Telomeres: Their Biological Significance | 端粒的生物学意义

📚 Telomeres: Their Biological Significance | 端粒的生物学意义

Telomeres are specialised DNA-protein structures located at the ends of eukaryotic chromosomes. They play a fundamental role in protecting genetic information, regulating cell division, and influencing the processes of ageing and cancer. This article explores the structure, function, and broader biological implications of telomeres, tailored to the CIE A-Level Biology syllabus.

端粒是真核生物染色体末端特化的 DNA-蛋白质结构。它们在保护遗传信息、调控细胞分裂以及影响衰老和癌症进程中发挥着根本性的作用。本文围绕 CIE A-Level 生物学考纲，深入探讨端粒的结构、功能及其更广泛的生物学意义。

1. What Are Telomeres? | 什么是端粒？

Telomeres are repetitive nucleotide sequences located at the tips of linear chromosomes. In humans, the repeating unit is TTAGGG, which is typically repeated thousands of times, extending for 5–15 kilobases in somatic cells.

端粒是位于线性染色体末端的重复核苷酸序列。在人类中，重复单元为 TTAGGG，通常重复数千次，在体细胞中延伸长度为 5–15 千碱基。

These sequences are not random; their specific pattern is highly conserved across vertebrates, reflecting their essential function. Telomeric DNA is associated with a six-protein complex called shelterin, which protects the chromosome ends from being recognised as double-strand breaks by the DNA damage response machinery.

这些序列并非随机排列；其特定模式在脊椎动物中高度保守，反映了它们的重要功能。端粒 DNA 与一种称为 shelterin 的六蛋白复合物结合，保护染色体末端不被 DNA 损伤应答机制识别为双链断裂。

Without telomeres, the natural ends of chromosomes would be mistaken for damaged DNA, triggering inappropriate repair events such as end-to-end fusion or degradation.

如果没有端粒，染色体的天然末端就会被误认为是受损的 DNA，从而触发错误的修复事件，如末端融合或降解。

2. The Protective Role of Telomeres | 端粒的保护作用

Telomeres serve as protective caps that distinguish chromosome ends from broken DNA. This distinction is critical because the DNA damage response normally initiates cell cycle arrest and DNA repair when double-strand breaks are detected.

端粒作为保护性“帽子”，将染色体末端与断裂的 DNA 区分开来。这种区分至关重要，因为 DNA 损伤应答通常会在检测到双链断裂时启动细胞周期阻滞和 DNA 修复。

Specifically, the single-stranded G-rich overhang at the 3′ end of telomeric DNA can form a T-loop structure, where the overhang invades the double-stranded region of the telomere. This sequesters the free end and prevents it from activating ATM (ataxia-telangiectasia mutated) or ATR (ATM and Rad3-related) kinase pathways.

具体而言，端粒 DNA 3′ 端的富含鸟嘌呤的单链突出可以形成 T 环结构，即该突出部分侵入端粒的双链区域。这隔离了游离末端，阻止其激活 ATM（共济失调毛细血管扩张突变）或 ATR（ATM 与 Rad3 相关）激酶通路。

Additionally, telomeres prevent the loss of genetic information during DNA replication. The outermost regions of chromosomes contain essential genes; without a disposable buffer sequence, each round of replication would erode into coding DNA, leading to progressive loss of vital genetic material.

此外，端粒防止 DNA 复制过程中遗传信息的丢失。染色体的最末端区域含有必需基因；如果没有可消耗的缓冲序列，每一轮复制都会侵蚀到编码 DNA 中，导致关键遗传物质的逐步丢失。

The protective function also extends to preventing chromosome fusion. In the absence of telomeres, chromosome ends can be joined together by non-homologous end joining, creating dicentric chromosomes that break unpredictably during mitosis.

保护功能还延伸至防止染色体融合。在没有端粒的情况下，染色体末端可以通过非同源末端连接连接在一起，产生双着丝粒染色体，这些染色体在有丝分裂期间会不可预测地断裂。

3. The End-Replication Problem | 末端复制问题

DNA polymerase is unidirectional; it synthesises new DNA only in the 5′ to 3′ direction. This creates a fundamental challenge for replicating the ends of linear chromosomes.

