Answer:
If we add glucose to the culture with lactose, the <em>lac operon</em> would be turned off and the production of <em>beta-galactosidase, </em>other enzymes and molecules that the operon transcribes, would decrease.
On the contrary, if we add lactose to a bacterial culture containing glucose, the <em>lac operon</em> would be on, transcribing the genes, hence, producing beta-galactosidase but only at a small rate. Because the bacteria already got the energy from the glucose.
Explanation:
An operon is a group of structural genes whose expression is regulated by a <em>promoter, operator and regulator genes</em>. In this particular case, they are talking about the lactose operon, <em>lac operon</em>. This operon is required, in bacteria, to obtain energy from lactose when there is no glucose present.
The lac operon contains a series of genes, <em>lacZ, lacY</em>, and <em>lacA</em>. The gene <em>LacZ</em> codifies an enzyme required to break the lactose, <u>beta-galactosidase</u>. <em>LacY</em> codifies for another enzyme required in the transport of lactose inward the cell. And finally, <em>LacA</em> produces a molecule that is involved in detoxification.
The <em>lac operon</em> is regulated, among others, by the presence of glucose and lactose. The glucose is the preferable source of energy for bacteria so if there are lactose and glucose the glucose would be used for energy at a bigger extent. In the <u>absence of glucose</u>, the <em>lac operon</em> plays a vital role and helps the bacteria to obtain energy from lactose.
When there is glucose but no lactose available, there is a <u>repressor</u> than binds to the promoter so the <em>lac operon</em> is OFF cannot express the genes.
On the other hand,when there is lactose and no glucose, lactose enters the cell and some of this molecules turn to alolactose. <u>Alolactose molecules</u> bind to the repressor so the operon is not repressed anymore and the <em>lac operon</em> would be ON producing enzimes and molecules.
If the <em>lac operon</em> is ON ( glucose absent ) the production of <u>beta-galactosidase</u> would be high, on the other hand, if the operon is OFF (glucose present) the production of <u>beta-galactosidase</u> decreases.
In the presence of <u>both lactose and glucose</u>, the genes for the lactose metabolisms are transcribed at low rates in the <em>lac operon</em>.
