Final answer:
When an organism utilizes lactose, it also utilizes glucose and galactose as these are the breakdown products of lactose via the action of the enzyme beta-galactosidase encoded by the lac operon in bacteria.
Step-by-step explanation:
If an organism utilizes the sugar lactose, it also utilizes glucose and galactose. This is due to the fact that in organisms such as E. coli, the lac operon encodes the genes necessary for the acquisition and processing of lactose from the environment. Specifically, the Z gene of the lac operon encodes beta-galactosidase, which hydrolyzes lactose into its component monosaccharides: glucose and galactose. These monosaccharides are then utilized in various metabolic pathways within the cell. The lac operon's regulation ensures that these genes are expressed when lactose is present and other more favored carbon sources like glucose are not available.
Metabolism of galactose can lead to its conversion to glycogen or it can be used in the synthesis of lactose in lactating mammary glands. The initial digestion of lactose by the enzyme beta-galactosidase is a critical step for this disaccharide's utilization. Once glucose levels in the cell are low, and lactose is the main carbon source available, the enzymes needed for lactose metabolism, including beta-galactosidase, are produced in response to the activation by the catabolite activator protein (CAP), which is regulated by the levels of cyclic AMP (cAMP).