These are molecules of low molecular weight and have higher solubility. These include minerals, water, amino acid, sugars and nucleotides. All molecules or chemicals functional in life activity are called biomolecules.
(1) Elements : On the basis of presence and requirement in plants and animals, they are grouped into major \[(Ca,P,Na,Mg,S,K,N)\] and minor \[(Fe,Cu,Co,Mn,Mo,Zn,I)\] bioelements.
On the basis of function, they may be of following types :–
(i) Framework elements : Carbon, oxygen and hydrogen.
(ii) Protoplasmic elements : Protein, nucleic acid, lipids, chlorophyll, enzymes, etc.
(iii) Balancing elements : Ca, Mg and K.
(2) Biological compounds
(i) Inorganic compounds : Water 80%, inorganic salts 1-3%.
(ii) Organic compounds : Carbohydrates (1.0%), Lipids (3.5%), Proteins (12.0%) Nucleotides (2.0%), Other compounds (0.5).
(3) Cellular pool : Aggregated and interlinked various kinds of biomolecules in a living system. So cell is called cellular pool. It includes over 5000 chemicals. Inorganic chemicals are present mostly in aqueous phase while organic in both, aqueous and non-aqueous. Cellular pool comprises of both crystelloid and colloidal particles. Hence called as crystal colloids.
(4) Water : Liquid of life, major constituent of cell (about 60-90%) and exists in intracellular, intercellular and in vacuoles. In cells it occurs in free state or bound state (KOH, CaOH etc.).
Properties of water : It is colourless, transparent, tastless and odourless, neutral (pH-7) liquid. It is universal solvent, as it can dissolve both polar and non-polar solutes. High boiling point due to hydrogen bonding. Shows high degree of cohesion and adhesion. It can undergo three states of matter i.e., solid\[\rightleftharpoons \]liquid\[\rightleftharpoons \]gas. It is dense and heaviest at 4C and solid below it.
(5) Carbohydrates : e.g., sugars, glycogen (animal starch), plant starch and cellulose.
Source of carbohydrate : Mainly photosynthesis. It exists only in 1% but constitutes 80% of the dry weight of plants.
Composition : It consists of carbon, hydrogen and oxygen in the ratio \[{{C}_{n}}{{H}_{2n}}{{O}_{n}}.\] It is also called saccharide and sugars are their basic components. Classification of carbohydrates are :
(i) Monosaccharides : These are single sugar units which can not be hydrolysed furthur into smaller carbohydrates. General formula is \[{{C}_{n}}{{H}_{2n}}{{O}_{n}},\]e.g., Trioses-3C, (Glyceraldehyde, dihydroxyacetone etc.), tetroses-4C, pentoses-5C, hexoses-6C etc.
Important Hexoses
Glucose : \[{{C}_{6}}{{H}_{12}}{{O}_{6}}.\] Grape sugar is dextrose. Grape is sour due to presence of tartaric acid. Fructose is called fruit sugar (sweetest among natural sugars) and glucose is called "sugar of body" (blood sugar). Normal level of blood glucose is 80-120mg/100ml. If it exceeds then condition is called "glucosuria".
Fructose : Occurs naturally in fruit juices and honey. Hydrolysis of cane sugar in body also yields fructose.
Galactose : It is called as brain sugar. It's an important constituent of glycolipids and glycoproteins.
Properties of monosaccharide
- Monosaccharides are colourless, sweet tasting, solids and show oxidation, esterification and fermentation.
- Due to asymmetric carbon, they exist in different isomeric forms. They can rotate polarized light hence they are dextrorotatory and laevorotatory.
- D-glucose after reduction gives rise to a mixture of polyhydroxy alcohol, sorbitol or mannitol.
more...