8. (4pts) You are interested in the regulation of a gene that regulates cartilag

Question

8. (4pts) You are interested in the regulation of a gene that regulates cartilage production in joints, gene Crt. You find three proteins that regulate gene Crt expression. Protein A, B and C bind the promoter of the Crt gene to increase or decrease transcription of Crt. Proteins A and B both bind to site 1 but cannot bind to site 1 at the same time. Protein C binds to site 2 on the promoter. Transcriptional start site mRNA of gene Crt You design an in vitro transcription system that contains RNA polymerase, nucleotides, and the gene above. You add various combinations of regulator A, B and C and measure if Crt mRNA is made. The table below shows your results Experiment Regulator ARegulator BRegulator CCrt mRNA roduction Added added added no no es es no es es es 4 A. Which proteins function as transcriptional activators? B. Which proteins function as transcriptional repressors? C. Your advisor wants to know whether regulator A or B binds more strongly to site A. You predict that A binds more strongly than B. Your advisor asks for your reasoning. Explain which experiment above helped you to make your prediction D. Which proteins are bound to site 1 and 2 in the final experiment 8?

Explanation / Answer

A. Regulatory protein B and C are functioning as the transcriptional activator. This inference can be drawn from experiment no. 3 and 4 when each protein is used individually.

B. Regulatory protein A is a transcriptional repressor. This inference is from experiment no. 2.

C. A binds more strongly than B because in experiment no. 5 when both A and B were added together, the activator effect of protein B was lost. Thus, we can conclude that protein A binds more strongly to site 1 compared to protein B.

D. Protein A is bound to site 1 and protein B is bound to site 2.

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