Question

1. Explain prokaryotic transcription initiation from promoter recognition to transcript elongation. Include the role of the different regions of the sigma factor in formation of the open complex. Explain what strong and weak promoters mean and what determines whether a promoter is strong or weak. Also explain what abortive synthesis is, why it occurs and what has to happen for promoter escape to occur.

2. Explain how the lac operon is turned on/off. What conditions lead to repressor binding, what sequence it binds to (and where that sequence is located) and the consequence of it binding. Know the role of CAP in activation of the lac operon. Know what sequence it binds to (and where that sequence is located and the protein and domain that binds to it. Also know how and why CAP is regulated by cAMP levels. Know what the function of each gene in the operon is.

3. Explain how the trp operon is turned on/off. What are the conditions that lead to repressor binding what sequence it binds to (and where that sequence is located) and the consequence of it binding. Know what attenuation is and the details on how it turns on/off transcription when different levels of trp are present in the cell and how the process of translation plays a role

Answer 1

i explain this questions by pictures pictures.

1)

sigma factor or specificity factor is proteins that need to initate the transcription process. this is facilitating the binding of rna polymerase to gene promoters. they determine the specificity of promoter dna. abortive synthesis is synthesis that explains when rna polymerase binds to promoter and entering to the cycle and there is production of short rna transcript. they are releasing and hereby aborting the whole Process. strong promoter is a promoter that initiate strong transcription process. if concensus sequence dont match the rna polymerase, we can say the promoter is weak.

2)

when glucose level is low camp comes and attaches to the cap site and cap promote the rna polymerase to bind wit the promoter. each genes are coding for certain proteins. beta galactosidase, lactase permease, and permease is produced. they have different functions.

3)

attenuation is the mechanism used in Trp operon to reduce expression. when tryptophan levels are high. by blocking initiation attenuation preventing transcription.