# Biomolecule: Definition, Types, Structure, Functions & Examples

> Biomolecule explained: definition, four major types, chemical composition, functions, examples, and the distinction from biological macromolecules.

Canonical URL: https://biologynotesonline.com/biomolecule/
Author: Sourav Pan
Last updated: October 1, 2026

![Biomolecule: Definition, Types, Structure, Functions & Examples](https://biologynotesonline.com/wp-content/uploads/2024/10/Biomolecule-Definition-Types-Structure-Examples-Significance.jpg)

Biomolecule is a molecule found in living system and it is associated with biological processes. It is also called biological molecule. In the cell, biomolecules are used for cellular structure, metabolism, storage and transfer of genetic information, signaling, and other different biological functions. The four major classes commonly taught are carbohydrates, lipids, proteins, and nucleic acids.

Biomolecules are not all same. They differ in size and also in chemical structure. Some biomolecules are very large molecules, while some are small biologically important molecules. Many biological macromolecules are made when small units, called monomers, join together and form a polymer. But every biomolecule is not a polymer.

Lipids are placed under the major classes of biomolecules. However, lipids are not true polymers like proteins and nucleic acids.

The structure of a biomolecule determines its biological work. Carbohydrate may store or provide energy. Lipid may form membrane structure. Protein may act as enzyme or structural material, and nucleic acid stores hereditary information. So, chemically different molecules are grouped as biomolecules because they take part in the normal structure and functioning of living cells.

## Major Types and Classification of Biomolecules

The classification of biomolecules is mainly based on their chemical structure, type of building unit, linkage pattern, and the function performed in living cells. 

On this basis, the four major classes of biomolecules commonly taught are carbohydrates, lipids, proteins, and nucleic acids. These are not four single molecules. They are four broad groups, and each group contains many different molecules.

![The four major biomolecule classes differ in chemical organization: carbohydrates contain sugar units, proteins are amino-acid polymers, nucleic acids are nucleotide polymers, and lipids comprise structurally diverse hydrophobic or amphipathic molecules.](https://biologynotesonline.com/wp-content/uploads/2024/10/Four-Major-Classes-of-Biomolecules-1024x683.webp)The four major biomolecule classes differ in chemical organization: carbohydrates contain sugar units, proteins are amino-acid polymers, nucleic acids are nucleotide polymers, and lipids comprise structurally diverse hydrophobic or amphipathic molecules.

- Carbohydrates- These are biomolecules made up of sugar units. The simple unit is generally a monosaccharide, such as glucose. Many monosaccharides may join to form larger [carbohydrate molecules](https://biologynotesonline.com/carbohydrates/) like starch, glycogen, and cellulose. Carbohydrates are mostly used for energy supply, energy storage, and also structural support in some cells.

- Lipids- [Lipids](https://biologynotesonline.com/lipids/) are a group of hydrophobic or water-insoluble biomolecules. They are commonly formed from fatty acids and glycerol, but all lipids do not have the same building pattern. They are not true polymers like proteins and nucleic acids. Fats, oils, phospholipids, and steroids are some examples. Lipids are used in energy storage, membrane formation, insulation, and signaling.

- [Proteins](https://biologynotesonline.com/proteins/)- Proteins are biological macromolecules made up of amino acid monomers. Amino acids are joined by peptide bonds and form a polypeptide chain. The chain then folds into a particular shape. This shape gives the protein its specific work. Enzymes, antibodies, transport proteins, and structural proteins are included in this group.

- Nucleic acids- Nucleic acids are polymers of nucleotide monomers. Each nucleotide has a sugar, phosphate group, and nitrogenous base. [Deoxyribonucleic acid (DNA) ](https://biologynotesonline.com/dna-definition-structure-properties-types-functions/)and[ ribonucleic acid (RNA)](https://biologynotesonline.com/rna-definition-structure-types-application/) are the two main examples. DNA stores genetic information, whereas RNA helps in expression of genetic information and protein synthesis.

