📚 Translation | 翻译考点精讲
Translation is the second stage of protein synthesis, where the genetic code carried by messenger RNA (mRNA) is decoded by ribosomes to assemble a specific polypeptide chain. Understanding translation is essential for GCSE AQA Biology, as it explains how cells turn the instructions in DNA into functional proteins such as enzymes, hormones and structural components.
翻译是蛋白质合成的第二阶段，核糖体将信使 RNA（mRNA）携带的遗传密码解码，组装出特定的多肽链。理解翻译对于 GCSE AQA 生物学至关重要，因为它解释了细胞如何将 DNA 中的指令转变为功能性蛋白质，如酶、激素和结构成分。
1. What is Translation? | 什么是翻译？
In biology, translation refers to the process by which ribosomes read the sequence of mRNA bases and use this information to link amino acids together in the correct order. The term ‘translation’ is used because the cell is converting the language of nucleotides (A, U, G, C) into the language of amino acids, the building blocks of proteins.
在生物学中，翻译指的是核糖体读取 mRNA 碱基序列，并利用该信息将氨基酸按正确顺序连接起来的过程。之所以使用“翻译”一词，是因为细胞正在将核苷酸的语言（A、U、G、C）转换为氨基酸的语言，而氨基酸是蛋白质的基本单位。
Translation occurs in the cytoplasm, on ribosomes that may be free-floating or attached to the rough endoplasmic reticulum. This stage follows transcription, where a gene’s DNA sequence is copied into mRNA in the nucleus.
翻译发生在细胞质中的核糖体上，核糖体可以游离在细胞质中，也可以附着在粗面内质网上。这一阶段在转录之后，转录是基因的 DNA 序列在细胞核中被复制成 mRNA 的过程。
2. From DNA to mRNA: A Quick Recap | 从 DNA 到 mRNA：快速回顾
Before translation can begin, the DNA double helix must unwind, and one strand acts as a template for building a complementary mRNA molecule through transcription. In RNA, the base thymine (T) is replaced by uracil (U). This means that where DNA has adenine, mRNA will have uracil, and where DNA has cytosine, mRNA will have guanine, maintaining base-pairing rules.
在翻译开始之前，DNA 双螺旋必须解开，其中一条链作为模板，通过转录构建互补的 mRNA 分子。在 RNA 中，碱基胸腺嘧啶（T）被尿嘧啶（U）取代。这意味着，DNA 中有腺嘌呤的地方，mRNA 中就会有尿嘧啶；DNA 中有胞嘧啶的地方，mRNA 中就会有鸟嘌呤，保持了碱基配对规则。
The mRNA then exits the nucleus through nuclear pores and enters the cytoplasm, where it attaches to a ribosome. The mRNA is single-stranded and carries a series of three-base sequences called codons, each specifying a particular amino acid.
随后，mRNA 通过核孔离开细胞核，进入细胞质，在那里附着到核糖体上。mRNA 是单链的，携带一系列由三个碱基组成的序列，称为密码子，每个密码子对应一种特定的氨基酸。
3. The Role of Ribosomes | 核糖体的作用
Ribosomes are the molecular machines that carry out translation. They are made of ribosomal RNA (rRNA) and proteins, forming two subunits – a small subunit and a large subunit. In GCSE, you need to know that ribosomes provide the site where mRNA and transfer RNA (tRNA) meet, and where peptide bonds form between amino acids.
核糖体是进行翻译的分子机器。它们由核糖体 RNA（rRNA）和蛋白质组成，形成两个亚基——小亚基和大亚基。在 GCSE 中，你需要知道核糖体提供了 mRNA 与转运 RNA（tRNA）相遇的场所，也是氨基酸之间形成肽键的地方。
The small subunit binds to the mRNA, while the large subunit has sites for tRNA molecules to bind. A ribosome can move along the mRNA, reading codons one by one, and catalysing the formation of a growing polypeptide chain.
