1. The prokaryotic gene regulation is mediated by the operon system in which different genes are regulated within a single mechanism as they produce polycistronic mRNA.
The repressible operon is usually remains on (active). They are usually involved in anabolic pathways. When the end product of this pathway becomes accumulated within the medium then it act as a co-repressor that binds with the inactive repressor molecule and activate the repressor molecule.
Then the activated repressor molecule binds with the operator region of the operon and inactivate it's transcription process. So, the operon becomes inactivated or off.
Tryptophan operon is an example of repressible operon in prokaryotes. The tryptophan (Trp) act as a co-repressor molecule.
1. The enzymes that are produced by the repressible operon are usually involved in anabolic pathway. So, this option is correct.
2. When co-repressor is present then only this operon will be shutdown otherwise the repressible operon is usually remains on in absence of the co-repressor molecule. So, this option is also correct.
3. In repressible operon the repressor molecule is synthesized as an inactive form. When co-repressor is present then the co-repressor binds with the inactive repressor molecule and activates the repressor molecule. So, this option is incorrect.
Hence, option 1 option 2 are correct.