Gene Expression for GCSE Edexcel Biology | GCSE Edexcel 生物：基因表达考点精讲

📚 Gene Expression for GCSE Edexcel Biology | GCSE Edexcel 生物：基因表达考点精讲

Gene expression is a fundamental process in living organisms where the genetic code in DNA is used to produce proteins. Understanding how genes are switched on to make specific proteins is essential for GCSE Edexcel Biology, linking DNA structure, protein synthesis, mutations, and variation. This revision guide breaks down every key concept you need to master, from transcription to translation, the genetic code, mutations, and how the environment can influence traits.

基因表达是生物体利用 DNA 中的遗传密码产生蛋白质的基本过程。理解基因如何被“开启”以制造特定的蛋白质，对于 GCSE Edexcel 生物学至关重要，它将 DNA 结构、蛋白质合成、突变和变异等知识串联起来。这份考点精讲将分解你需要掌握的所有关键概念，从转录到翻译、遗传密码、突变以及环境如何影响性状。

1. What is Gene Expression? | 什么是基因表达？

Gene expression is the process by which the information stored in a gene is used to synthesise a functional gene product, usually a protein. Not all genes are expressed at all times; certain genes are turned on or off depending on the cell type and the organism’s needs.

基因表达是指利用储存在基因中的信息来合成功能性基因产物（通常是蛋白质）的过程。并非所有基因都时刻表达；某些基因会根据细胞类型和生物体的需求而被开启或关闭。

Proteins carry out most of the work in cells, including acting as enzymes, hormones, structural components, and antibodies. Therefore, gene expression ultimately determines an organism’s traits, or phenotype.

蛋白质承担了细胞中的大部分工作，包括作为酶、激素、结构组分和抗体。因此，基因表达最终决定了一个生物体的性状，即表型。

The two main stages of gene expression are transcription (in the nucleus) and translation (at ribosomes in the cytoplasm).

基因表达的两个主要阶段是转录（在细胞核中）和翻译（在细胞质中的核糖体上进行）。

2. DNA and Genes: The Blueprint | DNA 和基因：生命蓝图

Deoxyribonucleic acid (DNA) is a double-stranded polymer made of nucleotides. Each nucleotide consists of a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The two strands are held together by complementary base pairing: A pairs with T, and C pairs with G.

脱氧核糖核酸 (DNA) 是由核苷酸组成的双链聚合物。每个核苷酸包含一个脱氧核糖、一个磷酸基团以及四种含氮碱基之一：腺嘌呤 (A)、胸腺嘧啶 (T)、胞嘧啶 (C) 和鸟嘌呤 (G)。两条链通过互补碱基配对结合在一起：A 与 T 配对，C 与 G 配对。

A gene is a specific sequence of bases along a DNA molecule that codes for a particular protein. The order of bases determines the sequence of amino acids in that protein. Each set of three bases (a triplet) codes for one amino acid.

基因是 DNA 分子上一段特定的碱基序列，负责编码某种特定的蛋白质。碱基的顺序决定了该蛋白质中氨基酸的序列。每三个碱基（一个三联体）编码一个氨基酸。

The entire set of genetic material in an organism is called the genome. In humans, the genome is distributed across 46 chromosomes inside the nucleus.

生物体的整套遗传物质称为基因组。人类的基因组分布在细胞核内的 46 条染色体上。

3. Transcription: Copying the Code | 转录：复制密码

Transcription takes place in the nucleus. The double helix of DNA unwinds and unzips at the gene being expressed, exposing the bases on the template strand.

转录发生在细胞核中。DNA 双螺旋在要表达的基因处解旋并解开，暴露出模板链上的碱基。

An enzyme called RNA polymerase moves along the template strand and assembles a complementary single-stranded molecule called messenger RNA (mRNA). In RNA, the base uracil (U) replaces thymine, so adenine on DNA pairs with uracil on mRNA. The pairing rules are: DNA A → mRNA U, DNA T → mRNA A, DNA C → mRNA G, DNA G → mRNA C.

