Answer
(a) Arrow A is pointing to the DNA strand.
(b) B is pointing to the regulator gene.
(c) C is pointing to the promoter.
(d) D is pointing to the operator.
(e) E is pointing to the inactive repressor.
Work Step by Step
(a) Arrow A is pointing to the DNA strand.
(b) B is pointing to the regulator gene, which codes for the repressor. The regulator gene usually lies just outside of the operon.
(c) C is pointing to the promoter, which is where RNA polymerase attaches to start transcription.
(d) D is pointing to the operator, which is the site where the repressor binds to prevent transcription. The operator is like an on-off switch, allowing or preventing the genes from being transcribed. Without the repressor bound to the operator, the genes can be transcribed.
(e) E is pointing to the inactive repressor. A repressor is a protein that binds to the operator to prevent transcription of the structural genes. This repressor is inactive because it is not bound to the operator.