Biomolecule classTypical building blocksDefining structural featureRepresentative examplesPrincipal rolesCarbohydratesMonosaccharidesSugar units joined into small or large carbohydrate moleculesGlucose, starch, glycogen, celluloseEnergy source, storage, structural supportLipidsFatty acids and glycerol in many formsHydrophobic molecules, not true polymersFats, oils, phospholipids, steroidsEnergy storage, cell membrane, insulation, signalingProteinsAmino acidsPolypeptide chain folded into specific shapeEnzymes, antibodies, collagen, hemoglobinCatalysis, transport, defense, structureNucleic acidsNucleotidesSugar-phosphate backbone with nitrogenous basesDNA, RNAGenetic information storage and expression

This four-type classification is a teaching classification of major biomolecule groups. Smaller biologically important molecules, such as vitamins, hormones, metabolites, and some coenzymes, can also be called biomolecules when they take part in biological function.

### Biomolecules Beyond the Four Major Classes

The four major classes of biomolecules are carbohydrates, lipids, proteins, and nucleic acids. These are the major groups commonly taught in biology. But biomolecule does not mean only these four groups. Many small molecules are also biomolecules, because they are formed in living system or take part in normal biological reactions.

Some biomolecules are large macromolecules. Some are not. They may not be made by repeated monomers, and they may not form a true polymer. Still they are important inside cell, because metabolism, enzyme action, signaling, and regulation depends on many small biologically active molecules.

- Metabolites- These are small molecules formed or used during metabolism. Glucose, pyruvate, amino acids, fatty acids, and many intermediate compounds are included here. Some metabolites enter energy pathways. Some are used for making larger cell molecules.

- Vitamins- [Vitamins](https://biologynotesonline.com/vitamins/) are small organic biomolecules required in very small amount. Many of them work as part of coenzymes. They help enzyme reactions, but they are not proteins themselves.

- [Hormones](https://biologynotesonline.com/hormones-structure-types-functions-examples/)- Hormones are chemical signaling biomolecules. Some are peptide in nature. Some are steroids, and some are derived from amino acids. They carry message from one tissue to another and regulate body functions.

- Coenzymes and cofactors- These are helper molecules required by many enzymes. Nicotinamide adenine dinucleotide (NAD⁺), flavin adenine dinucleotide (FAD), and coenzyme A (CoA) are examples. They help in transfer of electrons, chemical groups, or energy-rich groups during metabolism.

- Secondary metabolites- These biomolecules are produced by plants, microbes, and other organisms. Alkaloids, pigments, antibiotics, toxins, and plant phenolic compounds are included in this group. They may help in defence, attraction, competition, or communication.

## Molecular Structure and Chemical Composition of Biomolecules

![Carbon skeletons and functional groups developing into carbohydrate, protein, nucleic-acid, and lipid structures with their characteristic bonds.](https://biologynotesonline.com/wp-content/uploads/2024/10/Biomolecule-Structure-and-Molecular-Organization-1024x768.webp)Carbon skeletons and functional groups developing into carbohydrate, protein, nucleic-acid, and lipid structures with their characteristic bonds.

Biomolecules are mostly carbon based molecules. Carbon forms the main skeleton, because it can join with another carbon atom and also with hydrogen, oxygen, nitrogen, phosphorus and sulfur. Due to this property, chain, branched, ring and large complex molecules are formed in living cells.

The common elements of biomolecules are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). But this is not complete for all biomolecules. Phosphorus (P) is present in nucleotides and phospholipids. Sulfur (S) is present in some amino acids and proteins. So, CHON should not be written as universal complete composition of every biomolecule.

The structure of biomolecule is based on arrangement of atoms, type of bond, functional groups, molecular size and its three-dimensional shape. A same element set may give different molecule when bonding pattern is changed. This changes its property also. In cell, the shape and chemical groups decide how the molecule will bind, react, fold or remain stable.