一种叫做 RNA 聚合酶的酶沿着模板链移动，并组装一条互补的单链分子，称为信使 RNA (mRNA)。在 RNA 中，碱基尿嘧啶 (U) 代替了胸腺嘧啶，因此 DNA 上的腺嘌呤与 mRNA 上的尿嘧啶配对。配对规则为：DNA A → mRNA U，DNA T → mRNA A，DNA C → mRNA G，DNA G → mRNA C。

Once the mRNA strand is complete, it detaches from the DNA and the DNA rewinds. The mRNA molecule then exits the nucleus through a nuclear pore and travels to a ribosome in the cytoplasm.

一旦 mRNA 链完成，它就会从 DNA 上脱离，DNA 重新缠绕。然后 mRNA 分子通过核孔离开细胞核，前往细胞质中的核糖体。

For example, if a section of template DNA reads TAC GGA CTA, the resulting mRNA sequence will be AUG CCU GAU.

例如，如果一段模板 DNA 的序列为 TAC GGA CTA，那么产生的 mRNA 序列将是 AUG CCU GAU。

4. Translation: Building the Protein | 翻译：构建蛋白质

Translation occurs at the ribosomes in the cytoplasm. The mRNA attaches to a ribosome, and the ribosome reads the mRNA sequence one codon (three bases) at a time.

翻译发生在细胞质的核糖体上。mRNA 附着在核糖体上，核糖体一次读取一个密码子（三个碱基）。

Transfer RNA (tRNA) molecules carry specific amino acids and have an anticodon — a triplet of bases complementary to the mRNA codon. A tRNA with a complementary anticodon binds to the mRNA codon, bringing its amino acid to the ribosome.

转运 RNA (tRNA) 分子携带特定的氨基酸，并具有一个反密码子——一段与 mRNA 密码子互补的三个碱基。带有互补反密码子的 tRNA 与 mRNA 密码子结合，将其氨基酸带到核糖体上。

As the ribosome moves along the mRNA, amino acids are joined together by peptide bonds to form a polypeptide chain. The order of codons on the mRNA determines the sequence of amino acids, which in turn determines the protein’s shape and function.

随着核糖体沿 mRNA 移动，氨基酸通过肽键连接在一起，形成一条多肽链。mRNA 上密码子的顺序决定了氨基酸的序列，进而决定了蛋白质的形状和功能。

The process continues until a stop codon (e.g., UAA, UAG, UGA) is reached. The completed polypeptide chain then folds into a specific three-dimensional shape to become a functional protein.

该过程一直持续到遇到终止密码子（如 UAA、UAG、UGA）为止。然后完整的多肽链折叠成特定的三维形状，成为有功能的蛋白质。

5. The Genetic Code and Codons | 遗传密码与密码子

The genetic code is the set of rules by which information in mRNA is translated into amino acids. Each codon consists of three mRNA bases and codes for one amino acid. Some amino acids are specified by more than one codon — this is called the degeneracy of the code.

遗传密码是将 mRNA 中的信息翻译成氨基酸的一套规则。每个密码子由三个 mRNA 碱基组成，编码一个氨基酸。有些氨基酸由多个密码子编码，这称为密码的简并性。

The genetic code is universal across almost all living organisms, which is evidence for evolution. That means the codon AUG codes for methionine in bacteria, plants, and humans. AUG is also the standard start codon, signalling the beginning of translation.

遗传密码在几乎所有生物体中都是通用的，这是进化的证据。这意味着密码子 AUG 在细菌、植物和人类中都编码甲硫氨酸。AUG 也是标准的起始密码子，标志着翻译的开始。

Below is a simplified codon table showing a few examples, with corresponding amino acids:

下面是一个简化的密码子表，展示了一些例子及对应的氨基酸：

mRNA Codon	Amino Acid	mRNA Codon	Amino Acid
AUG	Methionine (start)	UUU	Phenylalanine
GGU	Glycine	CCA	Proline
UCA	Serine	UAA, UAG, UGA	Stop

Understanding the codon table allows you to predict the amino acid sequence from a given mRNA strand, a common exam question.

理解密码子表可以帮助你从给定的 mRNA 链推测氨基酸序列，这是常见的考题类型。

6. Mutations: Changes in DNA | 突变：DNA 的改变

A mutation is a random change in the sequence of bases in DNA. Mutations can occur spontaneously during DNA replication or be caused by mutagens such as ionising radiation (UV, X‑rays) and certain chemicals. Mutations happen continuously, but cells have repair mechanisms to correct many of them.

