OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.4.9 Regulation of Transcription and Translation Exam Questions
Free OxfordAQA International A Level Biology revision for 3.4.9 Regulation of Transcription and Translation: what you need to know, common mistakes and exam-style questions with answers. Covers DNA methylation, histone acetylation, epigenetics and cancer, RNA interference and types of stem cell.
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About OxfordAQA International A Level Biology 3.4.9 Regulation of Transcription and Translation
This Unit 4 topic explains how gene expression is controlled. You need to explain epigenetic control, where increased methylation of DNA and decreased acetylation of histones reduce transcription without changing the base sequence, and how these changes can be passed on through cell division. You also need to relate abnormal methylation of tumour suppressor genes and oncogenes to cancer, and interpret information on epigenetic treatments. RNA interference using miRNA and siRNA is included, along with stem cell potency and the evaluation of stem cell use in treating disorders. It builds on protein synthesis and mutation and cancer from Units 1 and 2.
What you need to know
- DNA methylation Adding methyl groups to cytosine bases in DNA prevents transcription factors binding, so the gene is not transcribed. Increased methylation silences genes without changing the base sequence.
- Histone acetylation When histones are acetylated, chromatin is less condensed and transcription can occur. Decreased acetylation makes chromatin more condensed, so genes are not transcribed.
- Epigenetics and cancer Increased methylation of tumour suppressor genes switches them off, and decreased methylation of oncogenes switches them on, both leading to uncontrolled cell division. Drugs that reverse these changes may be used in treatment.
- RNA interference Small RNA molecules, siRNA and miRNA, bind to complementary sections of mRNA. This leads to the mRNA being broken down or prevents its translation, so less protein is made.
- Stem cells Totipotent cells can form any cell type and exist only for a limited time in early mammalian embryos. Pluripotent cells form almost any type; multipotent and unipotent cells in mature mammals form a limited number or only one type.
- Evaluating stem cell use Stem cells may treat disorders by replacing damaged cells. Issues include rejection, risk of tumours, and ethical objections to using embryos.
Common mistakes in 3.4.9 Regulation of Transcription and Translation
- Saying methylation changes the base sequence. It adds methyl groups to bases; the sequence is unchanged.
- Getting acetylation the wrong way round. Decreased acetylation inhibits transcription; increased acetylation allows it.
- Saying RNA interference acts on DNA. It acts on mRNA after transcription.
- Confusing totipotent and pluripotent. Totipotent cells can form all cell types, including extra-embryonic tissue; pluripotent cells can form almost all.
Try three 3.4.9 Regulation of Transcription and Translation exam-style questions
1. Explain how increased methylation of a tumour suppressor gene can lead to cancer. (3 marks)
Show the mark scheme answer
Methyl groups prevent transcription factors binding; tumour suppressor gene is not transcribed so its protein is not made; cell division is not slowed and becomes uncontrolled.
2. Describe how siRNA reduces the expression of a gene. (2 marks)
Show the mark scheme answer
siRNA binds to a complementary sequence on mRNA; the mRNA is broken down / cannot be translated.
3. Give one advantage and one disadvantage of using embryonic stem cells to treat disease. (2 marks)
Show the mark scheme answer
Advantage: pluripotent so can form many cell types to replace damaged tissue; disadvantage: ethical issues of destroying embryos, or risk of rejection or tumour formation.
3.4.9 Regulation of Transcription and Translation FAQs
What does OxfordAQA International A Level Biology 3.4.9 Regulation of Transcription and Translation cover?
It covers DNA methylation, histone acetylation, epigenetics and cancer, RNA interference and types of stem cell.
Which unit is 3.4.9 Regulation of Transcription and Translation examined in?
It is part of Unit 4, Control, which is an International A2 paper. The Unit 5 synoptic paper can also draw on this content.
What does epigenetic mean?
Epigenetic changes are heritable changes in gene expression that do not change the DNA base sequence. They include DNA methylation and changes to histone acetylation, and can be influenced by the environment.