DNA 聚合酶是单方向的；它只能沿 5′→3′ 方向合成新 DNA。这为线性染色体末端的复制带来了根本性的挑战。

On the leading strand, the first primer is placed at the very 3′ end of the template, allowing continuous synthesis to the chromosome terminus. However, on the lagging strand, replication is discontinuous, requiring multiple RNA primers. When the final RNA primer at the 5′ end of the new strand is removed, it cannot be replaced because DNA polymerase needs a free 3′ OH group to add nucleotides.

在前导链上，第一个引物被放置在模板的 3′ 末端，允许连续合成到染色体末端。然而，在后随链上，复制是不连续的，需要多个 RNA 引物。当新生链 5′ 端最后的 RNA 引物被移除时，它无法被替换，因为 DNA 聚合酶需要自由的 3′ OH 基团来添加核苷酸。

Consequently, each round of DNA replication results in the shortening of the chromosome by the length of the terminal RNA primer—typically 50–200 base pairs per cell division in human somatic cells.

因此，每一轮 DNA 复制都会导致染色体缩短，缩短的长度相当于末端 RNA 引物的长度——在人类体细胞中，每次细胞分裂通常缩短 50–200 个碱基对。

Shortening per division ≈ length of terminal RNA primer (50–200 bp)

每次分裂缩短量 ≈ 末端 RNA 引物的长度（50–200 bp）

This phenomenon, known as the end-replication problem, was first predicted by Alexey Olovnikov in 1971 and later confirmed experimentally. It imposes a finite limit on the number of times a cell can divide.

这种现象称为末端复制问题，由 Alexey Olovnikov 在 1971 年首次预测，随后通过实验证实。它对细胞可以分裂的次数施加了有限的限制。

4. Telomerase: The Enzyme That Counteracts Shortening | 端粒酶：抵消缩短的酶

Telomerase is a ribonucleoprotein enzyme that extends telomeric DNA by adding repetitive TTAGGG sequences to the 3′ end of the chromosome. It is a reverse transcriptase, meaning it uses an RNA template to synthesise DNA.

端粒酶是一种核糖核蛋白酶，通过向染色体 3′ 端添加重复的 TTAGGG 序列来延长端粒 DNA。它是一种逆转录酶，即利用 RNA 模板合成 DNA。

The enzyme consists of two essential components: TERT (telomerase reverse transcriptase), the catalytic protein subunit, and TERC (telomerase RNA component), which contains the template sequence complementary to the telomeric repeat.

该酶由两个必需组分构成：TERT（端粒酶逆转录酶），即催化蛋白亚基；以及 TERC（端粒酶 RNA 组分），其包含与端粒重复序列互补的模板序列。

Human telomerase template: 3′-AAUCCC-5′ → synthesises 5′-TTAGGG-3′

人类端粒酶模板：3′-AAUCCC-5′ → 合成 5′-TTAGGG-3′

The mechanism of action involves repeated cycles of binding, nucleotide addition, and translocation. First, the telomerase RNA template base-pairs with the single-stranded overhang at the chromosome end. Then, the reverse transcriptase activity adds nucleotides complementary to the RNA template. Finally, the enzyme translocates to the new end and repeats the process, lengthening the telomere.

其作用机制包括结合、核苷酸添加和转位的重复循环。首先，端粒酶 RNA 模板与染色体末端的单链突出端碱基配对。然后，逆转录酶活性添加与 RNA 模板互补的核苷酸。最后，酶转位到新的末端并重复该过程，从而延长端粒。

It is important to note that telomerase is not the only mechanism maintaining telomere length. Some cancer cells use the alternative lengthening of telomeres (ALT) pathway, which relies on homologous recombination between telomeric repeats.

值得注意的是，端粒酶并不是维持端粒长度的唯一机制。一些癌细胞使用端粒替代延长（ALT）途径，该途径依赖于端粒重复序列之间的同源重组。

5. Telomere Shortening and Cellular Senescence | 端粒缩短与细胞衰老

In most somatic cells, telomerase is not expressed at functional levels. As a result, telomeres shorten with each mitotic division. When telomeres become critically short, they trigger a DNA damage response that leads to replicative senescence—the permanent cessation of cell division.

在大多数体细胞中，端粒酶不以功能性水平表达。因此，端粒随每次有丝分裂而缩短。当端粒变得过短时，它们触发 DNA 损伤应答，导致复制性衰老——细胞分裂的永久性停止。

Leonard Hayflick discovered in 1961 that human fibroblasts cultured in the laboratory divide only a finite number of times (approximately 50–70 divisions) before halting. This limit, now known as the Hayflick limit, is directly correlated with telomere length.

