What are macromolecules? Give examples.

(i) Living matter in plant cells was named ‘protoplasm’ by Purkinje ($1839$) and Hugo von Mohl ($1846$).

(ii) Protoplasm was called the ‘physical basis of life’ by Thomas Huxley in $1868$ .

(iii) Three most important (abundant) elements in protoplasm are carbon, hydrogen and oxygen.

(iv) The relative abundance of carbon, hydrogen and oxygen is higher in living systems when compared to inanimate matter.

(v) The collection of various types of molecules in a cell is termed ‘cellular pool’.

(vi) Small molecules of the cell include sugars, lipids, amino acids, nucleotides, minerals, and water.

(vii) Alkaloids, flavonoids, rubber, essential oils, antibiotics, coloured pigments, scents, gums and spices are called secondary metabolites.

2. Proteins:

(i) Proteins are heteropolymers made of amino acids.

(ii) These are the principal organic constituent of a living cell in order of relative abundance.

(iii) These are the most diverse chemicals in a living organism.

(iv) Protein structure can be of four levels primary, secondary, tertiary and quaternary.

(v) Although about $300$ amino acids occur in nature, only $20$ of them enter into the composition of proteins.

(vi) Glycine is the simplest amino acid, with the lowest molecular weight and no asymmetrical carbon atom.

(vii) Tryptophan is the most complex amino acid which contains an indole ring.

3. Lipids:

(i) Lipids are the biomolecules that are soluble in non-polar solvents.

(ii) These are the polymer of fatty acids and glycerol.

(iii) Fats and oils are glycerides in which fatty acids are esterified to glycerol.

(iv) Essential fatty acids are some polyunsaturated fatty acids which cannot be synthesised in the animal body.

(v) Linoleic, linolenic and arachidonic acids are essential fatty acids.

(vi) Cholesterol is one of the most important animal steroids which is insoluble in water and chemically unreactive.

4. Nucleic Acids:

(i) Nucleic acids like DNA, RNA are the polymer of nucleotide like adenine, guanine, cytosine, uracil and thymine.

(ii) These serve as genetic material.

(iii) These carry hereditary information and are passed on from parental generation to progeny. DNA is a long polymer consisting of a long chain of monomers called deoxyribonucleotides.

(iv) In $1953$, J. D. Watson and F. H. C. Crick proposed the three-dimensional structure of DNA.

5. Polysaccharides:

(i) Polysaccharides are composed of sugars like glucose.

(ii) Cellulose and chitin are two structural polysaccharides.

(iii) The major component in the rigid cell walls in plants is cellulose.

(vi) Chitin is a polysaccharide found in the outer skeleton of arthropods.

(v) Starch and glycogen are the examples of two food storage polysaccharides.

6. Enzymes:

(i) Enzymes are the biocatalyst that increase the rate of a reaction. Almost all the enzymes are proteins.

(ii) These are denatured at high temperatures.

(iii) Holoenzyme is a conjugated protein, consisting of a protein component, apoenzyme and a nonprotein constituent called cofactor.

7. Nature of Bonds Linking Monomers in a Polymer:

(i) In a polypeptide or a protein amino acids are linked by a peptide Bond. 

(ii) Glycosidic bonds help in linking monosaccharides or sugars in polysaccharides.