Question

please help me with the question 15 to 18.

Basic structure of an operon Note that the diagram below is one section of DNA master strend with some areas of DNA labeled in blocks The bracketed area illustrates the basic parts of an operon repressor gene promoter operator structural genes DNA 3 mRNA 5 - 3 repressor protein shown attached to operator #2 Repressor preten "Use purple to color in the repressor gene. The repressor gene codes for a repressor protein. (The repressor gene is also called the regulator gene because it ultimately controls the operon.) 9) What process does arrow #1 represent? arrow #27 "Use red to color in the repressor protein Notice that the repressor protein has the exact shape to allow it to attach to the operator *Use green to color the promoter region of the DNA strand, 10) What enzyme attaches to the promoter region in order to transcribe all three structural genes that follow the operator? (Hint: go back and reread if necessary.) *Use yellow to color in the operator. This is a region of DNA that acts as the "on"/"off" switch for the operon. (Active repressor proteins attach to the operator, but inactive repressor proteins cannot) UUTUITM "Use blue to color in the three structural genes on the diagram. The genes are called structural genes because they code for a protein product (in this case, the protein products are enzymes). 11) If the repressor protein is attached to the operator (and sticking out), can RNA polymerase move past the operator in order to transcribe the structural genes that follow? 12) If the repressor protein is attached to the operator, will the enzymes that the structural genes code for be produced? 13) If the repressor protein is attached to the operator, would the operon be turned "on" or "off"> 14) If the repressor protein is not affached to the operator, con RNA polymerase move past the operator in order to transcribe the structural genes that follow? 15) If the repressor protein is not affached to the operator, will the enzymes that the structural genes code for be produced? 197

Answer 1

Answer 15. a repressor is a protein that attaches to the operator region of an operon and decreases the transcription efficiency by blocking the binding of RNA polymerase enzyme to the promoter region. When a specific inducer is present, it binds to the repressor protein and inhibiting it from binding to operator region. Hence the RNA polymerase enzyme can bind to promoter region and transcription of the structural gene will take place. Thus the enzymes encoded by the structural gene will be produced.

Answer 16. If the repressor protein is not attached to operator region, the operon will be turned on. As stated earlier that repressor protein bind to operator region and negatively regulates operon. Because of the absence of repressor protein at the operator region the site is open for the binding of RNA polymerase enzyme to transcribe the structural genes of the operon.

Answer 17. Yes, the operon allows the gene to be turned on or off. As shown in the figure the structure of operon consist of repressor protein gene, promoter, operator and structural gene. The role of repressor protein is to bind to operator region in operon and block transcription. In some cases for eg. Lac operon, presence of specific inducer will cause the detachment of repressor protein from operator region by binding to it and transcription of structural gene will take place. In some other cases like Trp operon, presence of corepressor will negatively transcribe the operon thus turing the gene expression off.

Answer 18. Most of the eukaryotic genes of metabolic pathway are controlled individually. Each gene specify single enzyme that operates the single step in the metabolic pathway.