基因改造（基因工程）
生物· 5.12–5.16（4BI1 2017年第3版）· 12 分钟阅读
1. 基因工程中使用的酶★★☆☆☆⏱ 2 min
限制酶
可在特定的可识别靶位点切割DNA的酶，用于分离目的基因或者切割载体DNA
DNA连接酶
可封合两段切割后DNA的磷酸脱氧核糖骨架，将二者永久拼接在一起的酶
写出用于从人类DNA中切出人胰岛素基因的酶，并说明其核心功能。
- 1
- 确定正确的酶：限制酶
- 2
- 说明其功能：它在特定靶位点切割DNA，将胰岛素基因从人类基因组中完整分离出来。
Exam tip:
评分标准对这两种酶的区分十分严格：绝对不要写限制酶连接DNA，或者连接酶切割DNA——这是一道常见的1-2分拉分题。
2. 用于重组DNA转移的载体★★☆☆☆⏱ 2 min
载体
将重组DNA送入宿主细胞的结构，使外源基因可以在宿主细胞中完成表达
写出基因工程中可作为载体的两种结构，并分别描述一个使其适合作为载体的特性。
- 1
- 质粒：细菌体内的小型环状DNA，可轻松切开以插入外源DNA，且容易被细菌宿主细胞吸收。
- 2
- 病毒：天然就具备将自身遗传物质插入宿主细胞的特性，因此可被改造为携带重组DNA的载体。
3. 利用转基因细菌生产人胰岛素★★★☆☆⏱ 3 min
Restriction enzyme cuts the desired human insulin gene out of human DNA, and cuts open a bacterial plasmid, leaving matching sticky ends
Ligase enzyme joins the insulin gene into the plasmid, forming recombinant DNA
The plasmid (vector) inserts the recombinant DNA into a host bacterial cell
GM bacteria are grown in large industrial fermenters under optimal conditions, reproducing rapidly and expressing the insulin gene to make insulin protein
Insulin is extracted and purified for medical use by people with diabetes
一道4分考题要求你概述利用转基因细菌生产人胰岛素的流程，列出可拿到满分的关键步骤。
- 1
- 使用限制酶切出人胰岛素基因，同时切开细菌质粒（1分）
- 2
- 使用DNA连接酶将胰岛素基因拼接到质粒中，获得重组DNA（1分）
- 3
- 以质粒作为载体，将重组质粒导入细菌宿主细胞（1分）
- 4
- 在发酵罐中培养转基因细菌，产出大量胰岛素后进行提纯（1分）
Exam tip:
作答时务必按顺序列出所有步骤，并且明确写出两种酶的名称——如果遗漏连接酶或者载体相关步骤会被扣分。
4. 用于提升粮食产量的转基因植物★★★☆☆⏱ 3 min
Common GM crop traits: pest resistance, herbicide resistance, higher yield, added nutrients (e.g. beta-carotene in golden rice), longer shelf life
Key benefits: reduces pesticide use, lowers food costs, reduces malnutrition, improves food security in low-income regions
Key concerns: unknown long-term health effects of consuming GM crops, risk of modified genes spreading to wild plant populations, ethical concerns about corporate control of seed supplies
评估转基因作物在提升全球粮食产量方面的应用，需包含一项优势和一项潜在顾虑。
- 1
- 益处示例：转基因抗虫作物可减少农药使用、提高产量、降低消费者的食品成本，从而在人口增长背景下提升粮食安全水平（2分）
- 2
- 顾虑示例：食用转基因作物的长期健康影响存在不确定性，同时改造后的基因可能扩散到野生植物中，导致生物多样性下降（2分）
- 3
- 平衡结论：转基因作物对粮食安全有显著益处，但需要通过监管管控潜在风险（完成平衡评价得1分）
5. 转基因生物定义★☆☆☆☆⏱ 1 min
转基因
描述一类含有经人工从其他物种转入的遗传物质的生物
解释为什么可生产人胰岛素的转基因细菌属于转基因生物。
- 1
- 给出转基因的定义：如果某一生物携带从其他物种转入的遗传物质，该生物就是转基因生物。
- 2
- 结合示例应用：转基因细菌的DNA中插入了来自人类（其他物种）的人胰岛素基因，因此它们属于转基因生物。
6. 常见陷阱
错误做法:
Mixing up restriction and ligase enzyme roles, stating ligase cuts DNA or restriction joins it
原因:
Mark schemes strictly award marks for correct role assignment, so this error will lose all available marks for enzyme questions
正确做法:
Memorise: Restriction = Cut, Ligase = Join (mnemonic: Restriction Cuts, Ligase Locks)
错误做法:
Only naming plasmids as vectors, forgetting viruses are also valid vectors
原因:
Exam questions often ask for two examples of vectors, so missing viruses will lose half the available marks
正确做法:
Memorise both plasmids and viruses as vector types, with one key feature of each
错误做法:
Using 'recombinant DNA' and 'transgenic' interchangeably
原因:
Recombinant DNA refers to the modified DNA molecule, while transgenic describes the organism carrying cross-species DNA, so the terms are not synonymous
正确做法:
Distinguish explicitly: Recombinant = DNA molecule, Transgenic = organism with DNA from another species
错误做法:
Classifying selective breeding as a type of genetic engineering
原因:
Selective breeding is a traditional, separate technique that does not involve cutting and joining DNA with enzymes, so it is not genetic modification
正确做法:
Only label processes using restriction enzymes, ligase and vectors as genetic engineering
错误做法:
Omitting the fermenter step when describing insulin production
原因:
Fermenters are required to grow large quantities of GM bacteria to produce commercial volumes of insulin, so missing this step loses marks for full process questions
正确做法:
Always include the fermenter culture and insulin purification steps at the end of the insulin production process
7. 速查表
Term/Process | Key Exam Details |
|---|---|
Restriction enzyme | Cuts DNA at specific sites |
Ligase enzyme | Joins/seals pieces of DNA together |
Vectors | Plasmids, viruses: carry recombinant DNA into host cells |
Insulin production steps (order) | Cut gene + plasmid → ligase joins → vector inserts into bacteria → fermenter culture → purify insulin |
GM crop benefits | Pest resistance, higher yield, added nutrients, longer shelf life |
GM crop concerns | Long-term health risk, gene flow to wild plants, ethical concerns |
Transgenic definition | Organism with DNA transferred from a different species |
8. 常见问题
限制酶和DNA连接酶的区别是什么？
限制酶在特定位点切割DNA，而DNA连接酶则将切割后的DNA片段拼接/封合在一起。这是一道常见的2分考题，千万不要混淆二者的功能。
质粒和病毒都属于载体吗？
是的：质粒是细菌体内的小型环状DNA分子，可轻松改造以携带外源DNA；而病毒天然就具备将自身遗传物质插入宿主细胞的特性，因此也可被改造为载体使用。
深入阅读
下一步
Now that you have mastered genetic modification content for Edexcel IGCSE Biology, you can move on to related topics to complete the Use of Biological Resources unit. Next, learn about selective breeding, a traditional alternative to genetic engineering used to produce desired traits in plants and animals. You should also review fermenter operation to ensure you can answer full 6-mark questions on insulin production, and study cloning content for extended answer questions comparing different methods of manipulating biological resources. Practice past paper questions on this topic to familiarise yourself with mark scheme requirements for process and evaluation questions.