小亚基与 mRNA 结合，而大亚基上有 tRNA 分子的结合位点。核糖体可以沿着 mRNA 移动，逐个个读取密码子，并催化正在延伸的多肽链的形成。
4. mRNA Structure: Codons | mRNA 结构：密码子
The mRNA strand is a linear sequence of nucleotides containing the bases adenine (A), uracil (U), cytosine (C) and guanine (G). In translation, the sequence is read in groups of three bases, known as codons. Each codon corresponds to either a specific amino acid or a ‘stop’ signal. For example, the codon AUG codes for methionine and often marks the start of translation.
mRNA 链是一条线性的核苷酸序列，含有碱基腺嘌呤（A）、尿嘧啶（U）、胞嘧啶（C）和鸟嘌呤（G）。在翻译过程中，该序列以三个碱基为一组被读取，这些碱基组称为密码子。每个密码子对应一种特定的氨基酸，或是一个“终止”信号。例如，密码子 AUG 编码甲硫氨酸，通常标记翻译的起始点。
The reading of codons is non-overlapping and sequential, meaning the ribosome reads the mRNA three bases at a time, without skipping or re-reading a base. The order of codons determines the order of amino acids in the polypeptide, and thus the protein’s primary structure.
密码子的读取是不重叠且连续的，意味着核糖体一次读取 mRNA 的三个碱基，不会跳过或重复读取某个碱基。密码子的顺序决定了多肽中氨基酸的顺序，进而决定了蛋白质的一级结构。
5. tRNA and Anticodons | tRNA 与反密码子
Transfer RNA (tRNA) is a small, cloverleaf-shaped molecule that acts as an adaptor between the mRNA codon and the corresponding amino acid. Each tRNA molecule has two critical regions: at one end, an anticodon of three unpaired bases that is complementary to a specific mRNA codon; at the other end, an attachment site where the specific amino acid is bound.
转运 RNA（tRNA）是一种小型的三叶草形分子，它充当 mRNA 密码子与相应氨基酸之间的适配器。每个 tRNA 分子有两个关键区域：一端是一个由三个未配对的碱基组成的反密码子，与特定的 mRNA 密码子互补；另一端是一个附着位点，用于结合特定的氨基酸。
During translation, the anticodon of a tRNA molecule base-pairs temporarily with the complementary codon on the mRNA, bringing its amino acid into the correct position on the ribosome. This ensures that amino acids are added in the precise sequence dictated by the mRNA.
在翻译过程中，tRNA 分子的反密码子与 mRNA 上互补的密码子暂时配对，将其携带的氨基酸带到核糖体上的正确位置。这确保了氨基酸按照 mRNA 指定的精确顺序被添加进去。
6. The Genetic Code | 遗传密码
The genetic code is the set of rules by which information encoded in mRNA is translated into proteins. It is described as degenerate because most amino acids are encoded by more than one codon. For instance, the amino acid leucine can be specified by UUA, UUG, CUU, CUC, CUA or CUG. The code is also universal, meaning the same codon specifies the same amino acid across nearly all organisms.
遗传密码是将 mRNA 中编码的信息翻译成蛋白质的一套规则。它具有简并性，因为大多数氨基酸由不止一个密码子编码。例如，氨基酸亮氨酸可由 UUA、UUG、CUU、CUC、CUA 或 CUG 指定。密码子还具有通用性，即几乎所有生物中相同的密码子都指定相同的氨基酸。
There are three stop codons (UAA, UAG, UGA) that do not code for any amino acid but signal the end of translation. The start codon AUG codes for methionine and initiates the process.
存在三个终止密码子（UAA、UAG、UGA），它们不编码任何氨基酸，但发出翻译终止的信号。起始密码子 AUG 编码甲硫氨酸，并启动该过程。
The table below shows a simplified example of how codons specify amino acids (note: the full table includes 64 codons).
下表展示了密码子如何指定氨基酸的简化示例（注意：完整密码子表包含 64 个密码子）。
| Codon | Amino Acid |
|---|---|
| AUG | Methionine (Start) |
| UUU, UUC | Phenylalanine |
| GGU, GGC, GGA, GGG | Glycine |
| UAA, UAG, UGA | Stop |
7. Initiation of Translation | 翻译的起始
Translation begins when the small ribosomal subunit binds to the mRNA near the 5′ end. The ribosome scans along the mRNA until it encounters the start codon, AUG. A specific tRNA carrying methionine (with the anticodon UAC) base-pairs with this start codon. The large ribosomal subunit then joins to form a complete ribosome, and the methionine-tRNA occupies one of the binding sites (the P site).