Leonard Hayflick 在 1961 年发现，实验室培养的人成纤维细胞在停止前只能分裂有限次数（约 50–70 次）。这个极限，即今天所称的 Hayflick 极限，与端粒长度直接相关。

Critically short telomeres are recognised by the cell as DNA double-strand breaks. This activates the p53 pathway, leading to upregulation of p21 and subsequent cell cycle arrest at the G1 checkpoint. Alternatively, activation of the Rb pathway can also induce senescence.

过短的端粒被细胞识别为 DNA 双链断裂。这激活 p53 通路，导致 p21 上调，进而使细胞周期阻滞在 G1 检查点。或者，Rb 通路的激活也可诱导衰老。

Senescence is not merely a cellular endpoint; it is an important tumour suppressor mechanism. By preventing damaged or aged cells from dividing further, the risk of malignant transformation is reduced.

衰老不仅仅是细胞的终点；它是一种重要的肿瘤抑制机制。通过阻止受损或老化的细胞进一步分裂，恶性转化的风险得以降低。

6. Telomeres in Germ Cells and Stem Cells | 生殖细胞与干细胞中的端粒

Germ cells, embryonic stem cells, and adult somatic stem cells maintain high telomerase activity. This ensures that telomere length is preserved across generations and in tissues that require continuous renewal.

生殖细胞、胚胎干细胞和成体体细胞干细胞维持着高水平的端粒酶活性。这确保了端粒长度在世代之间以及需要持续更新的组织中得到保持。

In germ cells, telomerase activity is particularly high, which prevents telomere shortening during meiosis and early embryonic development. This is essential because each generation must inherit chromosomes with sufficiently long telomeres to support the organism’s lifetime of cell division.

在生殖细胞中，端粒酶活性尤其高，这防止了减数分裂和早期胚胎发育期间的端粒缩短。这是必要的，因为每一代都必须遗传足够长的端粒染色体，以支持生物体一生的细胞分裂。

Haematopoietic stem cells, intestinal crypt stem cells, and skin basal layer stem cells all express telomerase, albeit at lower levels than germ cells. This allows them to divide repeatedly for tissue maintenance while undergoing only gradual telomere erosion over time.

造血干细胞、肠道隐窝干细胞和皮肤基底层的干细胞都表达端粒酶，尽管水平低于生殖细胞。这使得它们能够反复分裂以维持组织，同时端粒随时间仅逐渐侵蚀。

However, even in stem cells, telomerase activity is insufficient to maintain absolute telomere length indefinitely. Thus, stem cell function declines with age, contributing to the ageing phenotype.

然而，即使在干细胞中，端粒酶活性也不足以无限期地维持绝对的端粒长度。因此，干细胞功能随年龄增长而下降，从而促进了衰老表型。

7. Telomeres and Cancer | 端粒与癌症

Telomeres play a paradoxical role in cancer biology. On the one hand, telomere shortening acts as a barrier to tumour formation; on the other hand, cancer cells must overcome this barrier to achieve unlimited proliferation.

端粒在癌症生物学中扮演着矛盾的角色。一方面，端粒缩短是肿瘤形成的屏障；另一方面，癌细胞必须克服这一屏障以实现无限增殖。

Approximately 85–90% of human tumours exhibit elevated telomerase activity, enabling them to restore and maintain their telomeres. This is achieved through reactivation of the TERT gene, often via promoter mutations, epigenetic alterations, or amplification.

大约 85–90% 的人类肿瘤表现出升高的端粒酶活性，使其能够恢复并维持端粒。这是通过 TERT 基因的重新激活实现的，通常通过启动子突变、表观遗传改变或基因扩增。

The remaining 10–15% of cancers maintain telomeres via the ALT pathway, which is more common in sarcomas and some gliomas. In ALT cells, telomeres are highly heterogeneous in length and contain partially single-stranded DNA.

其余 10–15% 的癌症通过 ALT 途径维持端粒，这在肉瘤和某些胶质瘤中更为常见。在 ALT 细胞中，端粒长度高度异质，并含有部分单链 DNA。

Telomerase inhibitors have been explored as cancer therapeutics. For example, imetelstat, a lipid-conjugated oligonucleotide that binds to the RNA template of telomerase, has shown promising results in clinical trials for certain haematological malignancies.

