Biomolecules - Carbohydrates: Classification and functions

Carbohydrates are defined as optically active polyhydroxy aldehydes or ketones, or compounds which produce such units on hydrolysis. They are also known as saccharides.

Classification based on Hydrolysis: 1. Monosaccharides (cannot be hydrolyzed further, e.g., $C_6H_{12}O_6$). 2. Oligosaccharides (yield 2-10 units, e.g., Sucrose). 3. Polysaccharides (yield a large number of units, e.g., Starch).

Classification based on Reducing Nature: Reducing sugars possess free aldehydic or ketonic groups and reduce Tollen's reagent or Fehling's solution (e.g., Glucose, Maltose). Non-reducing sugars do not (e.g., Sucrose).

Glucose ($C_6H_{12}O_6$) is an aldohexose. Its structure contains one $-CHO$ group, one primary alcoholic group ($-CH_2OH$), and four secondary alcoholic groups ($-CHOH$).

Anomers are a pair of cyclic stereoisomers (diastereomers) of a sugar that differ only in their configuration at the hemiacetal/hemiketal carbon, known as the anomeric carbon (e.g., $\alpha$-D-glucose and $\beta$-D-glucose).

Glycosidic Linkage: The oxide linkage formed between two monosaccharide units through the loss of a water molecule ($H_2O$).

Inversion of Sugar: Sucrose is dextrorotatory ($+66.5^\circ$), but after hydrolysis, it gives a mixture of Glucose ($+52.5^\circ$) and Fructose ($-92.4^\circ$), making the final mixture laevorotatory. This is called 'Invert Sugar'.

Functions: Carbohydrates serve as bio-fuels (Energy source), storage molecules (Starch in plants, Glycogen in animals), and structural material (Cellulose in plant cell walls).