突变是指 DNA 碱基序列发生的随机改变。突变可以在 DNA 复制过程中自发产生，也可能由诱变剂引起，如电离辐射（紫外线、X 射线）和某些化学物质。突变不断发生，但细胞有修复机制来纠正其中的许多错误。

There are three main types of gene mutation:

基因突变主要有三种类型：

Substitution – one base is replaced by another. This may change only one codon and sometimes does not alter the amino acid (silent mutation) due to the degenerate code.
替代 – 一个碱基被另一个碱基替代。可能只改变一个密码子，有时由于密码简并性并不会改变氨基酸（沉默突变）。
Insertion – an extra base is added into the sequence. This shifts the reading frame of the entire gene (frameshift), usually changing all subsequent amino acids.
插入 – 序列中插入一个额外的碱基。这会改变整个基因的阅读框（移码），通常会改变之后所有的氨基酸。
Deletion – a base is removed. Like insertion, this causes a frameshift, resulting in a completely different and often non‑functional protein.
缺失 – 一个碱基被删除。与插入类似，会导致移码，产生完全不同的、通常是无功能的蛋白质。

7. Effects of Mutations on Protein Structure | 突变对蛋白质结构的影响

The effect of a mutation depends on the type of mutation and its location within the gene. A substitution may lead to a single amino acid change, which can be harmless, beneficial, or harmful depending on the protein’s role. For example, sickle cell anaemia is caused by a substitution that changes glutamic acid to valine in haemoglobin.

突变的影响取决于突变的类型及其在基因中的位置。替代可能导致单个氨基酸改变，根据蛋白质的功能，这可能是无害的、有益的或有害的。例如，镰刀型细胞贫血病就是由一种替代引起的，它使血红蛋白中的谷氨酸变为缬氨酸。

Frameshift mutations (insertions and deletions) are usually more serious because they alter every codon from the mutation point onwards, producing a truncated or malfunctioning protein. This can result in genetic disorders or non‑viable cells.

移码突变（插入和缺失）通常更为严重，因为它们会改变从突变点开始之后的每一个密码子，产生截短的或无功能的蛋白质。这可能导致遗传病或细胞无法存活。

Some mutations provide an advantage. For instance, a mutation giving bacteria resistance to an antibiotic can be selected for by natural selection, illustrating the role of mutations in evolution.

有些突变可以提供优势。例如，使细菌对抗生素产生抗性的突变可以被自然选择保留下来，这说明了突变在进化中的作用。

It is important to note that not all mutations alter phenotype; an organism’s phenotype is the result of the combined effects of genotype and environment.

需要注意的是，并非所有突变都会改变表型；生物体的表型是基因型和环境共同作用的结果。

8. Alleles and Phenotype | 等位基因与表型

An allele is a variant form of a gene. Most genes have two alleles in a diploid organism, one inherited from each parent. Different alleles have slightly different base sequences, which can lead to the production of different versions of a protein or different amounts of protein.

等位基因是基因的变体形式。在二倍体生物中，大多数基因有两个等位基因，分别遗传自父母双方。不同的等位基因具有略微不同的碱基序列，这可能导致产生不同版本的蛋白质或不同数量的蛋白质。

The observable characteristics of an organism — its phenotype — are determined by the combination of alleles it possesses (genotype) and environmental influences. For example, the allele for brown eyes codes for a protein that produces melanin pigment; a different allele may produce no melanin, leading to blue eyes.

生物体可观察到的特征——即表型——由其拥有的等位基因组合（基因型）和环境的影响共同决定。例如，棕色眼睛的等位基因编码一种产生黑色素的蛋白质；不同的等位基因可能不产生黑色素，从而导致蓝色眼睛。

Homozygous dominant and heterozygous individuals may express the same phenotype due to dominance. A recessive allele is only expressed in the phenotype when an organism is homozygous recessive.

由于显性作用，显性纯合子和杂合子个体可能表现出相同的表型。只有当生物体为隐性纯合子时，隐性等位基因才会在表型中表达。

The relationship between genotype, protein function, and phenotype is a key theme in genetics. For example, in cystic fibrosis, a recessive allele produces a faulty CFTR protein, affecting chloride ion transport and leading to thick mucus production.

