Question

"Housekeeping genes" in bacteria are commonly expressed constitutively, but not all

of these genes are expressed at the same level (the same number of molecules per
cell). The primary mechanism responsible for variations in the level of constitutive
enzymes from different genes is that:
A) all constitutive enzymes are synthesized at the same rate, but are not
degraded equally.
B) their promoters have different affinities for RNA polymerase holoenzyme.
C) some constitutively expressed genes are more inducible than others.
D) some constitutively expressed genes are more repressible than others.
E) the same number of mRNA copies are made from each gene, but are
translated at different rates.

Answer 1

B) their promoters have different affinities for RNA polymerase holoenzyme.

Step-by-step explanation:

The housekeeping genes are the one whose products are involved in the vital metabolic pathways. So, these genes are mostly expressed at a constant level in the cells. However, the protein products of housekeeping genes exhibit variations in their cellular concentration.

The variation in the expression of housekeeping genes is regulated by the interaction between RNA polymerase holoenzyme and promoter.

The variations in the promoter sequences of these genes regulate the rate of the initiation of transcription by affecting the interaction between RNA polymerase-promoters. Certain promoter sequences facilitate the binding of RNA polymerase more than the other ones. This differential interaction regulates the rate of transcription initiation and accounts for variable cellular concentration of products of housekeeping genes.