The cell of organisms is made up of various organic as well as inorganic elements and water. All the chemicals or molecules essential for the maintenance of all vital or physiological actions of the body are termed biomolecules.

A biomolecule or biological molecules are present in organisms that are essential to one or more biological processes like cell division, morphogenesis, or development.

Most biomolecules are organic compounds. These chemicals are mostly composed of Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur, and phosphorus, these found in living tissues are termed ‘biomolecules’. Biomolecules can be classified as carbohydrates, amino acids, nucleotide bases, fatty acids, etc.

  • Some important inorganic constituents are also found in livings as such: Sodium, potassium, calcium, magnesium, and other compounds like NaCl, CaCO3, etc. These elements help in several functions like major cations (Na, K) and anions(Cl) in most physiological processes as well as involved in energy transfer reactions(P in ATP).
  • The biomolecules include macromolecules, i.e., proteins, nucleic acids, lipids, and polysaccharides in living systems.
  • Biomacromolecules are polymers. which are made up of building blocks of different types. Biomacromolecules have molecular weights ranging from 18 to around 800 daltons (Da) approximately.
Endogenous and exogenous:

Biomolecules are important elements of living organisms. These are endogenous and exogenous.

  • Endogenous biomolecules: These are biomolecules produced within organisms.
  • Exogenous biomolecules: These are usually needed to survive. For example- certain nutrients

Types of Biomolecules

There are various types of biomolecules including:

  • Small molecules:
    • Lipid
    • Fatty acid
    • Glycolipid
    • sterols
    • monosaccharides
    • Vitamins
    • Hormones
    • Metabolites
  • Monomers, Oligomers, and polymers.
    Average cellular composition in organisms
    Component % of the total cellular mass in an organism
    Water 70-90
    Proteins 10-15
    Carbohydrates 3
    Lipids 2
    Nucleic acids 5-7
    Ions 1
     Table- average cellular composition.
    1. Carbohydrate (Saccharides)
    • These are composed of carbon hydrogen and oxygen. Carbohydrates having a ratio of the hydrogen-oxygen atom is 2:1. Carbohydrates are divided into four chemical groups monosaccharide, disaccharide, oligosaccharide, and polysaccharide.
    • The carbohydrates show the general formula Cn(H2O)n or (CH2O)n

    Monosaccharide: Simple sugars

    General formula: CnH2nOn. These have the lower molecular weight and these are the smallest sugars

    Monosaccharides usually have 3-7 atoms per molecule and are named on the basis of C atoms:

    1. Trioses: Contains three carbon atoms per molecule -C3H6O3. Examples- glyceraldehyde, dihydroxyacetone
    2. Tetroses: Posses four carbon atoms and have the empirical formula of C4H8O4, e.g. erythrose
    3. Pentoses: These consist of five Carbon atoms and the empirical formula of C5H10O5, e.g., xylose, ribose, ribulose, etc.
    4. Hexoses: They contain six carbon atoms per molecule with empirical formula C6H12O6, e.g., glucose, fructose, galactose. The different arrangement of atoms gives them different chemical properties.
    5. Heptose: These are seven Carbon monosaccharides with empirical formula C7H14O7, e.g., sedoheptulose, glucoheptose, galactoheptose.


    pentoses, hexoses, and heptoses exist in two forms: Open chain form and ring form.

    The ring form is of two types:

    1. Pyranose: Hexagon with five carbon and one oxygen. It is formed by the reaction of free hydroxyl group of carbon atom 5 and the aldehyde group of carbon atom 1.
    2. Furanose: Pentagon with 4 carbon atoms and one oxygen where the hydroxyl group of carbon atom 5 reacts with the carbonyl group at carbon atom 2.  
    Glycosidic bond:

    A glycosidic bond is a type of covalent bond which joins carbohydrate molecules to another group, that group may or may not be a carbohydrate. On the basis of the position of the hydroxyl (OH) group present on the first carbon, Glycosidic bonds may be of two types: 

    •  α- Glycosidic bond
    • β- Glycosidic bond.

    Disaccharide: When two monosaccharides join together by a covalent bond through glycosidic linkage, called Disaccharide. For example, sucrose, lactose, maltose.

    Polysaccharides: More than 10 molecules of monosaccharide join together by a glycosidic bond to form polysaccharides these are macro-molecules. Examples – are cellulose, glycogen, etc.