翻译开始时，核糖体小亚基结合到 mRNA 靠近 5′ 端的位置。核糖体沿 mRNA 扫描，直到遇到起始密码子 AUG。一个携带着甲硫氨酸的特殊 tRNA（反密码子为 UAC）与这个起始密码子碱基配对。接着，大亚基加入形成完整的核糖体，甲硫氨酸-tRNA 占据其中一个结合位点（P 位点）。
This initiation complex sets the reading frame so that all subsequent codons are read in groups of three from that point. In eukaryotes, initiation also involves several protein factors, but for GCSE AQA, remembering the binding of the ribosome and the first tRNA is sufficient.
这种起始复合物设定了阅读框，使得随后所有的密码子都从这一点开始按三个一组读取。在真核生物中，起始还涉及多种蛋白质因子，但对 GCSE AQA 而言，记住核糖体与第一个 tRNA 的结合就足够了。
8. Elongation: Building the Polypeptide | 延伸：构建多肽链
After initiation, the ribosome moves along the mRNA in the 5′ to 3′ direction, a process called translocation. The ribosome has three binding sites for tRNA: the A (aminoacyl), P (peptidyl) and E (exit) sites. A tRNA carrying the next amino acid enters the A site, and its anticodon must match the codon on the mRNA.
起始之后，核糖体沿 mRNA 从 5′ 端向 3′ 端移动，这一过程称为移位。核糖体有三个 tRNA 结合位点：A 位点（氨酰位点）、P 位点（肽基位点）和 E 位点（出口位点）。携带着下一个氨基酸的 tRNA 进入 A 位点，其反密码子必须与 mRNA 上的密码子匹配。
Once the correct tRNA is in place, a peptide bond forms between the amino acid at the P site and the amino acid at the A site, catalysed by peptidyl transferase activity of the ribosome (which in GCSE is described simply as ‘the ribosome catalyses the formation of a peptide bond’). The ribosome then shifts one codon forward, moving the uncharged tRNA into the E site, where it exits, and the peptide-bearing tRNA into the P site, freeing the A site for the next tRNA.
一旦正确的 tRNA 就位，P 位点的氨基酸与 A 位点的氨基酸之间就会形成一个肽键，这一过程由核糖体的肽基转移酶活性催化（在 GCSE 中，简单描述为“核糖体催化肽键的形成”）。接着，核糖体向前移动一个密码子，将空载的 tRNA 移至 E 位点并排出，将携带肽链的 tRNA 移至 P 位点，空出 A 位点供下一个 tRNA 进入。
This process repeats, adding amino acids one by one to the growing polypeptide chain. The precise matching between codons and anticodons ensures the sequence of amino acids follows the original gene sequence.
这个过程不断重复，将氨基酸一个接一个地添加到正在延长的多肽链上。密码子与反密码子之间的精确匹配确保了氨基酸序列与原始基因序列一致。
9. Termination of Translation | 翻译的终止
Elongation continues until the ribosome reaches a stop codon (UAA, UAG, or UGA) on the mRNA. No tRNA molecules have anticodons complementary to these codons. Instead, proteins called release factors bind to the stop codon, triggering the ribosome to release the completed polypeptide chain. The ribosomal subunits then dissociate from the mRNA and can be reused for another round of translation.
延伸持续进行，直到核糖体在 mRNA 上遇到终止密码子（UAA、UAG 或 UGA）。没有任何 tRNA 分子具有与这些密码子互补的反密码子。相反，被称为释放因子的蛋白质会与终止密码子结合，促使核糖体释放已完成的多肽链。随后，核糖体亚基从 mRNA 上解离，并可被重新用于下一轮翻译。
In GCSE exams, it is important to state that a stop codon does not code for an amino acid and that it signals the end of the polypeptide sequence. The newly released polypeptide then folds into its specific three-dimensional shape to become a functional protein.
在 GCSE 考试中，重要的是说明终止密码子不编码任何氨基酸，它发出多肽序列结束的信号。新释放的多肽随后折叠成其特定的三维形状，成为有功能的蛋白质。
10. The Final Product: Polypeptide Folding | 最终产物：多肽折叠
Although translation produces a linear sequence of amino acids (the primary structure), a protein’s function depends on its specific shape. The polypeptide chain folds spontaneously, driven by interactions such as hydrogen bonds, ionic bonds and disulphide bridges between R-groups of amino acids. This folding results in secondary structures (alpha-helices and beta-pleated sheets) and a tertiary structure unique to each protein.
