Lactose is a disaccharide present in milk $($lactis is milk in Latin$).$

$4\mathrm{.}1$ Draw the structure of the two sugar molecules that are the building blocks of lactose

in their closed form.

$4\mathrm{.}2$ Identify the type of glycosidic linkage in lactose.

$4\mathrm{.}3$ Draw curved arrows mechanism for acid$-$catalyzed hydrolysis of lactose.