    • Reducing Sugar: This type of sugar has an unlinked potential aldehyde group that is present at their first C- atom termed reducing sugar. ex. Galactose.
    • Non- Reducing sugar: The sugars having an aldehyde in group-linked conditions are termed non-reducing sugars. ex. sucrose, trehalose.
    • Benedict’s reagent: the test is conducted for confirmation of the presence of reducing sugar.
    • The most abundant organic substance present in nature occurs in the form of cellulose in the plant cell wall.
    • In both plants and animals, it is used as a source of energy (sugar). Acting as an important storage form in plants is starch and in animals in the form of glycogen.
    • These are Present in nucleic acids as five-carbon sugar (Ribose in RNA, and deoxyribose in DNA).
    • They work as building blocks, amino sugars, and chemically modified sugars e.g., glucosamine, N-acetyl galactosamine, etc
    • Polysaccharides are found as components of the cell wall of plants
    • Chitin: The polysaccharide found in the cell wall of fungi, and also the exoskeleton of arthropods formed of polysaccharides called chitin.
    Examples of Polysaccharides:

    Some important polysaccharides are given below in the table below:

    Polysaccharide Composition Occurrence and function
    Starch The polymer of glucose-containing a straight chain of amylose and a branched chain of amylopectin. plant species in the form of the main storage of carbohydrates. (food storage)
    Glycogen The polymer of glucose.  It is the main storage of carbohydrates in animals.
    Cellulose Polymer of glucose The cell wall  of the plant (the most abundant organic molecule on the earth)
    Pectin it is a polymer of galactose and its derivatives. Plant cell wall
    Callose The polymer of Glucose in plants, sieve tubes of phloem. formed as a respondent to wounds.
    Hemicellulose the polymer of the pentose sugar The plant cell wall functions as a cell-matrix.
    Chitin The polymer of Glucose found as the exoskeleton of arthropods and also of fungi.
    Lignin The polymer of Glucose found in sclenchyma (dead plant cell)
    Murein these are polysaccharides crossed liked with amino acids found in the cell wall of prokaryotic cells.
    Hyaluronic acid The polymer of sugar acids it is a connective tissue matrix, the outer coat of the eggs of mammals.

    2. Protein

    (The term protein coined by Berzelius- 1837, and Mulder- 1838)

    • The basic structure of the protein was given by F. Sanger.
    • Composed of C, H, O, and N. lies in the category of macro-molecules.
    • Proteins are polypeptides formed by linear chains of amino acids linked by peptide bonds.
    • Proteins are heteropolymers made of amino acids. Proteins play a very important role in living organisms as perform many functions eg. some transport nutrients across the cell membrane, some fight infectious organisms, some are hormones, and some work enzymes.
    • The most abundant protein in animals is collagen protein.
    • In the whole biosphere, the most abundant protein is Ribulose bisphosphate Carboxylase-Oxygenase (RuBisCO)
    • Examples of some important hormones- Trypsin –an enzyme, insulin – a hormone,  antibody – which fights infectious agents.
    • On the basis of the complexity of structure, the proteins can have primary secondary, tertiary, and quaternary structures.
    • The name of primary is based on the positional sequence of amino acids.

    The functions of protein:

    proteins are important for structure, they play a vital role in metabolic reactions in the form of enzymes. DNA synthesis is regulated by proteins in the form of enzymes.

    • It helps in the transportation of nutrients across the cell membrane.
    • Some are helpful in the movement of muscles, e.g. myosin and actin.
    • maintains pH balance, and regulation of the volume of body fluids.
    • helps in blood clotting, immunity, and antibodies.
    3. Amino acid
    • In the basic structure of amino acid central carbon atom is attached to an amino group (–NH2) a carboxylic acid group (–COOH), one hydrogen, and one side group (R) as a functional group.
    • The nature of amino acids is based on a number of amino and carboxyl groups, there are acidic (e.g., glutamic acid), basic (lysine), and neutral (valine) amino acids.
    • As there are 20 types of amino acids (e.g., alanine, cysteine, proline, tryptophan, lysine, etc.)
    • tyrosine, phenylalanine, and tryptophan are aromatic amino acids.
    • certain amino acids are essential for our health and they have to be supplied through our diet.
    • Hence, proteins found in our diet are the source of essential amino acids, we can say that plants are the principal source of amino acids for animals as plants can utilize inorganic nitrogen and synthesize amino acids.
    • The ionizable nature of –NH2 and –COOH groups is a particular property of amino acids. That is why we found a change in the structure of amino acids in different PH solutions.
    • There are two types of amino acids i.e essential (taken from diet) and non-essential amino acids.
    structure of Amino acids with functional group

