GCSE WJEC Biology: Transcription Explained | GCSE WJEC 生物：转录精讲

📚 GCSE WJEC Biology: Transcription Explained | GCSE WJEC 生物：转录精讲

Transcription is the essential first stage of protein synthesis, copying a gene’s DNA sequence into a portable messenger RNA (mRNA) molecule. Mastering this process is vital for the WJEC GCSE Biology exam, as it connects the stable genetic code in the nucleus to the protein-making machinery in the cytoplasm.

转录是蛋白质合成至关重要的第一阶段，它将基因的DNA序列拷贝到一个可运输的信使RNA（mRNA）分子上。掌握这一过程对WJEC GCSE生物考试至关重要，因为它将细胞核中稳定的遗传密码与细胞质中的蛋白质制造机器连接起来。

1. What is Transcription? | 什么是转录？

Transcription is the enzymatic synthesis of a complementary mRNA strand using one strand of a gene’s DNA as a template. It takes place in the nucleus of eukaryotic cells and marks the beginning of gene expression. The result is a single-stranded RNA molecule that carries the genetic instructions needed to build a polypeptide.

转录是利用基因DNA的一条链作为模板，酶促合成互补mRNA链的过程。它发生在真核细胞的细胞核中，标志着基因表达的开始。其产物是一条单链RNA分子，携带着构建多肽所需的遗传指令。

2. Where Does Transcription Occur? | 转录在哪里发生？

In eukaryotic organisms, transcription occurs inside the membrane-bound nucleus. The DNA remains safely stored in the nucleus, while the newly synthesised mRNA will later exit through nuclear pores to reach ribosomes in the cytoplasm for translation. Keeping transcription and translation separated in space allows RNA processing to take place before the message is read.

在真核生物中，转录发生在有膜包裹的细胞核内部。DNA安全地储存在细胞核内，而新合成的mRNA随后将通过核孔离开，进入细胞质中的核糖体进行翻译。在空间上分隔转录和翻译，使得信息读取前能够进行RNA加工。

3. The DNA Template Strand | DNA 模板链

Only one of the two DNA strands of a gene is used as the transcription template. This strand is called the template strand or antisense strand. Its sequence is complementary to the mRNA produced. The other DNA strand, known as the coding strand or sense strand, has the same sequence as the mRNA (except that thymine is replaced by uracil in RNA).

基因的两条DNA链中只有一条用作转录的模板，这条链称为模板链或反义链。它的序列与生成的mRNA互补。另一条DNA链，称为编码链或有义链，其序列与mRNA相同（只是RNA中的胸腺嘧啶被尿嘧啶取代）。

RNA polymerase reads the template strand in the 3′ to 5′ direction, allowing it to synthesise the mRNA in the 5′ to 3′ direction. This directionality is essential for the correct assembly of nucleotides. For example, if a segment of the template strand reads 3′-TACGGATCG-5′, the resulting mRNA will be 5′-AUGCCUAGC-3′.

RNA聚合酶以3′到5′方向读取模板链，从而使其能以5′到3′方向合成mRNA。这种方向性对于核苷酸的正确组装至关重要。例如，如果一段模板链序列为3′-TACGGATCG-5′，生成的mRNA将是5′-AUGCCUAGC-3′。

4. Role of RNA Polymerase | RNA聚合酶的作用

RNA polymerase is the key enzyme that carries out transcription. It binds to a specific DNA region called the promoter, separates the two DNA strands by breaking hydrogen bonds, and then catalyses the formation of phosphodiester bonds between RNA nucleotides. Unlike DNA polymerase, it does not require a primer to begin synthesis; it can start a new RNA strand from scratch.

RNA聚合酶是执行转录的关键酶。它与DNA上称为启动子的特定区域结合，通过断裂氢键使两条DNA链分开，然后催化RNA核苷酸之间形成磷酸二酯键。与DNA聚合酶不同，它不需要引物就能开始合成，可以从头开始新RNA链的合成。

As RNA polymerase moves along the template, it unwinds the DNA ahead of it and allows the DNA behind to rewind back into a double helix. This maintains the stability of the genome while a gene is being transcribed.

随着RNA聚合酶沿模板链移动，它解开前方的DNA，并让后方的DNA重新绕回双螺旋。这保证了基因被转录时基因组的稳定性。

5. Base-Pairing Rules | 碱基互补配对规则

Transcription follows strict complementary base‑pairing rules, with one important difference from DNA replication: adenine (A) on the DNA template pairs with uracil (U) in RNA, not thymine. Thymine (T) on the template pairs with adenine (A) in RNA. Cytosine (C) pairs with guanine (G), and guanine (G) pairs with cytosine (C).

转录遵循严格的碱基互补配对规则，与DNA复制有一个重要区别：DNA模板上的腺嘌呤（A）与RNA中的尿嘧啶（U）配对，而不是胸腺嘧啶。模板上的胸腺嘧啶（T）与RNA中的腺嘌呤（A）配对。胞嘧啶（C）与鸟嘌呤（G）配对，鸟嘌呤（G）与胞嘧啶（C）配对。

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