Question

Which of these is/are hexose sugar/s
(A) Arabinose
(B) Galactose
(C) Mannose
(D) Both B and C

Answer 1

Arabinose, galactose and mannose, all are the difference of monosaccharides. The monosaccharide is the basic unit of any carbohydrate. Both galactose and mannose are hexose sugars as they have six carbons in their molecular structures, whereas arabinose is a pentose sugar.

Complete answer:
- The major constituents of monosaccharide units are carbon (C), hydrogen (H) and oxygen (O) moieties. The monosaccharide could be represented with a general formula: ${C_n}{H_{2n}}{O_n}$ , where ‘n’ defines the type of monosaccharide. The monosaccharides are the simplest form of sugars.
- Based on the number of carbon atoms, the monosaccharides are named as pentose (C=5), hexose (C=6) etc. Galactose is a $C - 4$ epimer of glucose $({C_6}{H_{12}}{O_6})$ molecule, whereas mannose is a $C - 2$ epimer of glucose $({C_6}{H_{12}}{O_6})$molecule.
- The arabinose is a type of monosaccharide unit which has five-carbons in its parent structure and thus is considered as pentose sugar. It is abundantly found in natural sources and serves as a distinct source of carbon in numerous bacteria.
- Galactose is mostly used in the development of biologically-active glycol-conjugates in the living organisms. Lactose, a disaccharide moiety found in milk, is formed when one of galactose is conjugated with one glucose molecule.

Note: Arabinose (a pentose sugar) is generally degraded in the presence of proteins which are isolated from three specific genes named as araA, araB, and araD. The degradation of arabinose molecule takes place in the bacterial species belonging to Enterobacteriaceae family. Some of the bacterial species representing this family are Escherichia coli (E. coli) and Salmonella typhimurium (S. typhimurium). Further, the araA, araB, and araD forms a complex structure which is recognized as araBAD.