是由两条链组成的，这两条链是反向、平行的，A正确；
B、DNA分子的脱氧核糖和磷酸交替连接，排列在外侧构成基本骨架，B正确；
C、由C分析可知，C错误；
D、两条链上的碱基，通过氢键连接形成碱基对，D正确．
故选：C．

点评：
本题考点： DNA分子结构的主要特点．

考点点评： 对于DNA分子双螺旋结构模型的理解、掌握是解题的关键．

直径咯～～～

解题思路：DNA分子结构的主要特点：DNA是由两条反向平行的脱氧核苷酸长链盘旋而成的双螺旋结构；DNA的外侧由脱氧核糖和磷酸交替连接构成的基本骨架，内侧是碱基通过氢键连接形成的碱基对，碱基之间的配对遵循碱基互补配对原则（A-T、C-G）．

DNA分子是由两条脱氧核苷酸长链盘旋成规则的双螺旋结构，DNA分子中脱氧核糖和磷酸交替交替排列的顺序稳定不变．DNA分子双螺旋结构中间为碱基对，碱基之间形成氢键，从而维持了双螺旋结构的稳定；DNA分子两条链间对应碱基严格按照碱基互补配对原则进行配对．
故答案为：
双螺旋 磷酸 脱氧核糖 氢 碱基互补配对

点评：
本题考点： DNA分子结构的主要特点；碱基互补配对原则；DNA分子的多样性和特异性．

考点点评： 本题考查DNA分子结构，要求学生识记DNA结构的内容．

A
B
D
C存在左手螺旋
E右手螺旋为3.6,左手更紧些

你好,
电镜下可以看到DNA是团被深染的结构,不能清晰的辨明结构,难以观察到双螺旋结构.
当初发现双螺旋结构的时候是通过物理学X射线衍射和理论模型共同的得出的结论,想直接观察到比较困难.
希望对你帮助：）

DNA Deoxyribonucleic acid ( /diksrabonuklek sd/ ) ( DNA ) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints or a recipe, or a code, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription. Within cells, DNA is organized into long structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. [1] In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. Properties DNA is a long polymer made from repeating units called nucleotides. [2] [3] [4] The DNA chain is 22 to 26 ngstrms wide (2.2 to 2.6 nanometres), and one nucleotide unit is 3.3 (0.33 nm) long. [5] Although each individual repeating unit is very small, DNA polymers can be very large molecules containing millions of nucleotides. For instance, the largest human chromosome, chromosome number 1, is approximately 220 million base pairs long. [6] In living organisms, DNA does not usually exist as a single molecule, but instead as a pair of molecules that are held tightly together. [7] [8] These two long strands entwine like vines, in the shape of a double helix. The nucleotide repeats contain both the segment of the backbone of the molecule, which holds the chain together, and a base, which interacts with the other DNA strand in the helix. A base linked to a sugar is called a nucleoside and a base linked to a sugar and one or more phosphate groups is called a nucleotide. If multiple nucleotides are linked together, as in DNA, this polymer is called a polynucleotide. [9] The backbone of the DNA strand is made from alternating phosphate and sugar residues. [10] The sugar in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings. These asymmetric bonds mean a strand of DNA has a direction. In a double helix the direction of the nucleotides in one strand is opposite to their direction in the other strand: the strands are antiparallel. The asymmetric ends of DNA strands are called the 5′ (five prime) and 3′ (three prime) ends, with the 5' end having a terminal phosphate group and the 3' end a terminal hydroxyl group. One major difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA being replaced by the alternative pentose sugar ribose in RNA. [8] The DNA double helix is stabilized by hydrogen bonds between the bases attached to the two strands. The four bases found in DNA are adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). These four bases are attached to the sugar/phosphate to form the complete nucleotide, as shown for adenosine monophosphate. These bases are classified into two types; adenine and guanine are fused five- and six-membered heterocyclic compounds called purines, while cytosine and thymine are six-membered rings called pyrimidines. [8] A fifth pyrimidine base, called uracil (U), usually takes the place of thymine in RNA and differs from thymine by lacking a methyl group on its ring. Uracil is not usually found in DNA, occurring only as a breakdown product of cytosine. In addition to RNA and DNA, a large number of artificial nucleic acid analogues have also been created to study the proprieties of nucleic acids, or for use in biotechnology. [12] Grooves Twin helical strands form the DNA backbone. Another double helix may be found by tracing the spaces, or grooves, between the strands. These voids are adjacent to the base pairs and may provide a binding site. As the strands are not directly opposite each other, the grooves are unequally sized. One groove, the major groove, is 22 wide and the other, the minor groove, is 12 wide. [13] The narrowness of the minor groove means that the edges of the bases are more accessible in the major groove. As a result, proteins like transcription factors that can bind to specific sequences in double-stranded DNA usually make contacts to the sides of the bases exposed in the major groove. [14] This situation varies in unusual conformations of DNA within the cell (see below), but the major and minor grooves are always named to reflect the differences in size that would be seen if the DNA is twisted back into the ordinary B form. Base pairing Each type of base on one strand forms a bond with just one type of base on the other strand. This is called complementary base pairing. Here, purines form hydrogen bonds to pyrimidines, with A bonding only to T, and C bonding only to G. This arrangement of two nucleotides binding together across the double helix is called a base pair. As hydrogen bonds are not covalent, they can be broken and rejoined relatively easily. The two strands of DNA in a double helix can therefore be pulled apart like a zipper, either by a mechanical force or high temperature. [15] As a result of this complementarity, all the information in the double-stranded sequence of a DNA helix is duplicated on each strand, which is vital in DNA replication. Indeed, this reversible and specific interaction between complementary base pairs is critical for all the functions of DNA in living organisms. [3] The two types of base pairs form different numbers of hydrogen bonds, AT forming two hydrogen bonds, and GC forming three hydrogen bonds (see figures, left). DNA with high GC-content is more stable than DNA with low GC-content, but contrary to popular belief, this is not due to the extra hydrogen bond of a GC base pair but rather the contribution of stacking interactions (hydrogen bonding merely provides specificity of the pairing, not stability). [16] As a result, it is both the percentage of GC base pairs and the overall length of a DNA double helix that determine the strength of the association between the two strands of DNA. Long DNA helices with a high GC content have stronger-interacting strands, while short helices with high AT content have weaker-interacting strands. [17] In biology, parts of the DNA double helix that need to separate easily, such as the TATAAT Pribnow box in some promoters, tend to have a high AT content, making the strands easier to pull apart. [18] In the laboratory, the strength of this interaction can be measured by finding the temperature required to break the hydrogen bonds, their melting temperature (also called T m value). When all the base pairs in a DNA double helix melt, the strands separate and exist in solution as two entirely independent molecules. These single-stranded DNA molecules have no single common shape, but some conformations are more stable than others. [19]
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