- Carbon skeleton- It is the basic framework of many biomolecules. Carbon atoms may be arranged as straight chain, branched chain, or ring. In carbohydrates, this skeleton carries many hydroxyl groups. In many lipids, long hydrocarbon chain is present.

- Functional groups
Functional groups are small atom groups attached to the carbon skeleton. They give chemical property to the molecule. Hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), amino (-NH₂), phosphate (-PO₄) and sulfhydryl (-SH) groups are some important groups. They affect solubility, charge, acidity and reaction nature.

- Molecular size- Biomolecules are not all of same size. Some are small molecules such as glucose, amino acids, fatty acids and nucleotides. Some are large macromolecules, such as polysaccharides, proteins and nucleic acids. Lipids are also important biomolecules, but many lipids are not true polymers.

- Bonding pattern- Covalent bonds make the main structure of biomolecules. Other interactions are also present. Hydrogen bonds, ionic interactions, hydrophobic interactions and disulfide bonds help in folding and stability. In proteins, these interactions are very important for keeping the shape.

- Three-dimensional structure
The three-dimensional form decides many biological functions. Protein shape controls enzyme activity, binding and transport. Nucleic acid structure helps in storage and transfer of genetic information. A small structural change may change the work of molecule.

- Carbohydrates- Carbohydrates are mainly made up of carbon, hydrogen and oxygen. Their basic units are monosaccharides. These units join by glycosidic bonds to form disaccharides and polysaccharides. Glucose, starch, glycogen and cellulose are examples.

- Lipids- Lipids are rich in carbon and hydrogen. In many cases, they contain less oxygen than carbohydrates. They are hydrophobic in nature. Fatty acids, glycerol, phospholipids, oils, fats, waxes and steroids are included here. Phospholipids contain phosphorus and they form important part of cell membrane.

- Proteins- Proteins are made up of [amino acids](https://biologynotesonline.com/amino-acids/). Amino acids contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Amino acids are joined by peptide bonds and form polypeptide chain. The chain folds into a specific structure, and this structure gives the [protein](https://biologynotesonline.com/proteins/) its particular function.

- Nucleic acids- Nucleic acids are polymers of nucleotides. Each nucleotide has sugar, phosphate group and nitrogenous base. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) contain carbon, hydrogen, oxygen, nitrogen and phosphorus. The sugar-phosphate backbone and sequence of bases are the main structural features.

## Formation and Breakdown of Larger Biomolecules

### Formation of Larger Biomolecules

Larger biomolecules are formed by joining of small biological units. These small units are called monomers. When many monomers join one after another, a polymer is formed. It is not a random joining process. Enzymes control these reactions inside the cell.

A monomer is a small molecule unit. A polymer is a large molecule formed from many monomers. Proteins, polysaccharides, and nucleic acids are true polymers.

Condensation reaction- In this process, two small molecules join together and form a covalent bond. One molecule of water is removed during the bond formation. This is also called dehydration synthesis.The reaction is as follows- Monomer + Monomer → Dimer + H₂O

- Carbohydrate formation- In carbohydrates, monosaccharides are joined by glycosidic bonds. Many glucose units may join and form starch, glycogen, or cellulose. Water molecule is removed during bond formation.

- Protein formation- Proteins are formed from amino acids. The amino group of one amino acid joins with the carboxyl group of another amino acid. A peptide bond is formed. Water is removed here also. Many amino acids form a polypeptide chain, and later it folds to form protein structure.

- Nucleic acid formation- Nucleic acids are formed from nucleotides. The nucleotides are joined by phosphodiester bonds. This forms the sugar-phosphate backbone. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are formed from nucleotide units.

- Lipid formation- Lipids are not formed like true polymers. In fats, fatty acids are joined with glycerol by ester bonds. Water is removed during this ester bond formation. So, lipids are large biomolecules in many cases, but they are not true polymer like protein or nucleic acid.

- Energy requirement- Many formation reactions need energy. [Adenosine triphosphate (ATP)](https://biologynotesonline.com/adenosine-triphosphate-atp/) or activated intermediate molecules supply energy in many biosynthetic reactions.

