📚 The Mitotic Cell Cycle | 有丝分裂细胞周期
The mitotic cell cycle is the sequence of events by which a eukaryotic cell duplicates its genetic material and divides to produce two genetically identical daughter cells. Understanding this process is fundamental to growth, repair, and asexual reproduction in living organisms, and it is a core topic in the Cambridge A-Level Biology syllabus.
有丝分裂细胞周期是真核细胞复制其遗传物质并分裂产生两个基因相同子细胞的一系列事件。理解这一过程是生物体生长、修复和无性繁殖的基础，也是剑桥 A-Level 生物教学大纲的核心主题。
1. Chromosomes and DNA | 染色体与 DNA
In eukaryotic cells, DNA is packaged with histone proteins to form chromatin, which condenses into visible chromosomes during mitosis.
在真核细胞中，DNA 与组蛋白包装形成染色质，在有丝分裂期间凝缩成可见的染色体。
A replicated chromosome consists of two identical sister chromatids held together at a centromere. Each chromatid contains one identical DNA molecule.
复制后的染色体由两条相同的姐妹染色单体组成，它们在着丝粒处连接。每条染色单体含有一个相同的 DNA 分子。
The telomere is a protective cap at the end of each chromatid, preventing loss of genetic information during DNA replication.
端粒是每条染色单体末端的保护帽，可防止 DNA 复制过程中遗传信息的丢失。
The centromere is also the attachment point for spindle fibres during mitosis, allowing the chromatids to be pulled apart accurately.
着丝粒也是有丝分裂过程中纺锤丝的附着点，使染色单体能够被准确地拉开。
2. Diploid and Haploid Cells | 二倍体与单倍体细胞
A diploid cell (2n) contains two full sets of chromosomes, one set inherited from each parent. In humans, the diploid number is 46.
二倍体细胞（2n）含有两套完整染色体，分别来自每个亲本。人类的二倍体数为 46。
A haploid cell (n) contains only one set of chromosomes, such as gametes in animals. In humans, the haploid number is 23.
单倍体细胞（n）只含有一套染色体，例如动物的配子。人类的单倍体数为 23。
Mitosis maintains the diploid number, producing daughter cells that are genetically identical to the parent cell. This is different from meiosis, which produces haploid gametes.
有丝分裂维持二倍体数目，产生的子细胞与亲本细胞在基因上相同。这与减数分裂不同，减数分裂产生单倍体配子。
In multicellular organisms, most body cells are diploid, while only gametes are haploid. This distinction is essential for sexual reproduction and chromosome number stability across generations.
在多细胞生物中，大多数体细胞是二倍体，只有配子是单倍体。这种区别对于有性生殖和世代间染色体数目的稳定至关重要。
3. Overview of the Cell Cycle | 细胞周期概览
The cell cycle consists of interphase and the mitotic phase (M phase). Interphase is subdivided into G₁, S, and G₂ phases, while the M phase includes mitosis and cytokinesis.
细胞周期由间期和有丝分裂期（M 期）组成。间期细分为 G₁、S 和 G₂ 期，而 M 期包括有丝分裂和胞质分裂。
G₁ → S → G₂ → M (mitosis + cytokinesis)
Interphase is often incorrectly called the resting stage; it is actually a period of high metabolic activity, growth, and DNA replication.
间期常被错误地称为静止期；实际上它是代谢活跃、生长和 DNA 复制的时期。
The length of the cell cycle varies greatly between cell types. For example, mammalian skin cells divide frequently, while nerve cells may remain in a non-dividing state for the entire life of the organism.
不同细胞类型的细胞周期长度差异很大。例如，哺乳动物的皮肤细胞分裂频繁，而神经细胞可能在生物体整个生命期间都处于不分裂状态。
4. Interphase: G₁, S, G₂ | 间期：G₁、S、G₂ 期
During G₁ phase, the cell grows rapidly, synthesises proteins, and produces new organelles. The cell also carries out its normal specialised functions.
在 G₁ 期，细胞快速生长、合成蛋白质并产生新的细胞器。细胞还执行其正常的特化功能。
The G₁ checkpoint ensures that conditions are favourable for DNA replication. If the cell does not receive a go-ahead signal, it may enter a resting state called G₀.
G₁ 检查点确保条件有利于 DNA 复制。如果细胞未收到继续信号，它可能进入称为 G₀ 的静止状态。
During S phase, each DNA molecule is replicated semi-conservatively, producing two identical sister chromatids for each chromosome. This doubles the DNA content of the cell.