    structure of Amino acids

    4. Nucleic acid
    • Nucleotides are building blocks of nucleic acid. Nucleic acids serve as genetic material.
    • Nucleic acids are macromolecules.
    • 5types of nucleotides are found. Adenosine, guanosine, thymidine, uridine, and cytidine are nucleosides.
    • A nucleotide is made up of three different components –  A heterocyclic compound (named adenine, guanine, uracil, cytosine, and thymine) a monosaccharide, and phosphoric acid or phosphate.
    • Adenylic acid, thymidylic acid, guanylic acid, uridylic acid, and cytidylic acid are nucleotides, and DNA and RNA contain nucleotides only.
    • Nucleic acids serve as genetic material.
    • A nucleic acid is of two types – deoxyribonucleic acid (DNA) containing deoxyribose and ribonucleic acid (RNA) containing ribose.
    • DNA has one oxygen less in its sugar molecule
    • DNA is  found main genetic material for almost all organisms except certain viruses,
    • RNA molecules are involved in information transfer and perform a role in protein synthesis; in some viruses e.g. TMV (Tobacco Mosaic Virus) it is also found as genetic material.
    • They carry hereditary information and transfer it through parental generation to progeny.
    5. lipids
    • These are composed of C, H, O. having oxygen in a very less amount.
    •  Lipids are generally water-insoluble. They are synthesized by fatty acids and glycerol.
    • Simple lipids are called glycerides. They could be found as simple fatty acids. A fatty acid has a carboxyl group which is attached to an R group.
    • The R group could be methyl (–CH3), or ethyl (–C2H5), or a higher number of –CH2 groups (1 carbon to 19 carbons).
    • The lipids having phosphorous and a phosphorylated organic compound are called phospholipids. Phospholipids are found in the cell membrane.
    • Fats are solid at room temperature, some remain liquid at room temperature are called oils.
    • As it has  low oxygen content and a higher number of C-H bonds it stores a higher amount  of energy and releases more energy during its oxidation
    • A molecule of fat can yield twice the energy compared to carbohydrates.
    • Phospholipids are important components of cell membranes
    • An example of simple lipid is glycerol which is trihydroxy propane.
    6. Vitamins
    • Vitamins are organic compounds required in the diet of animals and are very important for their healthy growth.
    • According to the solubility of vitamins, they are divided into two groups- Water-soluble e.g. vitamin B and ascorbic acid, and fat-soluble vitamins (eg. A, D, E, K)
    • Plants synthesize vitamins from CO2, NH3, and H2S.
    • Vitamins (taken from the plant) are essential nutrients as these are not formed directly by animals and their deficiency causes many diseases.   (we will explain vitamins in a separate blog).

    You can also read:

    Thank you 🙂 

    Spread Your Love


    Chemical classification of hormones - Biology PCSSTUDIES % · March 17, 2021 at 2:39 pm

    […] Protein hormones– These are made along a chain of linked amino acids. […]

  • Biological classification-Five Kingdom - Biology PCSSTUDIES · August 11, 2021 at 11:20 pm

    […] W.M. Stanley (1935) showed these viruses could be crystallized and crystals consist of proteins. […]

  • Lipids- Definition, Function, and Categories - PCSSTUDIES - Science · February 8, 2022 at 9:47 pm

    […] lipids are Macro biomolecules, these are diverse groups of compounds including fats, oils, hormones, etc. that are insoluble in […]

  • Nutrition - PCSSTUDIES % Biology · October 18, 2022 at 1:48 pm

    […] seven basic components of nutrients are carbohydrates, protein, fat, vitamins, minerals, fiber, and […]

    Nutrition in organisms - PCSSTUDIES % Biology · October 18, 2022 at 1:53 pm

    […] seven basic components of nutrients are carbohydrates, protein, fat, vitamins, minerals, fiber, and […]

  • Leave a Reply