![Comparison of carbohydrate, protein, nucleic-acid, and lipid assembly and hydrolytic breakdown using their characteristic bonds and cellular mechanisms.](https://biologynotesonline.com/wp-content/uploads/2024/10/Formation-and-Breakdown-of-Major-Biomolecules-1024x768.webp)Comparison of carbohydrate, protein, nucleic-acid, and lipid assembly and hydrolytic breakdown using their characteristic bonds and cellular mechanisms.

### Breakdown of Larger Biomolecules

Breakdown of larger biomolecules occurs by breaking the bonds present between their smaller units. In many cases, water is added to break the bond. This process is called hydrolysis.

- Hydrolysis- Hydrolysis is the reverse of condensation reaction. Water enters into the bond and the large molecule splits into smaller units.The reaction is as follows-Polymer + H₂O → Smaller units

- Breakdown of carbohydrates- Glycosidic bonds are broken during carbohydrate breakdown. Starch, glycogen, or cellulose may break into smaller sugars. This process occurs by hydrolysis.

- Breakdown of proteins- Proteins are broken by cleavage of peptide bonds. The polypeptide chain is cut into smaller peptides or amino acids. Protease enzymes help in this reaction.

- Breakdown of nucleic acids- Nucleic acids are broken by cleavage of phosphodiester bonds. Nuclease enzymes break DNA and RNA into smaller nucleotide units.

- Breakdown of lipids- In lipid breakdown, ester bonds are hydrolyzed. Fats break into glycerol and fatty acids. Lipase enzymes help in this process.

- Role of enzymes- Enzymes control both formation and breakdown of biomolecules. Amylase breaks starch. Protease breaks protein. Lipase breaks lipid. Nuclease breaks nucleic acids.

Anabolism and catabolism- Formation of larger biomolecules is included under anabolism. Breakdown of larger biomolecules is included under catabolism. Catabolism gives small molecules which may enter energy pathways or can be used again for synthesis.

## Functions of Biomolecules

![Cell overview showing biomolecules in membrane structure, energy metabolism, enzyme catalysis, signaling, genetic information, and protein synthesis.](https://biologynotesonline.com/wp-content/uploads/2024/10/Functions-of-Biomolecules-in-the-Cell-1024x683.webp)Cell overview showing biomolecules in membrane structure, energy metabolism, enzyme catalysis, signaling, genetic information, and protein synthesis.

The following are some of the important functions of biomolecules-

- Energy production- Carbohydrates are a major source of energy for the cells. Glucose is broken down during [cellular respiration](https://biologynotesonline.com/cellular-respiration-equation/), and the released energy is used for the formation of adenosine triphosphate (ATP).

- Energy storage- Some biomolecules are stored as energy reserves. Starch stores glucose in plants, whereas [glycogen](https://biologynotesonline.com/glycogen-structure-functions-examples/) performs this function in animals. Lipids, mainly fats, are used for long-term energy storage.

- Structural function- Biomolecules form different structural components of cells and organisms. Cellulose gives structural support to plant cell walls, while proteins occur as structural components of cells and tissues. [Phospholipids](https://biologynotesonline.com/membrane-lipids/) form the major lipid component of cell membranes.

- Catalytic function- Many proteins act as [enzymes](https://biologynotesonline.com/enzymes/). These enzymes catalyze the chemical reactions taking place in biological systems.

- Storage and transfer of genetic information- [Deoxyribonucleic acid (DNA)](https://biologynotesonline.com/dna-definition-structure-properties-types-functions/) acts as the genetic material and carries biological information from one generation of cells to another. Ribonucleic acid (RNA) carries and uses this information in different cellular processes.

- Protein synthesis- Different forms of RNA take part in the synthesis of proteins. [Messenger RNA (mRNA)](https://biologynotesonline.com/mrna-structure/) carries the information from DNA to ribosomes, while ribosomal RNA and transfer RNA participate directly during protein synthesis.