基因型、蛋白质功能与表型之间的关系是遗传学的一个核心主题。例如，在囊性纤维化病中，一个隐性等位基因产生有缺陷的 CFTR 蛋白，影响氯离子转运，导致黏液变稠。

9. Environmental Influences on Gene Expression | 环境对基因表达的影响

An organism’s phenotype is not determined solely by its genes. Environmental factors can also influence gene expression. Temperature, light, nutrition, pH, and oxygen levels can all affect how genes are expressed and how proteins function.

生物体的表型并非仅由基因决定。环境因素也能影响基因表达。温度、光照、营养、pH 和氧气水平都可以影响基因的表达方式以及蛋白质的功能。

For example, in Siamese cats and Himalayan rabbits, the gene for dark fur pigment is only expressed in cooler parts of the body (ears, nose, paws). The enzyme responsible for melanin production is temperature‑sensitive and inactive at higher core temperatures.

例如，在暹罗猫和喜马拉雅兔中，深色皮毛基因只在身体较冷的部位（耳、鼻、爪）表达。负责产生黑色素的酶是温度敏感的，在较高的核心体温下会失活。

In plants, the height or colour of petals can be influenced by the availability of sunlight and mineral nutrients. Identical twins raised in different environments develop distinct phenotypes despite sharing the same DNA.

在植物中，花瓣的高度或颜色会受到阳光和矿质营养可用性的影响。在不同环境中长大的同卵双胞胎尽管拥有相同的 DNA，却会发展出不同的表型。

These examples illustrate that gene expression is flexible and regulated by both internal and external signals, enabling organisms to adapt to their surroundings.

这些例子说明，基因表达是灵活的，并受内部和外部信号的调控，使生物体能够适应周围环境。

10. Exam Tips and Common Misconceptions | 考试技巧与常见误区

To succeed in Edexcel GCSE Biology questions on gene expression, keep the following points in mind:

要在 Edexcel GCSE 生物学的基因表达题目中取得成功，请牢记以下几点：

Always use the correct terminology: transcription produces mRNA, translation produces a polypeptide. Do not say that ‘DNA turns into mRNA’ or that ‘DNA unzips and ribosomes copy it’.
始终使用正确的术语：转录产生 mRNA，翻译产生多肽。不要说“DNA 变成 mRNA”或“DNA 解开，核糖体复制它”。
Be precise about base pairing: in transcription, A on DNA pairs with U on mRNA. In DNA replication, A pairs with T.
碱基配对要准确：在转录中，DNA 上的 A 与 mRNA 上的 U 配对。在 DNA 复制中，A 与 T 配对。
When explaining the effect of a mutation, refer to changes in the amino acid sequence and how this alters the protein’s folding and function.
在解释突变的影响时，要联系到氨基酸序列的改变，以及这如何改变蛋白质的折叠和功能。
Do not confuse codons (on mRNA) with anticodons (on tRNA). The ribosome reads codons; tRNA carries anticodons.
不要混淆密码子（位于 mRNA 上）和反密码子（位于 tRNA 上）。核糖体读取密码子；tRNA 携带反密码子。
Remember that a phenotype is the outcome of genotype + environment. An organism can have a gene for a trait but not express it due to environmental conditions.
记住，表型 = 基因型 + 环境。生物体可能有某种性状的基因，但由于环境条件而没有表达。
Practice using the codon table to translate mRNA into amino acids, and be prepared for questions that provide a DNA template strand and ask for the mRNA sequence and amino acid result.
练习使用密码子表将 mRNA 翻译成氨基酸，并准备好回答给出 DNA 模板链并要求写出 mRNA 序列及氨基酸结果的题目。

Common pitfalls include mixing up the roles of mRNA and tRNA, forgetting that uracil is in RNA, and assuming all mutations are harmful. Mutations provide the raw genetic variation on which natural selection acts.

常见误区包括混淆 mRNA 和 tRNA 的作用，忘记尿嘧啶存在于 RNA 中，以及假设所有突变都是有害的。突变提供了自然选择作用于其上的原始遗传变异。

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Gene Expression for GCSE Edexcel Biology | GCSE Edexcel 生物：基因表达考点精讲