Which of the following examples of positive/negative regulation is incorrect? A.
ID: 171136 • Letter: W
Question
Which of the following examples of positive/negative regulation is incorrect? A. Negative regulation: A protein is bound to DNA, inhibiting transcription, unless an effector molecule binds to it. B. Negative regulation: A protein binds to DNA, inhibiting transcription, only if an effector molecule binds to it. C. Positive regulation: An effector molecule causes dissociation of a protein from DNA, inhibiting transcription. D. Positive regulation: An effector molecule causes association of a protein to DNA, inhibiting transcription. E. Positive regulation: An effector molecule causes association of a protein to DNA, inducing transcription.Explanation / Answer
In order to answer this question you must understand what a reglator molecule is and what is its function.
A regulator is a protein molecule which is produced by a gene. Now this molcecule binds to the operator site which which might either make the transcription happen or inhibit it, depending on the type of regulator.
A classic mode of control in bacteria is negative control, where a repressor protein prevents a gene from being expressed. When the repressor protein binds to the operator, RNA polymerase is prevented from initiating transcription as it is unable to fbond to the promoter(this is because promoter and operator region are overlapping), and gene expression is therefore turned off.
An alternative mode of control is positive control. In this case special protein actually assist in begining of a process(transcription). The example for this is the initiation of transcription in eukaryotes where transcription factors help RNA polymerase to initiate transcription.
Now let us have a look at the option :
The incorrect options are B,C and D. In option B we must understand that an effector molecule is not necessary to have negative control of a gene. In option C and D we must understand that the positive regulation actually causes the induction of transcription and not inhibition.
Thus the correct options are A and E.
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