Class 11 Biology


All the carbon compounds which are obtained from living tissues are called biomolecules.


Biomolecules with molecular eights less than one thousand Dalton are called micromolecules or simply as biomolecules.


Biomolecules with molecular weights more than one thousand Dalton are called biomacromolecules. These are found in the acid-insoluble fraction.

Analysis Of Chemical Composition

For this, a living tissue is taken. The tissue is ground in trichloroacetic acid (Cl3CCOOH), by using pestle and mortar. The slurry is then filtered through a cloth. The filtrate contains acid-soluble pool and the retentate contains acid-insoluble fraction.

Organic compounds are found in the acid-soluble pool, while inorganic substances are found in acid-insoluble fraction.

Amino Acids

Amino acids are organic compounds which contain an amino group and an acidic group as substituents on the same carbon, i.e. α-carbon. Due to this, they are called α-amino acids. The amino acids are substituted methanes. There are four substituent groups which occupy the four valency positions. These groups are; hydrogen, carboxyl group, amino group and a variable group; called R group. The nature of the R-group governs a particular type of amino acids.

However, there are only 21 types of amino acids which occur in proteins. The R-group in these proteinaceous amino acids could be of various types. The amino, carboxyl and the R functional groups decide the chemical and physical properties of an amino acid.

Amino acid with a hydrogen is called glycine, one with a methyl group is called alanine, one with hydroxyl methyl group is called serine, etc. Based on the number of amino and carboxyl group, the amino acids can be acidic, basic or neutral. A particular feature of amino acid is the ionizable nature of –NH2 and –COOH groups. Hence, structure of amino acids changes in solutions of different pH.


Lipids are usually insoluble in water. Lipids can be simple fatty acids and some lipids have phosphorous and phosphorylated organic compounds in them. Lipids; containing phosphorus; are called phospholipids. A fatty acid has a carboxyl group attached to an R group. The R group can be a methyl or ethyl or higher number of CH2 group (1 carbon to 19 carbons).

Fatty acids could be saturated or unsaturated. Many lipids have both glycerol and fatty acids. In this case, the fatty acids are found esterified with glycerol. They can be monoglycerides, diglycerides and triglycerides. On the basis of melting points, they can be termed as fats and oils. Oils have lower melting points while fats have higher melting points.

Nuceloside and Nucleotide

There are a number of carbon compounds with heterocylic rings found in living organisms. Some of them are nitrogenous bases, e.g. adenine, guanine, cytosine, uracil and thymin. When a nitrogenous base is attached to a sugar, it is called a nucleoside, e.g. adenosine, guanosine, thymidine, uridine and cytidine. If a phosphate group is also found esterified to the sugar then they are called nucleotides, e.g. adenylic acid, thymidylic acid, guanylic acid, uridylic acid and cytidylic acid.

Primary Metabolites

Metabolites which have identifiable functions are called primary metabolites. They play known key roles in normal physiological processes. All the primary metbaolites are found in animal cells.

Secondary Metabolites

There are certain metabolites about which we do not have enough information to suggest their role in physiological processes. Such metabolites are called secondary metabolites. Secondary metabolites are not found in animal cells.

Primary MetabolitesSecondary Metabolites
SugarPigments: carotenoids, anthocyanins
Amino acidsAlkaloids: morphine, codeine
FatsTerpenoids: monoterpenes, diterpenes
Nitrogen basesEssential oils
NucleotidesToxins: abrin, ricin
NucleosidesLectins: concalavalin A
Drugs: vinblastin, curcumin
Polymer substances: rubber, gum, cellulose