尽管翻译产生的是线性的氨基酸序列（一级结构），蛋白质的功能却取决于其特定的形状。多肽链会自发折叠，驱动力来自氨基酸 R 基团之间的氢键、离子键和二硫键等相互作用。这种折叠产生二级结构（α-螺旋和 β-折叠片）以及每种蛋白质特有的三级结构。
Some proteins, like haemoglobin, are made of more than one polypeptide chain, giving them a quaternary structure. Errors in translation can result in a misfolded protein that may not function correctly, which can lead to disease.
有些蛋白质，如血红蛋白，由多条多肽链组成，具有四级结构。翻译中的错误可能导致蛋白质错误折叠，无法正常发挥功能，进而引发疾病。
11. Comparison: Transcription vs Translation | 对比：转录与翻译
Transcription and translation are the two main steps of protein synthesis, but they occur in different locations and produce different molecules. Transcription takes place in the nucleus, where DNA is used to synthesise mRNA. Translation occurs in the cytoplasm, where mRNA is used to synthesise a polypeptide. Transcription uses RNA polymerase to link RNA nucleotides, while translation uses ribosomes, tRNA and amino acids.
转录和翻译是蛋白质合成的两个主要步骤，但它们发生在不同的位置并产生不同的分子。转录在细胞核中进行，以 DNA 为模板合成 mRNA。翻译则在细胞质中进行，以 mRNA 为模板合成多肽。转录利用 RNA 聚合酶连接 RNA 核苷酸，而翻译则利用核糖体、tRNA 和氨基酸。
Another key difference is the language: transcription keeps the information as nucleotide sequences (DNA → RNA), whereas translation converts the nucleotide language into amino acid language. Both processes are essential for gene expression, and a mistake in either can alter the final protein.
另一个关键区别是信息语言：转录将信息保持为核苷酸序列的形式（DNA → RNA），而翻译则将核苷酸语言转换为氨基酸语言。这两个过程对于基因表达都是必不可少的，其中任何一个出错都可能改变最终的蛋白质。
| Feature | Transcription | Translation |
|---|---|---|
| Location | Nucleus | Cytoplasm (ribosomes) |
| Template | DNA | mRNA |
| Product | mRNA | Polypeptide |
| Key molecules | RNA polymerase, nucleotides | Ribosomes, tRNA, amino acids |
| Base pairing | DNA A-U, T-A, C-G, G-C | Codon-anticodon (A-U, C-G) |
12. Exam Tips and Common Mistakes | 考试技巧与常见错误
When answering exam questions on translation, precision with terminology is vital. Use ‘codon’ for mRNA triplets and ‘anticodon’ for tRNA triplets; do not confuse the two. Remember that translation occurs on ribosomes in the cytoplasm, not in the nucleus. Never state that amino acids form new codons – amino acids are not nucleotides.
在回答关于翻译的考试问题时，术语的准确性至关重要。对 mRNA 的三联体使用“密码子”，对 tRNA 的三联体使用“反密码子”；不要将两者混淆。记住，翻译发生在细胞质的核糖体上，而不是细胞核中。绝对不能说氨基酸形成新的密码子——氨基酸不是核苷酸。
A common mistake is to say that the ribosome reads the DNA directly or that tRNA brings nucleotides to the ribosome. Always refer to the flow of information: DNA → mRNA → codon → anticodon → amino acid. Also, be sure to mention peptide bonds when describing how the polypeptide chain is elongated.
一个常见的错误是说核糖体直接读取 DNA，或者说 tRNA 把核苷酸带到核糖体上。始终要提及信息流的顺序：DNA → mRNA → 密码子 → 反密码子 → 氨基酸。此外，在描述多肽链如何延长时，一定要提及肽键。
In longer-answer questions, candidates often forget to describe the role of the stop codon and the release factors. Practice naming the start codon (AUG) and explaining that it codes for methionine. Drawing a simple, labelled diagram of the ribosome with mRNA, tRNA and amino acids can also help secure marks.
在较长的问答题中，考生经常忘记描述终止密码子和释放因子的作用。练习说出起始密码子（AUG），并解释它编码甲硫氨酸。画一个带有 mRNA、tRNA 和氨基酸的简单标注图也能帮助获得分数。
Finally, always link translation to protein function and why proteins are important – enzymes, antibodies, structural components. This context helps secure top marks by demonstrating a broader understanding.
最后，务必将翻译与蛋白质的功能以及蛋白质的重要性联系起来——酶、抗体、结构成分等。这种联系可以展示更广泛的理解，从而帮助获得高分。
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