Golden rice is a genetically engineered crop plant that produces beta-carotene, a substance the human body converts into vitamin A. Scientists inserted a gene from maize into the rice genome to achieve this. Explain how genetic engineering is used to insert a gene from one organism into another organism, and explain why the inserted gene is able to function in the new organism.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Vitamin A deficiency affects millions of people worldwide and can cause blindness. Golden rice was developed to help address this problem by engineering rice plants to produce beta-carotene in their grain.
Model answer (5 marks)
1. A restriction enzyme cuts the donor DNA to release the beta‑carotene gene.
2. The same enzyme cuts the host DNA or a plasmid vector, creating complementary sticky ends.
3. DNA ligase joins the gene into the vector or host DNA, forming recombinant DNA.
4. The recombinant DNA is introduced into rice cells, where it integrates into the genome.
5. Because the genetic code is universal, the inserted gene is transcribed and translated correctly in rice, producing beta‑carotene.
2. The same enzyme cuts the host DNA or a plasmid vector, creating complementary sticky ends.
3. DNA ligase joins the gene into the vector or host DNA, forming recombinant DNA.
4. The recombinant DNA is introduced into rice cells, where it integrates into the genome.
5. Because the genetic code is universal, the inserted gene is transcribed and translated correctly in rice, producing beta‑carotene.
Examiner tips
- Use the sequence of steps (cut, ligate, insert) to structure the answer; include the role of restriction enzyme, ligase, and vector.
- Mention the universality of the genetic code to justify functionality in the new host.
Common mistakes
- Confusing restriction enzyme with ligase; forgetting to mention sticky ends.
- Failing to explain why the gene works in rice (omitting the universal genetic code).
Mark scheme (5 marks)
- A restriction enzyme is used to cut out the desired gene (beta-carotene gene) from the donor organism's DNA
- The same restriction enzyme is used to cut open the host organism's DNA / vector (e.g. plasmid), leaving complementary sticky ends
- Ligase enzyme joins / seals the gene into the host DNA / vector
- The recombinant DNA / vector is inserted into the host organism's cells so the gene becomes part of the host genome
- The genetic code / DNA is universal, so the same codons code for the same amino acids in all organisms, allowing the gene to be transcribed and translated correctly in the new host
Key terms in this question
genome · gene · genetic engineering
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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