在 S 期，每条 DNA 分子通过半保留方式复制，使每条染色体产生两条相同的姐妹染色单体。这使细胞的 DNA 含量加倍。
During G₂ phase, the cell continues to grow, synthesises proteins needed for mitosis (such as tubulin for spindle fibres), and checks that DNA replication is complete and undamaged.
在 G₂ 期，细胞继续生长，合成有丝分裂所需的蛋白质（如纺锤丝的微管蛋白），并检查 DNA 复制是否完整且无损伤。
At the end of interphase, the cell contains replicated chromosomes, duplicated organelles, and sufficient energy stores to proceed through division.
在间期结束时，细胞含有已复制的染色体、复制的细胞器以及足够的能量储备，可以继续进行分裂。
5. Mitosis: Prophase and Metaphase | 有丝分裂：前期与中期
Mitosis is a continuous process divided into four stages for convenience: prophase, metaphase, anaphase, and telophase.
有丝分裂是一个连续过程，为方便起见分为四个阶段：前期、中期、后期和末期。
In prophase, chromatin condenses into visible chromosomes, each consisting of two sister chromatids. The nucleolus disappears and the nuclear envelope breaks down.
在前期，染色质凝缩成可见的染色体，每条染色体由两条姐妹染色单体组成。核仁消失，核膜解体。
Centrioles in animal cells migrate to opposite poles and begin to assemble the spindle fibres from microtubules. Plant cells lack centrioles but still form a spindle from microtubule organising centres.
动物细胞中的中心粒移向两极，并开始由微管组装纺锤丝。植物细胞没有中心粒，但仍由微管组织中心形成纺锤体。
In metaphase, the chromosomes align along the metaphase plate at the equator of the cell. Each chromosome is attached to spindle fibres from both poles at its centromere.
在中期，染色体排列在细胞赤道处的中期板上。每条染色体在着丝粒处与来自两极的纺锤丝连接。
The alignment at the metaphase plate ensures that when the chromatids separate, each new nucleus will receive one complete set of chromosomes.
染色体在中期板上的排列确保了当染色单体分离时，每个新细胞核都能获得一套完整的染色体。
6. Mitosis: Anaphase and Telophase | 有丝分裂：后期与末期
At the start of anaphase, the centromeres divide, and the spindle fibres shorten, pulling the sister chromatids apart to opposite poles. Once separated, each chromatid is called a chromosome.
在后期开始时，着丝粒分裂，纺锤丝缩短，将姐妹染色单体拉向相反两极。一旦分开，每条染色单体就被称为染色体。
The cell becomes temporarily elongated as the poles move further apart. This ensures each pole receives an identical set of chromosomes.
随着两极进一步分开，细胞暂时被拉长。这确保每一极获得一套相同的染色体。
In telophase, the chromosomes decondense back into chromatin. New nuclear envelopes form around each set of chromosomes, and the nucleoli reappear.
在末期，染色体解凝缩回染色质。每组染色体周围形成新的核膜，核仁重新出现。
The spindle fibres break down, and two genetically identical nuclei are now present in one cell. Each nucleus contains the same diploid chromosome number as the original parent cell.
纺锤丝解体，此时一个细胞内存在两个基因相同的细胞核。每个细胞核含有与原始亲本细胞相同的二倍体染色体数。
7. Cytokinesis in Animal and Plant Cells | 动物和植物细胞的胞质分裂
Cytokinesis is the division of the cytoplasm, which usually begins during late anaphase or telophase and completes after mitosis.
胞质分裂是细胞质的分裂，通常在后期晚期或末期开始，并在有丝分裂后完成。
In animal cells, a cleavage furrow forms as a ring of actin and myosin microfilaments contracts around the equator, pinching the cell into two daughter cells.
在动物细胞中，随着肌动蛋白和肌球蛋白微丝环在赤道周围收缩，形成分裂沟，将细胞夹成两个子细胞。
In plant cells, because of the rigid cell wall, a cell plate forms at the equator. Vesicles from the Golgi apparatus fuse to build a new cell wall and cell membrane across the middle of the cell.
在植物细胞中，由于存在坚硬的细胞壁，因此赤道处形成细胞板。来自高尔基体的囊泡融合，在细胞中部构建新的细胞壁和细胞膜。
In both cases, cytoplasmic organelles are shared between the two daughter cells, though not always exactly equally.
