Read the passage carefully and answer the questions.
Carbohydrates are naturally formed organic compounds from various plants. The common chemical formula, \( (C_x(H_2O)_y) \) was considered as hydrates of carbon to derive the various carbohydrates. For instance, the general formula for glucose \( (C_6H_{12}O_6) \) easily fits into the above formula. Carbohydrates also called saccharides are classified on the basis of their behavior towards hydrolysis. Monosaccharides cannot be hydrolyzed further to simpler units of polyhydroxy aldehyde or ketones. About 20 monosaccharides are known to occur in nature. Carbohydrates that yield large number of monosaccharide units are called polysacccharides. Amino acids contain \( (-NH_2) \) and \( (-COOH) \), which can be classified in various forms. Proteins are polymers of alpha amino acids which are connected to each other by a peptide bond or peptide linkage. When a native protein is subjected to physical change, its globules unfold and helix get uncoiled and the protein loses its biological activity. The protein is said to be denaturated.
The two monosaccharides units are joined together through which linkage?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Glycosidic linkage
In a disaccharide or polysaccharide, two monosaccharide units are joined through an oxygen atom. The bond forms at the anomeric carbon (C1 of an aldose, C2 of a ketose) of one unit, with loss of water:
\( \displaystyle \ce{C6H12O6 + C6H12O6 -> C12H22O11 + H2O} \)
For example, in sucrose the linkage is between C1 of α-D-glucose and C2 of β-D-fructose; in maltose between C1 of one α-D-glucose unit and C4 of the next; in lactose between C1 of β-D-galactose and C4 of glucose.
Why the other options are incorrect
Option (1) Alpha linkage — Incorrect. “Alpha” only describes the configuration at the anomeric carbon that forms the glycosidic bond, as in maltose and starch (α-glycosidic linkages). It is a kind of glycosidic linkage, not a separate type of bond.
Option (3) Beta linkage — Incorrect. In the same way, “beta” describes a β-glycosidic linkage, as in cellulose and lactose. The bond itself is still a glycosidic linkage.
Option (4) Gamma linkage — Incorrect. There is no such linkage in carbohydrates.
NCERT (2026-27 edition):
Disaccharides
