(a) Hydrolysis products of lactose
$$\underset{\text{lactose}}{C_{12}H_{22}O_{11}} + H_2O \xrightarrow{\text{lactase}} \underset{\text{galactose}}{C_6H_{12}O_6} + \underset{\text{glucose}}{C_6H_{12}O_6}$$
Products : $\beta$-D-galactose and $\beta$-D-glucose
Structure note : the two units are joined by a $\beta$-1,4-glycosidic linkage between C-1 of galactose and C-4 of glucose.
Two further points worth knowing :
Lactose is a reducing sugar, because the glucose unit retains a free anomeric carbon at C-1. A potential aldehyde group therefore remains, and lactose reduces Tollens' and Fehling's reagents.
Lactose is the sugar of milk, which is why it is also called milk sugar. People lacking the enzyme lactase cannot hydrolyse it, which is the cause of lactose intolerance.
(b) Non-essential amino acids
Definition : Amino acids that can be synthesised within the human body and therefore need not be supplied through the diet are called non-essential amino acids.
Key points :
- Ten of the twenty amino acids found in proteins are non-essential.
- The body makes them from other metabolic intermediates as required.
Examples : glycine, alanine, aspartic acid, glutamic acid, serine.
The other ten, which the body cannot make, are the essential amino acids — valine, leucine, isoleucine, lysine, phenylalanine, threonine, tryptophan, methionine, histidine and arginine. A deficiency of these in the diet leads to protein deficiency disorders such as kwashiorkor.