在这两种情况下，细胞质细胞器在两个子细胞之间分配，但并不总是完全均等。
8. Significance of Mitosis | 有丝分裂的意义
Mitosis produces two daughter cells that are genetically identical to the parent cell and to each other, because the DNA is replicated exactly during S phase and separated precisely during anaphase.
有丝分裂产生两个与亲本细胞及彼此基因相同的子细胞，因为 DNA 在 S 期被精确复制，并在后期被精确分离。
It is essential for growth of multicellular organisms, replacement of damaged or worn-out cells, and repair of tissues after injury.
它对多细胞生物的生长、受损或衰老细胞的替换以及损伤后组织的修复至关重要。
In some organisms, mitosis is also used for asexual reproduction, producing clones of the parent. Examples include budding in yeast, vegetative propagation in plants, and binary fission in some single-celled eukaryotes.
在某些生物体中，有丝分裂也用于无性繁殖，产生亲本的克隆。例如酵母的出芽生殖、植物的营养繁殖以及一些单细胞真核生物的二分裂。
Mitosis also ensures genetic stability, because each daughter cell receives the same number and type of chromosomes as the parent cell. This is crucial for maintaining normal cell function within a tissue.
有丝分裂还确保遗传稳定性，因为每个子细胞都获得与亲本细胞相同数量和类型的染色体。这对于维持组织内正常细胞功能至关重要。
9. Control of the Cell Cycle and Cancer | 细胞周期的调控与癌症
The cell cycle is tightly controlled by internal and external signals at checkpoints, especially in G₁, G₂, and during metaphase at the spindle assembly checkpoint.
细胞周期在检查点受到内外信号的严格控制，尤其是在 G₁ 期、G₂ 期和中期纺锤体组装检查点处。
Cyclin proteins and cyclin-dependent kinases (CDKs) regulate progression through the cell cycle. Their concentrations rise and fall in a coordinated manner, triggering the cell to move from one phase to the next.
细胞周期蛋白和细胞周期蛋白依赖性激酶（CDK）调控细胞周期的进程。它们的浓度以协调的方式升降，触发细胞从一个阶段进入下一个阶段。
Cancer is a disease of uncontrolled cell division, often caused by mutations in genes that code for checkpoint proteins, such as p53. These mutations allow cells to bypass normal controls and divide repeatedly, forming a tumour.
癌症是一种细胞分裂失控的疾病，通常由编码检查点蛋白（如 p53）的基因突变引起。这些突变使细胞绕过正常控制，反复分裂，形成肿瘤。
If cells from a tumour spread to other parts of the body and form secondary tumours, the cancer is said to have metastasised. Malignant tumours can invade nearby tissues and disrupt normal organ function.
如果肿瘤细胞扩散到身体其他部位并形成继发性肿瘤，则癌症已发生转移。恶性肿瘤可侵入附近组织并破坏正常器官功能。
10. Observing Mitosis: Root Tip Squash | 观察有丝分裂：根尖压片
The root tip of a plant is a common specimen for observing mitosis because it contains a meristem, a region of rapidly dividing cells.
植物根尖是观察有丝分裂的常用标本，因为它含有分生组织，即快速分裂的细胞区域。
A typical procedure involves staining the root tip with a dye such as toluidine blue or Feulgen stain, macerating it with acid, and squashing it under a coverslip to spread the cells into a single layer.
典型步骤包括用甲苯胺蓝或孚尔根染液等染料对根尖染色，用酸浸软，并在盖玻片下压片，使细胞分散成单层。
The cells are then viewed under a light microscope, and cells in prophase, metaphase, anaphase, and telophase can be identified by their chromosome arrangement.
然后在光学显微镜下观察细胞，根据染色体排列可识别出处于前期、中期、后期和末期的细胞。
The mitotic index can be calculated as the number of cells undergoing mitosis divided by the total number of cells visible; it gives an estimate of the rate of cell division.
有丝分裂指数可计算为正在进行有丝分裂的细胞数除以可见细胞总数；它可估算细胞分裂的速率。
mitotic index = (number of cells in mitosis ÷ total number of cells) × 100%
When preparing the root tip squash, it is important to use the very tip of the root, about 1-2 mm, because this is where the meristem cells are actively dividing. Staining makes the chromosomes visible so the stages can be distinguished.
在制备根尖压片时，重要的是使用根尖最末端约 1-2 mm 的部分，因为这是分生组织细胞活跃分裂的部位。染色使染色体可见，从而可以区分不同阶段。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply