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Biomolecules – Definition, Structure, Classification, Examples

Last Updated : 10 Apr, 2024
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Biomolecules is a chemical compound found in living organisms. They are the building blocks of life, essential for the functioning of living organisms. Biomolecules include protein, carbohydrates, lipids, enzymes, and nucleic acids. They vary in size and structure.

Biomolecules are crucial for life as they help living beings to develop, support, and replicate. In this article, you will find biomolecule notes as we discuss the structure, functions, and types of biomolecules.

What is Biomolecule?

Definition of Biomolecule: They are a chemical compound mainly composed of carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus that are found in living organisms.

Biomolecules are the building blocks of life, and are involved in the maintenance and funcitoning of various life processes. They vary in sizes – from small molecules like primary metabolites to large macromolecules like hormones, proteins, lipids etc.

Small Molecules




Fatty acids




Amino acids

Nucleic acids

Types of Biomolecules

There are four main classes of Biomolecules:

  • Carbohydrates
  • Proteins
  • Nucleic acids
  • Lipids

Types of Biomolecules


Carbohydrates are characterized as polyhydroxy aldehydes or ketones or compounds that produce them on hydrolysis. We recognize carbohydrates as sugars or substances that taste sweet. They are all called saccharides (Greek: saccharin = sugar). Depending upon the quantity of sugar units got upon hydrolysis, they are divided into monosaccharides (1 unit), oligosaccharides (2-10 units), and polysaccharides (in excess of 10 units).

Structurally, carbohydrates consist of carbon, hydrogen, and oxygen atoms. Carbohydrates have numerous uses – they are the most rich dietary source of energy; they are fundamentally vital for the majority of living organic entities as they are present in the structure of various primary part. For example, cellulose is a significant primary fiber for plants.

  • Reducing sugars: They are a type of sugars that can donate electrons to other molecules, often in chemical reactions, due to the presence of a aldehyde or ketone functional group. Hence, acting as reducing agents. All monohybrids and disaccharides (except sucrose) are reducing sugars. They reduce Fehling solution and Tollen’s reagent. Example: Glucose, lactose.
  • Non-Reducing sugars: A type of sugars that do not react with substances like Benedict’s solution. Examples of non reducing sugars is sucrose.

Classification of Carbohydrates

The carbohydrates can be classified on the basis of ther behvaiour in hydrolysis. The substances which yield polyhydroxy aldehydes or ketones on hydrolysis are grouped into:


Monosaccharides are the simplest starches with formula (CH2O)x and are called simple sugars. The most simple monosaccharides contain three to six carbon atoms in an unbranched single chain. Monosaccharides are depicted by the postfix – ose.


Polysaccharides are a class of carbohydrates generated by repeated units of monosaccharides (such as glucose, fructose, and galactose) or disaccharides (such as sucrose and lactose), that are linked together by glycosidic bonds.



Biomolecule proteins are an important group of molecules found in cells. They make up about half of a cell’s dry weight. Proteins are made of smaller units called amino acids, which link together to form long chains called polypeptides. The way these chains fold determines the structure of the protein.

There are different levels of protein structure: primary, secondary, tertiary, and quaternary. Each level depends on how the polypeptide chain folds. Proteins have various functions in cells. For example, myosin is a protein that helps muscles contract, allowing movement. Many enzymes, which are special proteins that speed up chemical reactions, are found in cells. One example is actin, which is found in muscle cells and is important for cell processes.

Also Read: Difference Between Actin and Myosin

Classifications of Proteins

Proteins can be divided into two types.

  • Fibrous Proteins – When protein chains run parallel and held together with hydrogen and disulfide bonds, they form a long, fiber-like structure. These proteins do not dissolve in water. Examples include keratin (found in hair, wool, and silk) and myosin (found in muscles).
  • Globular Proteins- These proteins have a round in shape because their chains twist and fold. They usually dissolve in water. Insulin and albumins are common examples of globular proteins.

Also Read: Difference Between Globular and Fibrous Protein

Protein Structure and Composition

Linderstrom-Lang (1952) specifically first recommended a pecking order of protein structure with four levels: primary, secondary, tertiary, and quaternary.

