Edexcel IGCSE Biology 3.18B Genes, proteins & phenotype
Practise explaining transcription and translation from genes to proteins in contexts such as GM crops, vaccines and haemoglobin.
- Syllabus
- First assessment 2019
- Course
- Biology 4BI1
Exam points
- describe transcription as DNA unzipping and mRNA copying a gene in the nucleus
- explain translation using ribosomes, codons, tRNA, anticodons and amino acids
- link altered RNA or gene sequences to blocked or changed protein production
3.18B Protein synthesis question 1
[Maximum number: 4]
Apples contain an enzyme called phenol oxidase.
When apple tissue is exposed to oxygen in the air, this enzyme turns the apple tissue brown.
A genetically modified (GM) variety of apple has been produced that does not turn brown when exposed to air.
These apples have a gene in their DNA that produces a section of mRNA with a complementary sequence to the mRNA for the phenol oxidase gene.
Explain why these GM apples do not turn brown when the apple tissue is exposed to air.
Use your knowledge of protein synthesis to support your answer.
An explanation that makes reference to four of the following points:
1. (complementary) RNA binds to the phenol oxidase RNA / eq
2. translation cannot occur
3. so enzyme / phenol oxidase not made
AND
max three from:
4. transcription makes (m)RNA
5. RNA leaves nucleus and enters cytoplasm / RNA moves to ribosome / eq
6. tRNA brings / carries / transports amino acids / eq
7. (during translation) tRNA binds mRNA / anticodons bind codons
8. amino acids join / amino acid chain / makes polypeptide / peptide bonds form / eq
Accept DNA unzips and
(m)RNA is
made
polymerase
makes (m)RNA
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