Repressor molecules bind to
a) Operator
b) Promoter
c) Enhancer
d) Hormone response element
An operon has certain regulatory sequences that help in the regulation of transcription. They can either promote or inhibit the transcription based on the need for particular gene expression. Operon acts as a single regulated unit having one or more structural genes, a promoter gene, a regulator gene. A repressor and an inducer.
(a) Operator – it controls the synthesis of mRNA over the structural genes. The presence of the repressor switched off its expression. To switch on the operator gene, the inducer binds with the repressor and takes it away. Once it switches on, it directs the structural gene to perform transcription. Thus it is the correct answer.
(b) Promoter – it functions as a recognition site of RNA polymerase provided that the operator is switched on. When the operator is functional, RNA polymerase moves over it and reaches the structural genes. Thus it is an incorrect answer.
(c) Enhancer - Promoter has different parts to which the transcription factors attach to initiate the process of transcription. Besides promoter certain other control elements are present upstream of the transcription unit known as enhancers. The enhancers can be thousands of base pairs upstream of the transcription unit and influence the transcription process by acting as control groups. Thus, it is an incorrect answer.
(d) hormone response elements – the hormone response elements are present within the promoter region of a gene and are small DNA sequences. These play an important role in regulating the process of transcription by binding to a specific hormone-receptor complex. Thus, it is an incorrect answer.
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