• Definition:

    • Biomolecules are molecules that occur naturally in living organisms.

  • Biomolecules include macromolecules like proteins, carbohydrates, lipids and nucleic acids

  • It also includes small molecules like primary and secondary metabolites and natural products. 

  • Biomolecules consist mainly of carbon and hydrogen with nitrogen, oxygen, sulfur, and phosphorus. 

  • Biomolecules are very large molecules of many atoms, which are covalently bound together.

Classification of Biomolecules:

  • There are four major classes of biomolecules: 

  1. Carbohydrates

  1. Lipids

  2. Proteins

  3. Nucleic acids.

  1. Carbohydrates - 

  • Carbohydrates are a good source of energy. 

  • Carbohydrates (polysaccharides) are long chains of sugars.

  • Monosaccharides are simple sugars that are composed of 3-7 carbon atoms. - They have a free aldehyde or ketone group, which acts as reducing agents and hence are known as reducing sugars

  • Disaccharides are made of two monosaccharides. 

  • The bonds shared between two monosaccharides are the glycosidic bonds

  • Monosaccharides and disaccharides are sweet, crystalline and water soluble substances. 

  • Polysaccharides are polymers of monosaccharides

  • Polysaccharides are un-sweet and complex carbohydrates

  • Insoluble in water and are not in crystalline form.

  • Example: glucose, fructose, sucrose, maltose, starch, cellulose etc.

  1. Lipids -

  •  Lipids are composed of long hydrocarbon chains

  • Lipid molecules hold a large amount of energy and are energy storage molecules

  • Lipids are generally esters of fatty acids and are building blocks of biological membranes. 

  • Most of the lipids have a polar head and nonpolar tail

  • Fatty acids can be unsaturated and saturated fatty acids. 

  • Lipids present in biological membranes are of three classes based on the type of hydrophilic head present:  

    • Glycolipids are lipids whose head contains oligosaccharides with 1-15 saccharide residues.  

    • Phospholipids contain a positively charged head which are linked to the negatively charged phosphate groups.  

    • Sterols, whose head contains a steroid ring. Example steroids.

  • Example of lipids: oils, fats, phospholipids, glycolipids, etc.

  1. Nucleic Acids:

  • Nucleic acids are organic compounds with heterocyclic rings. 

  • Nucleic acids are made of polymers of nucleotides

  • Nucleotides consist of a nitrogenous base, a pentose sugar and a phosphate group. 

  • A nucleoside is made of a nitrogenous base attached to a pentose sugar

  • The nitrogenous bases are adenine, guanine, thiamine, cytosine and uracil

  • Polymerized nucleotides form DNA and RNA which are genetic material. 

  1. Proteins:

  • Proteins are heteropolymers of amino acids

  • Amino acids are joined together by the peptide bond which is formed in between the carboxyl group and amino group of successive amino acids. 

  • Proteins are formed from 20 different amino acids, depending on the number of amino acids and the sequence of amino acids.

  • There are four levels of protein structure: 

    • Primary structure of Proteins:

      • Here protein exists as a long chain of amino acids arranged in a particular sequence. 

      • They are non-functional proteins. 

    • Secondary structure of proteins:

      • The long chain of proteins are folded and arranged in a helix shape, where the amino acids interact by the formation of hydrogen bonds

      • This structure is called the pleated sheet. 

      • Example: silk fibers. 

    • Tertiary structure of proteins:

      • Long polypeptide chains become more stabilized by folding and coiling, by the formation of ionic or hydrophobic bonds or disulphide bridges, these results in the tertiary structure of protein. 

    • Quaternary structure of proteins:

      • When a protein is an assembly of more than one polypeptide or subunits of its own, this is said to be the quaternary structure of protein. 

      • Example: Hemoglobin, insulin.

Biological Importance of Biomolecules:

  1. Carbohydrates: 

  • They provide the body with a source of fuel and energy, it aids in proper functioning of our organs. 

  • Deficiency of carbohydrates in the diet causes fatigue and poor mental function.

  1. Proteins:

  • Each protein in the body has specific functions, some proteins provide structural support, help in body movement, and also defense against infections. 

  • Proteins can be antibodies, hormonal, enzymes and contractile proteins

  1. Lipids:

  • The primary purpose of lipids in the body are energy storage

  • All biological membranes are lipoidal in nature.

  • Lipid hormones, like sterols, help in mediating communication between cells. 

  1. Nucleic Acids:

  • They are the DNA and RNA; they carry genetic information in the cell

  • Also help in synthesis of proteins.

Commonly Asked Questions,

  1. Write a short not on “Biomolecules”.

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