一、Term
Chromosomes染色体
Chromatin染色质
Nucleoid拟核
Capsid衣壳
nucleation center成核中心
terminase末端酶（DNA病毒装配）
Nucleoid-associated proteins拟核相关蛋白（大概占nucleoid的20%质量）
Bacterial condensin complexes细菌凝聚素复合体
Torsional tension扭转张力
Supercoiling超螺旋
matrix attachment regions (MARs)基质附着序列
Euchromatin常染色质
Heterochromatin异染色质
constitutive heterochromatin组成型异染色质
centromere着丝粒（是DNA）：重复序列以及H3变体
kinetochore着丝点；动粒（是蛋白质）
telomere端粒
meiotic减数分裂
Telomerase端粒酶
Nucleosome核小体
Histone组蛋白
Histone tails组蛋白尾巴
10nm fiber 10nm纤维
Linker histones连接组蛋白（如H1，与核心组蛋白相区分）
Nonhistone非组蛋白（染色体的其他结构蛋白）
MNase(micro coccal nuclease)微球核酸酶（能切出单独的核小体）
Histone octamer组蛋白八聚体
core DNA核心DNA（约146bp，核小体就200bp左右）
Linker DNA连接DNA
histone code组蛋白密码
chromosome scaffold染色体骨架
indirect end labeling间接末端序列
nucleosome positioning核小体定位
二、判断
Chromosomes is visible as a morphological entity only during cell division.染色体只有在细胞分裂时才能看到形态实体。
chromatin–The state of nuclear DNA and its associated proteins during the interphase (between mitoses) of the eukaryotic cell cycle. 染色质是真核细胞周期间期(有丝分裂间期)核DNA及其相关蛋白的状态
Nucleoid拟核The structure in a prokaryotic cell that contains the genome.
matrix attachment regions (MARs)基质附着序列：DNA is attached to the nuclear matrix at specific sequences
The MARs are A-T-rich but do not have any specific consensus sequence.
We can see individual chromosomes only during mitosis.有丝分裂
着丝粒特点Centromeres in higher eukaryotic chromosomes contain large amounts of repetitive DNA 重复DNA and unique histone H3 variants.独特的H3变体
端粒酶在Telomerase uses the 3′–OH of the G+T telomeric strand and its own RNA template用自身的RNA模版 to iteratively add tandem repeats串联重复序列 (5′-TTAGGG-3′ in human) to the 3′ end at each chromosomal terminus.在染色体3‘末端
nucleosome 核小体：The basic structural subunit of chromatin是染色质的基本结构, consisting of about 200 bp of DNA and an octamer of histone proteins.
Histone tails组蛋白尾巴–Flexible amino- or carboxy-terminal regions of the core histones that extend beyond the surface of the nucleosome.
Histone tails are sites of extensive posttranslational modification.组蛋白尾巴是广泛的翻译后修饰位点。
Linker histones bind nucleosomes and/or linker DNA and promote 30 nm fiber formation. 连接组蛋白结合核小体或连接DNA，并促进30 nm纤维的形成。
30nm fiber–A coil of nucleosomes.– It is the basic level of organization of nucleosomes in chromatin. 30nm纤维是染色质中核小体组织的基本水平。
The length of DNA per nucleosome variesfor individual tissues or species in a range from 154 to 260 bp.核小体DNA的长度大概在154-260bp
Nucleosomal DNA is divided into the core DNA and linker DNA depending on its susceptibility to MNase. 根据核小体DNA对MNase的敏感性，可将其分为核心DNA和连接DNA。
A nucleosome contains approximately 200bp of DNA and two copies of each core histone (H2A, H2B, H3, and H4).核心八聚体
DNA is wrapped around the outside surface of the protein octamer. DNA被包裹在蛋白质八聚体的外表面。
30-nm fibers are a prevalent type of secondary structure 30nm粗丝是普遍的二级结构。
Most transcribed genes retain a nucleosomal structure, though the organization of the chromatin changes during transcription.大多数转录的基因保留了核小体的结构
- Someheavilytranscribedgenesappeartobe exceptional cases that are devoid of nucleosomes.
- RNA polymerase displaces histone octamers during transcription in vitro, but octamers reassociate with DNA as soon as the polymerase has passed.
三、简答
1、constitutive heterochromatin组成型异染色质特点
- It is permanently or nearly always condensed.浓缩
- It replicates late in S phase在S期后期进行复制
- It has a reduced frequency of genetic recombination relative to euchromatic gene-rich areas of the genome.重组频率很低（遗传距离也不准）
- It often consists of multiple repeats of a few sequences of DNA通常由几个DNA序列的多个重复组成。
- The DNA in this region are not transcribed or are transcribed at very low levels. 没有转录，或者转录水平很低。
- The density of genes in this region is very much reduced compared with euchromatin.
2、The functions of telomere端粒的功能
- The first is to protect the chromosome end and maintain its stability. 保护染色体末端、维持染色体的稳定性—for example, the end generated by a double-strand break—becomes a target for repair systems. The cell must be able to distinguish the telomere and any other end.细胞要将双链末端断裂与端粒区分开
- The second is to allow the telomere to be extended.保证端粒能够延伸 If it is not extended, it becomes shorter with each replication cycle (because replication cannot initiate at the very end).
- The third is to facilitate meiotic chromosome reorganization for efficient pairing and recombination of homologouschromosomes. 促进了染色体的重组，实现了同源染色体的高效配对和重组
3、染色体的三个基本条件：
The minimum features required for existence as a chromosome are as follows:
- Telomeres to ensure survival端粒
- A centromere to support segregation着丝粒
- An origin to initiate replication复制起始
4、组蛋白
5、染色质中DNA与蛋白质紧密结合的实验证据：
6、How does the higher-order chromatin and chromosome structure form?染色体和染色质形成？
(1) The nucleosome Filament染色质的10nm纤维细丝
Histone H1 binds to the linker DNA between nucleosome, inducing tighter DNA wrapping around the nucleosome
(2) The 30-nm Fiber染色质的30nm螺线管粗丝结构——染色质日常状态
Nucleosome arrays can form more complex structures: the 30-nm fiber (“zigzag model”)
(3) 靠染色体骨架进行压缩。形成有丝分裂的三维结构等
Histone octamers are not conserved during replication, but H2A-H2B dimers and H32-H42 tetramers are.
There are different pathways for the assembly of nucleosomes during replication and also independent of replication.
7、核小体能够在特定位置形成？
原因是local structure of DNA（DNA本身的结构） or proteins that interact with specific sequences.（与特定序列互作的蛋白）
使用的技术是indirect end labeling间接末端标记
–A technique for examining the organization of DNA by making a cut at a specific site and identifying all fragments containing the sequence adjacent to one side of the cut.
然后使用MNase微球核酸酶处理，得到200bp的核小体缠绕单元，然后再用限制性内切酶，切某个特定位点，末端用探针。
实验结果显示一个条带，说明核小体总是能够在特定位置形成。
Suppose that the DNA sequence is organized into nucleosomes in only one particular configuration so that each site on the DNA always is located at a particular position on the nucleosome. This type of organization is called nucleosome positioning核小体定位