Question

In the presence of lactase, lactose breaks down into molecules of
A. Glucose and galactose
B. Glucose and fructose
C. Galactose only
D. Glucose only

Answer 1

Enzymes are proteins that act as catalysts that accelerate chemical reactions. Enzymes increase the rate of reaction by decreasing the activation energy of substrates. Lactose is a disaccharide and has a molecular formula ${C_{12}}{H_{22}}{O_{11}}$. Lactase is an enzyme that is produced by many organisms. Lactase is required for the complete digestion of milk in the small intestine.

Complete step by step answer: Lactase enzyme is a part of the β-galactosidase family.
Lactase found along the brush border membrane of villi in the small intestine.
The optimum temperature and pH for lactase in humans is 37 ° C and 6 pH.
Lactase is encoded by a single genetic locus found on chromosome 2.
Lactose is formed by subunits of glucose and galactose.
In the process of metabolism, the β-glycosidic bond of disaccharide D-lactose is hydrolyzed by lactase and two monosaccharides D-galactose and D-glucose are obtained as a product.
When lactase attacks on D-lactose then D-glucose is obtained and an intermediate known as α-galactosyl is formed.
After the completion of hydrolysis, D-galactose was obtained by the breaking of α-galactosyl.
The following reaction is taking place here:
$$$$$${C_{12}}{H_{22}}{O_{11}}\left( {Lactose} \right) + {H_2}O;; \to ;{C_6}{H_{12}}{O_6}\left( {Glucose} \right) + {C_6}{H_{12}}{O_6}\left( {Galactose} \right) + HEAT$$.
According to this in the presence of lactase, lactose will break down in glucose and galactose.
So, the correct option (A) is correct.

Note: Decreased ability to digest lactose due to lack of lactase is known as lactose intolerance. The common symptoms of lactose intolerance are diarrhea, gas, bloating, and abdominal pain. In lactose intolerance changing diet to avoid food and milk products that contain lactose is beneficial or they can use lactase enzyme tablets or drops which will help them to digest lactose.