Factors affecting gene expressionEdexcel A-Level Biology B: Mind map

Exam questions on Factors affecting gene expression

1. A researcher studies a gene in liver cells that is transcribed only when a protein, factor F, enters the nucleus and binds to a DNA sequence next to the gene. In muscle cells factor F is absent and the gene is not transcribed, although muscle cells contain the same gene.
   Explain how factor F can increase the rate of transcription of the gene in liver cells.2 marks
2. The gene for a muscle protein is transcribed in two different tissues. In both tissues the primary transcript has six exons. In tissue 1 the mature mRNA contains exons 1 to 6. In tissue 2 the mature mRNA contains exons 1, 2, 4, 5 and 6, and the protein it codes for is shorter and has a different function.
   Explain why the two mRNA molecules lead to proteins with different functions.2 marks
3. Cells from a tumour show that the promoter region of a tumour suppressor gene has many methyl groups attached to its cytosine bases, and the histones around the gene have had their acetyl groups removed. The tumour suppressor gene is not expressed in these cells.
   Explain how these modifications prevent expression of the tumour suppressor gene.3 marks