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:
Carbohydrates
Lipids
Proteins
Nucleic acids.
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.
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.
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.
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:
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.
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.
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.
Nucleic Acids:
They are the DNA and RNA; they carry genetic information in the cell.
Also help in synthesis of proteins.
Commonly Asked Questions,
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