(i) The secondary structure elements (α-helix & βsheets) further folds to form the three dimensional arrangement. This structure is called tertiary structure of the polypeptide (protein).
(ii) Tertiary structure of proteins are stabilised by the interactions between the side chains of the amino acids.
(iii) These interactions include the disulphide bridges between cysteine residues, electrostatic, hydrophobic, hydrogen bonds and van der Waals interactions.

(i) Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones.
(ii) They are naturally occurring organic substances.
(iii) Carbohydrates are formed in the plants by photosynthesis from water in sunlight.
(iv) They are classified into two types
(a) Sugars Eg: Glucose, Fructose.
(b) Non-sugars Eg: Starch, Cellulose.

Proteins are classified based on their structure (overall shape) into two major types. They are fibrous protein and globular proteins.
(i) Fibrous proteins: These proteins are linear molecules. These are generally insoluble in water and are held together by disulphide bridges and weak intermolecular hydrogen bonds. The Example: Keratin, Collagen etc
(ii) Globular proteins: These proteins have an overall spherical shape. The polypeptide chain is folded into a spherical shape. These proteins are usually soluble in water and have many functions including catalysis.

On hydrolysis, sucrose yields equal amount of glucose and fructose units.
\(Sucrose\overset { Invertase }{ \longrightarrow } Glucose+Frutose\)
Sucrose (+66.6°) and glucose (+52.5^o) are dextrorotatory compounds while fructose is levo rotatory (-92.4°). During hydrolysis of sucrose, the optical rotation of the reaction mixture changes from dextro to levo. Hence, sucrose is called as invert sugar.