端粒酶抑制剂已被探索作为癌症治疗药物。例如，Imetelstat 是一种脂质共轭寡核苷酸，可结合端粒酶的 RNA 模板，在针对某些血液系统恶性肿瘤的临床试验中显示出有希望的结果。

However, targeting telomerase in cancer therapy is complicated by its requirement in normal stem cells. Selective inhibition must therefore balance anti-tumour efficacy against potential toxicity to proliferative tissues.

然而，在癌症治疗中靶向端粒酶因其在正常干细胞中的需求而变得复杂。因此，选择性抑制必须在抗肿瘤疗效与对增殖组织的潜在毒性之间取得平衡。

8. Telomere Length and Human Ageing | 端粒长度与人类衰老

Numerous studies have established a correlation between telomere length and chronological age. In peripheral blood leukocytes, telomere length decreases by approximately 20–40 base pairs per year in adults.

大量研究已建立端粒长度与实际年龄之间的相关性。在外周血白细胞中，成人端粒长度每年减少约 20–40 个碱基对。

Premature ageing syndromes, such as Werner syndrome and dyskeratosis congenita, are associated with excessive telomere shortening. Dyskeratosis congenita, in particular, is caused by mutations in telomerase components (such as TERC or TERT) or shelterin proteins, leading to critically short telomeres and early-onset bone marrow failure, pulmonary fibrosis, and skin abnormalities.

早衰综合征，如 Werner 综合征和先天性角化不良，与过度端粒缩短相关。先天性角化不良尤其由端粒酶组分（如 TERC 或 TERT）或 shelterin 蛋白的突变引起，导致端粒过短以及早发性骨髓衰竭、肺纤维化和皮肤异常。

While shorter telomeres are statistically linked to increased risk of age-related diseases, including cardiovascular disease and type 2 diabetes, it is important to note that correlation does not equal causation. Chronic inflammation and oxidative stress can both shorten telomeres and independently contribute to disease pathology.

虽然较短的端粒在统计学上与年龄相关疾病（包括心血管疾病和 2 型糖尿病）风险增加有关，但必须注意相关性不等于因果关系。慢性炎症和氧化应激既能缩短端粒，又独立促进疾病病理。

Lifestyle factors, such as smoking, obesity, poor diet, and psychological stress, have been associated with accelerated telomere shortening. Conversely, regular exercise and a balanced diet rich in antioxidants may help preserve telomere length, though the causal relationships remain under investigation.

生活方式因素，如吸烟、肥胖、不良饮食和心理压力，已被发现与端粒加速缩短相关。相反，规律运动和富含抗氧化剂的均衡饮食可能有助于维持端粒长度，尽管因果关系仍在研究中。

9. Telomeres and Epigenetics | 端粒与表观遗传学

Telomere length is not solely determined by genetic inheritance; epigenetic modifications also exert significant influence. DNA methylation patterns at subtelomeric regions affect telomere length regulation, likely by modulating the binding of telomere-associated proteins.

端粒长度并不仅仅由遗传决定；表观遗传修饰也产生显著影响。亚端粒区域的 DNA 甲基化模式影响端粒长度调控，可能通过调节端粒相关蛋白的结合来实现。

Histone modifications at telomeres, particularly methylation and acetylation, regulate the accessibility of telomerase to the chromosome end. Additionally, the level of DNA methylation at the TERT promoter influences telomerase expression.

端粒处的组蛋白修饰，特别是甲基化和乙酰化，调节端粒酶对染色体末端的可及性。此外，TERT 启动子处的 DNA 甲基化水平影响端粒酶的表达。

Interestingly, studies have shown that offspring of individuals who experienced famine or severe stress exhibit altered telomere lengths, suggesting transgenerational epigenetic inheritance of telomere status—though this field remains subject to active debate.

有趣的是，研究表明，经历过饥荒或严重压力的个体的后代表现出改变的端粒长度，这表明端粒状态的跨代表观遗传——尽管这一领域仍在激烈争论中。

10. Clinical Applications and Future Directions | 临床应用与未来方向

Telomere biology has opened new avenues for medical diagnostics and therapeutics. Telomere length measurement is used as a biomarker for cellular ageing and disease risk, with quantitative PCR and Southern blotting being the most common methods.

端粒生物学为医学诊断和治疗开辟了新的途径。端粒长度测量被用作细胞衰老和疾病风险的生物标志物，定量 PCR 和 Southern 印迹法是最常用的方法。

Telomerase activation is being explored as a therapeutic strategy for regenerative medicine and age-related diseases. For example, a small molecule called TA-65 has been reported to activate telomerase in vitro and extend telomere length in animal models, although human clinical evidence remains limited.

