Lac Operon In E. coli, three closely linked loci have been identified. The loci
ID: 62714 • Letter: L
Question
Lac Operon
In E. coli, three closely linked loci have been identified. The loci are symbolized by d, m, and s. Wild type alleles are superscripted with a plus, while mutant alleles are superscripted with a minus. When an inducer is present or absent, the level of Enzyme A is measured and the results for several different strains are given below.
Structural gene = __________
Regulator =___________
Operator=___________
For structural gene I'm guessing m+ because m+ is always present when there is a lot of enzyme in the absence of inducer. For regulator I'm guessing m- because there is no enzyme produced when m- is present even in the presence of the inducer. But I'm not really sure if any of that is right. Please help and explain! :)
Explanation / Answer
To understand the above problem, lets first understand the definition of Structural, Regulator and Operator gene.
Structural gene- These genes produce mRNAs (transcription), which in turn synthesize specific polypeptides on the ribosomes (translation). The polypeptides so formed act as enzymes to catalyse some metabolic reaction in the cell.
Regulator Gene- This gene controls the operator gene in cooperation with a chemical substance called inducer present in the cytoplasm. A regulator gene is not necessarily adjacent to the operator gene which it controls.The regulator gene codes for and produces a protein called repressor. The repressor protein binds with the operator gene to repress (stop) its action.
Operator Gene- The operator gene controls the functioning of a specific series of structural genes. It lies adjacent to the structural genes which it controls. The cistrons are expressed when the operator gene is turned on by an inducer, and are not expressed when the operator gene is turned off by a repressor.
M+ will be structural gene as absence of it will not be producing anything , irrespective of presence or absence of Inducer.
d will be regulator gene as presence or absence of Inducer is high in the case where d is mutant.
S will be bydefault operator gene.
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