  • The primary structure of a protein is the specific sequence of amino acids in its chain. This determines the final fold and function of protein. Peptide bonds are formed between amino acids.
  • Secondary structure of protein involves the folding of polypeptide chain due to the formation of hydrogen bonds between amide hydrogen and the carbonyl oxygen of the peptide backbone. This folding can result in formations known as alpha helices or beta sheets, which contribute to the overall shape and stability of the protein.
  • Tertiary structure of protein is a 3D shape formed by folding and twisting of secondary structure. It is stablized by H-bonds, electrostatic forces, disulphide linkages, and Vander Waals forces stabilize.
  • Quaternary structure of protein forms between two or more polypeptide chains.


Nucleic Acids

Nucleic acids are the genetic material found in cells, carrying information from parents to offspring. There are two types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Nucleic acid function involves transferring genetic information and protein synthesis through transcription and translation.

The nucleic acids building block are the nucleotide, made of a nitrogenous base, a sugar, and a phosphate group. These nucleotides link together through a a 3’ and 5’ phosphodiester bond. DNA contains four nitrogenous bases: adenine, guanine, cytosine, and thymine, while RNA replaces thymine with uracil. The structure of DNA is like a twisted ladder, known as a double helix, formed by hydrogen bonds between two anti-parallel chains.


Also Read: Nitrogenous Bases


Lipids biomolecules are organic substances that are insoluble in water but soluble in organic solvents. Lipids are connected with unsaturated fats, and are used by the living cell. Lipids include fats, waxes, sterols, fat-soluble vitamins, mono-, di-or -triglycerides, phospholipids, and so on. Lipids are not polymeric molecules. They are the main source of energy to the cell.



Enzymes can be defined as the biomolecules that catalyzes chemical reactions in our body. Most enzymes are proteins which have catalytic abilities. Enzymes play a crucial role in metabolic processes and different chemical reactions that occur in the cell. The macromolecular components of all enzymes consist of protein except in ribozymes.

These enzymes react with substrates, which bind to enzyme’s active sites, and convert them into different substances called products. In the process catalysts or the enzymes remains unchanged, both in terms of quantity and chemical properties. The binding of substrates to active sites is highly selective.

Enzymes are  divided into six functional classes and are classified according to the type of reaction they catalyze. These are –


Biochemical Property


catalyze oxidation-reduction reactions by transferring electrons between molecules.


catalyze transfer or exchange of functional groups between molecules


catalyze the breakdown of molecules by adding water (i.e hydrolysis)


catalyze the breaking of chemical bonds without using water


catalyze the rearrangement of atoms within molecules to form isomers


join two molecules together by forming new chemical bonds

Also Read: Mechanism of Enzymes Action

Conclusion – Biomolecules

Biomolecules are vital components of living organisms, playing essential roles in various biological processes such as reproduction, growth, and sustenance. Understanding the structure of biomolecules is crucial for understanding how life functions at a molecular level. Carbohydrates, proteins, lipids, nucleic acids, adn enzymes are the types of biomolecules.

Also Read:

FAQs – Biomolecules

What is Biomolecule?

A biomolecule is a chemical compound mainly composed of carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus that are found in living organisms.

Why are Biomolecules Important in Life?

Biomolecules are crucial as they participate in different life processes. They help in organisms to grow, reproduce and sustain themselves.

What is the Most Important Biomolecule?

Nucleic acids are the most important biomolecule as they are involved in storing and transferring genetic material from parents to offsprings.

What are the 4 Main Biomolecules?

The 4 main classes of biomolecules are – carbohydrates, lipids, proteins, and nucleic acids.

What are Proteins?

Proetins are the building blocks of life that are made up of amino acids. These organic molecules are present in all living organisms.

What are Enzymes?

Enzymes are biomolecules that catalyzes chemical reactions in our body. They are high molecular weight proteinous compounds.

What are the Characteristics of a Biomolecules?

Biomolecules are organic molecules essential for life which are characterized by specific structures and functions. They have asymmetrical shape, simple structure, and are important for survival.

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