端粒酶激活正被探索为再生医学和年龄相关疾病的治疗策略。例如，一种名为 TA-65 的小分子据报道可在体外激活端粒酶并在动物模型中延长端粒长度，尽管人类临床证据仍然有限。

Conversely, telomerase inhibition is a candidate strategy for cancer treatment. Several clinical trials are testing telomerase inhibitors in combination with conventional chemotherapy to enhance treatment efficacy.

相反，端粒酶抑制是癌症治疗的候选策略。多项临床试验正在测试端粒酶抑制剂与常规化疗联合使用，以增强治疗效果。

Additionally, telomerase-based vaccines, such as UV1 and GV1001, target telomerase-derived peptides presented on cancer cell surfaces, stimulating the immune system to attack telomerase-positive tumour cells.

此外，基于端粒酶的疫苗，如 UV1 和 GV1001，靶向癌细胞表面呈递的端粒酶衍生肽，刺激免疫系统攻击端粒酶阳性的肿瘤细胞。

Another promising approach involves gene therapy using adeno-associated viruses to deliver TERT to tissues, which has successfully extended lifespan and delayed age-related pathologies in mouse models.

另一个有前景的方法是使用腺相关病毒递送 TERT 基因进行基因治疗，该方法在小鼠模型中成功延长了寿命并延缓了年龄相关病理。

11. Key Concepts for Examination | 考试核心概念总结

For CIE A-Level Biology, the following key points are essential when writing about telomeres:

对于 CIE A-Level 生物学考试，以下关于端粒的要点是写作时的核心内容：

Telomeres consist of repetitive non-coding DNA (TTAGGG in humans) and associated proteins that protect chromosome ends.

端粒由重复的非编码 DNA（人类为 TTAGGG）和伴随蛋白组成，保护染色体末端。
They prevent chromosome fusion, degradation, and the triggering of DNA damage responses.

它们防止染色体融合、降解以及引发 DNA 损伤应答。
The end-replication problem arises because DNA polymerase cannot completely replicate the 5′ ends of linear chromosomes.

末端复制问题源于 DNA 聚合酶无法完整复制线性染色体的 5′ 端。
Telomerase, containing both protein and RNA components, extends telomeres by using its RNA template to synthesise new TTAGGG repeats.

端粒酶包含蛋白质和 RNA 两种组分，利用其 RNA 模板合成新的 TTAGGG 重复序列以延长端粒。
Most somatic cells lack telomerase, so telomeres shorten with each division, eventually triggering replicative senescence.

大多数体细胞缺乏端粒酶，因此端粒随每次分裂而缩短，最终触发复制性衰老。
Germ cells, stem cells, and most cancer cells exhibit high telomerase activity, enabling unlimited or prolonged cell division.

生殖细胞、干细胞和大多数癌细胞表现出高水平的端粒酶活性，从而能够进行无限或延长的细胞分裂。

12. Conclusion | 结论

Telomeres are far more than simple protective caps. They are dynamic regulators of cellular lifespan, genomic stability, and tumour suppression. The intricate balance between telomere shortening, telomerase activity, and cellular senescence underlies fundamental processes of ageing and cancer development.

端粒远不止是简单的保护帽。它们是细胞寿命、基因组稳定性和肿瘤抑制的动态调节者。端粒缩短、端粒酶活性和细胞衰老之间的精密平衡构成了衰老和癌症发展的基本过程。

Understanding telomere biology provides profound insights into how organisms manage the conflict between the need for cell renewal and the risk of cancer. It also reveals why ageing is not simply a passive wearing out of tissues, but an active, regulated process shaped by evolution.

理解端粒生物学为生物体如何管理细胞更新需求与癌症风险之间的冲突提供了深刻的见解。它还揭示了为什么衰老不仅仅是组织的被动耗损，而是一个由进化塑造的主动调节过程。

As research progresses, modulating telomere length and telomerase activity may hold the key to extending healthy lifespan and developing novel cancer therapies. For A-Level students, mastering this topic is not only an examination requirement but also a gateway to understanding contemporary biomedical science.

随着研究的进展，调节端粒长度和端粒酶活性可能成为延长健康寿命和开发新型癌症疗法的关键。对于 A-Level 学生而言，掌握这一主题不仅是考试要求，更是理解当代生物医学科学的门户。

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Telomeres: Their Biological Significance | 端粒的生物学意义