Yeast cells sense changes in the glucose concentration around them by using transcription factors to turn genes off. When glucose is present: Mig1 transcription factors attach to the promoters of five genes, and once Mig1 is bound to the promoters, transcription of these genes is switched off (repressed). The genes repressed by Mig1 code for five enzymes that enable yeast cells to metabolise the sugar galactose when glucose is not present.
(a)[3]
Complete Table 5.1 to show three chemical differences between a transcription factor, such as Mig1, and a promoter.
(b(i))[2]
Explain why bioinformatic techniques were used to obtain the information in Table 5.2.
(b(ii))[1]
Identify, with a reason, the yeast cell chromosome that is most likely to contain genes that code for enzymes that metabolise galactose.
(b(iii))[2]
Suggest reasons why an individual diploid yeast cell has a larger number of Mig1-binding promoter sites than the expected number of ten.
(c)[3]
Explain how $Escherichia\ coli$ prevents production of the proteins needed to metabolise lactose sugar.
Worked solution & mark scheme
This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Transcription factor is a protein, promoter is DNA” …