- Transport of substances- Proteins are involved in transport and storage of different molecules. For example, hemoglobin transports oxygen in the blood.

- Cell signaling and regulation- Lipids and proteins can function as signaling molecules. Steroid hormones are derived from lipids, whereas some protein hormones are involved in transmitting information between cells.

- Cell recognition- Carbohydrate-containing molecules present on cell surfaces act as molecular markers. They participate in cell recognition, cell adhesion and interactions between neighboring cells.

- Defense- Some proteins perform protective functions. Antibodies are proteins involved in defense against infection.

## Examples of Biomolecules

Biomolecules are organic molecules present in living systems and are involved in cellular structure, energy, storage, catalysis and genetic information. They include small molecules such as glucose and nucleotides, as well as larger molecules like proteins and nucleic acids.

Some of the common examples of biomolecules are-

MoleculeBiomolecule classPrincipal biological roleGlucoseCarbohydrate (monosaccharide)It is an important source of energy. Glucose is broken down during cellular respiration for the formation of adenosine triphosphate (ATP).StarchCarbohydrate (polysaccharide)Starch is the storage form of glucose in plants. It is made up of glucose units mainly as amylose and amylopectin.GlycogenCarbohydrate (polysaccharide)It stores glucose in animals and occurs mainly in liver and muscle cells. Glycogen is highly branched.TriglycerideLipidTriglycerides are used for long-term energy storage, particularly in animals. A triglyceride contains glycerol joined with three fatty acids.PhospholipidLipidPhospholipids form the major structural material of cellular membranes. The molecules arrange into a bilayer because they contain both hydrophilic and hydrophobic regions.CholesterolLipid (sterol)Cholesterol occurs in animal cell membranes and helps in membrane properties. It is also a precursor for steroid hormones, vitamin D and bile salts.GlycineAmino acidIt is one of the amino acids used as a building block for proteins. Proteins are formed by polymerization of amino acids.HemoglobinProteinHemoglobin binds oxygen and carries most of the oxygen present in blood. It contains globin subunits with heme groups.EnzymesProteinMost enzymes are proteins that catalyze biochemical reactions in cells. They carry out a large number of chemical transformations required for cellular metabolism.Deoxyribonucleic acid (DNA)Nucleic acidDNA acts as the genetic material and stores biological information. Its nucleotide sequence provides information for the synthesis of specific proteins.Ribonucleic acid (RNA)Nucleic acidDifferent forms of RNA take part in protein synthesis and other cellular processes. Messenger RNA carries genetic information from DNA to the ribosomes.ATPNucleotideATP is the principal carrier of readily usable chemical energy in cells. It transfers energy during many cellular reactions.

## Biomolecules vs Biological Macromolecules

A biomolecule is a broader term for molecules associated with living organisms and biological processes. These include small molecules as well as large molecules. Biological macromolecules, on the other hand, are the large biomolecules.

![Size and scope comparison showing small biomolecules and large biological macromolecules, including proteins, nucleic acids, polysaccharides, and the special case of lipids.](https://biologynotesonline.com/wp-content/uploads/2024/10/Biomolecules-vs-Biological-Macromolecules-1024x512.webp)Size and scope comparison showing small biomolecules and large biological macromolecules, including proteins, nucleic acids, polysaccharides, and the special case of lipids.

A biomolecule does not always need to be a macromolecule. Glucose, amino acids, nucleotides and other small cellular molecules are biomolecules, whereas proteins and nucleic acids are large macromolecules.

FeatureBiomoleculesBiological MacromoleculesScopeIt is the broader biological term. It includes different molecules occurring or functioning in biological systems.These form a large-molecule group within biomolecules.Molecular sizeMay be small or large.Large molecules, often formed from smaller molecular units.ExamplesGlucose, amino acids, fatty acids, nucleotides, proteins, deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and other biological molecules.Proteins, DNA, RNA and polysaccharides are common examples.Polymer natureNo requirement of being a polymer. Small biomolecules can occur as individual molecules or act as building blocks.Many macromolecules are polymers. Proteins are made from amino acids, nucleic acids from nucleotides and polysaccharides from monosaccharides.TerminologyThe term describes molecules mainly by their biological occurrence or function.The term particularly indicates large molecular size.

