Question

Which of the following would you expect to find in an inducible system:
(A) A repressor protein, which is bound to DNA in absence of any other factor.
(B) A repressor protein, which is bound to DNA in the presence of a co-repressor.
(C) An activator protein, which is bound to DNA in absence of any other factor.
(D) An activator protein, which is bound to DNA only in the absence of an inhibitor.

Answer 1

Hint: An inducible operon is usually turned off and it needs an inducer to turn it on. It has a repressor protein which is bound to DNA in the presence of a co-repressor.

Step by step solution:
A quantifiable increase in expression in response to an enhancer, inducer, or positive regulator is known as an inducible operon. The primary distinction between inducible and repressible operons is that the former is turned off under typical circumstances, whilst the latter is turned on. Usually turned off, an inducible operon participates in the degradation of a nutrient (catabolic pathways). Inducible operons include lac operons. When an inducer controls an operon, the operon is said to be inducible. An inducible operon is what it is termed. The operon can be turned on or off by an inducer. An illustration of an inducible operon is the lac operon. Beta-galactosidase uses lactose as a substrate, and lactose also activates the lac operon. An inducible operon that encodes enzymes for the metabolism of the sugar lactose is the lac operon. Only when the sugar lactose is present does it turn on (and other, preferred sugars are absent). Allolactose, a modified version of lactose, is the inducer in this situation.
Genes involved in lactose metabolism are found in the lac operon of E. coli. It only expresses itself when lactose and glucose are both absent. The lac repressor and catabolite activator protein are two regulators that control the operon's "on" and "off" states in response to lactose and glucose concentrations (CAP).
So, option (B) is correct.
Note: Regulator genes, promoter genes, operator genes, and structural genes are some of the parts of the lac operon. Repressor, a substance produced by regulatory genes, combines with the operator gene to turn off the operon.