Introductory biology commonly places carbohydrates, lipids, proteins and nucleic acids together under the four major classes of biological macromolecules. These groups form important cellular components and together account for much of the dry mass of cells.

There is a small terminology point with lipids. Proteins, nucleic acids and polysaccharides can form polymers from smaller units, whereas lipids are a diverse group and are not polymers in the same repeating-monomer sense. They are still commonly discussed along with the other biological macromolecules in introductory biology because lipids form a major group of large biological molecules with important cellular functions.

## Biomolecules at a Glance

Biomolecules are molecules associated with living cells and biological processes. The major organic biomolecules commonly studied are carbohydrates, lipids, proteins and nucleic acids.

BiomoleculeBasic unit / componentMajor bondMain functionCommon examplesCarbohydratesMonosaccharidesGlycosidic bondMajor source and storage of energy. Some carbohydrates also perform structural functions.Glucose, sucrose, starch, glycogen, celluloseLipidsMainly fatty acids and glycerol in fats. Lipids do not have a single repeating monomer.Ester bond in triglyceridesLong-term energy storage and formation of biological membranes. Some lipids act as hormones or their precursors.Triglycerides, phospholipids, cholesterol, steroidsProteinsAmino acidsPeptide bondProteins perform structural, catalytic, transport, regulatory and defensive functions. Many enzymes are proteins.Hemoglobin, collagen, insulin, enzymesNucleic acidsNucleotidesPhosphodiester bondStorage, transfer and expression of genetic information.Deoxyribonucleic acid (DNA), ribonucleic acid (RNA)

Adenosine triphosphate (ATP)- ATP is a nucleotide that acts as an immediate carrier of chemical energy in cells. It is not considered a separate major macromolecule class.

Quick exam point- Proteins and nucleic acids are polymers of amino acids and nucleotides, respectively. Polysaccharides are carbohydrate polymers of monosaccharides. Lipids are usually placed together with these biological macromolecules in introductory biology, but they are not polymers made from one repeating monomer in the same way.

## References

- Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2002). Molecular biology of the cell (4th ed.). Garland Science. [https://www.ncbi.nlm.nih.gov/books/NBK21054/](https://www.ncbi.nlm.nih.gov/books/NBK21054/)

- Clark, M. A., Douglas, M., & Choi, J. (2018). Biology 2e. OpenStax. [https://openstax.org/books/biology-2e/pages/3-1-synthesis-of-biological-macromolecules](https://openstax.org/books/biology-2e/pages/3-1-synthesis-of-biological-macromolecules)

- Cooper, G. M. (2000). The cell: A molecular approach (2nd ed.). Sinauer Associates. [https://www.ncbi.nlm.nih.gov/books/NBK9839/](https://www.ncbi.nlm.nih.gov/books/NBK9839/)

- Fowler, S., Roush, R., & Wise, J. (2013). Concepts of biology. OpenStax. [https://openstax.org/books/concepts-biology/pages/2-3-biological-molecules](https://openstax.org/books/concepts-biology/pages/2-3-biological-molecules)

- Pittman, R. N. (2011). Regulation of tissue oxygenation. Morgan & Claypool Life Sciences. [https://doi.org/10.4199/C00029ED1V01Y201103ISP017](https://doi.org/10.4199/C00029ED1V01Y201103ISP017)

- Rye, C., Wise, R., Jurukovski, V., DeSaix, J., Choi, J., & Avissar, Y. (2016). Biology. OpenStax. [https://openstax.org/books/biology/pages/3-3-lipids](https://openstax.org/books/biology/pages/3-3-lipids)