Written By Jyotirmayee Nayak
Last Modified 18-01-2023

Biomolecules: Definition, Types & Functions

Biomolecules: Do you know what a cell is composed of? Can you name some organic and inorganic substances which are present inside the cell? A cell is composed of a variety of atoms like carbon, hydrogen, oxygen, etc., which form the components of many biologically important molecules. These biomolecules, which are present in the cells of an organism, help in the growth and development of our body as well as provide immunity against attacking pathogens. Read this article to explore the different types of biomolecules and their importance in the body of living organisms.

What Do You Mean by Biomolecules?

Biomolecules can be defined as non-living organic substances (e.g., carbohydrates, proteins, lipids, vitamins and nucleic acids) that play an important role in the structure and function of living organisms. They are also involved in the maintenance and metabolic processes of living organisms.

What Are the Types of Biomolecules?

Biomolecules are divided into five major types:

Carbohydrates
Proteins
Lipids
Nucleic Acid
Vitamins

1. Carbohydrates

a) Carbohydrates are organic compounds mainly composed of \(C, H\) and \(O.\)

b) Chemically they are polyhydroxy aldehydes or polyhydroxy ketones.

c) They are produced directly by the green plants during photosynthesis.

d) They are also known as saccharides or sugars.

e) On the basis of their reducing properties, carbohydrates can be of two types, i.e.,

i) Reducing sugars: These sugars have aldehyde or ketone groups which act as reducing agents for solutions like Tollen’s reagent, Fehling’s solution and Benedict’s reagent. For example- glucose, fructose, lactose, etc.
ii) Non-reducing sugars: These sugars do not have any aldehyde or ketone groups due to which they do not act as reducing agents for solutions like Tollen’s reagent, Fehling’s solution and Benedict’s reagent. For example- Sucrose, Polysaccharides, etc.

f) Carbohydrates are also classified into other two types, i.e.,

i) Sugars: These are sweet tasting soluble carbohydrates that include mostly monosaccharides such as glucose, fructose, galactose, etc. and disaccharides such as lactose and sucrose.
ii) Non-sugars: These do not have any sweet taste and are insoluble in water that mostly includes polysaccharides such as starch and cellulose.

On the basis of hydrolysis, carbohydrates can be classified into three types:

i) Monosaccharides
a) These are the simplest carbohydrates that cannot be hydrolysed further into smaller components.
b) These are generally composed of three to seven carbon atoms per molecule.
c) Based on the type of functional group attached to them, monosaccharides are classified into two types

i) Aldoses: When the functional group in a monosaccharide is aldehyde \(\left({ – CHO – } \right)\), they are known as aldoses, e.g., glyceraldehyde, glucose, ribose, etc.

ii) Ketoses: When the functional group in the monosaccharide is a keto group \(\left({ – CO – } \right)\), they are referred to as ketosis, e.g., ribulose, fructose, etc.

They can reduce the cupric ions \(\left({C{u^{2 + }}} \right)\) of Benedict’s or Fehling’s solution to cuprous ions \(\left({C{u^{ + }}} \right)\) and can reduce Tollen’s reagent too.
For example- Ribose, Glucose, Erythrose, etc.

ii) Oligosaccharides
a) These are formed by the condensation of \(2-10\) monosaccharide units held together by glycosidic bonds.
b) On hydrolysis, they produce two or more molecules either of the same or different types of monosaccharides.
c) They are crystalline, water-soluble and sweet in taste.
d) On the basis of the number of monosaccharide units they produce on hydrolysis, they are categorised into disaccharide, trisaccharide and tetrasaccharide, etc.
e) For example- Sucrose, Maltose, Lactose, Raffinose, etc.
iii) Polysaccharides
a) These are the macromolecules that are formed of long chains of sugars composed of more than \(10\) monosaccharide units.
b) They are also called non-sugars as they do not have a sweet taste and are insoluble in water.
c) The polysaccharide chain is made up of two ends; the right end is called the reducing end because of the presence of a functional group that is not involved in the formation of glycosidic bond with other sugar molecules, whereas the left end is called the non-reducing end because of the absence of functional group.
d) On the basis of the type of monosaccharide units, they are mainly classified into two types-
i) Homopolysaccharides: These are made up of only one type of monosaccharide unit. For example- Cellulose, Starch, Glycogen, etc.
Starch is a polysaccharide that is composed of amylose and amylopectin. When iodine solution is added to the starch, then amylose reacts with iodine to give a blue-black colour.
ii) Heteropolysaccharides: These are the polysaccharides that are made up of two or more types of monosaccharide units. For example- Glycoproteins, Glycolipids, etc.
Mucopolysaccharides are also heteropolysaccharides composed of hexosamines and non-nitrogenous sugars linked by glycosidic bonds.

Fig: Classification of Carbohydrates

2. Proteins

Proteins form the most abundant and important intracellular organic biomolecules.
These are the polypeptide chains of amino acids that are linked by peptide bonds or amide linkages.
There are four different types of protein structure:
a) Primary: It forms the basic structure of the protein that is formed by the linkage of amino acids in a linear sequence after the completion of the translation process.
b) Secondary: It is formed by the folding of the primary structure of the protein that is stabilised by hydrogen bonds. It is of two types- \(\alpha \)-helix and \(\beta \)- pleated sheets—for example- Keratin, Silk fibre.
c) Tertiary: The three-dimensional arrangement of helices and sheets forms the tertiary structure of a protein which is stabilised by several types of bonds like hydrogen bonds, ionic bonds, Van der Waals interactions, covalent bonds and hydrophobic bonds. For example- enzymes.
d) Quaternary: Most of the proteins contain multiple helices and sheets, and the entire aggregation of them with three-dimensional foldings make the quaternary structure of a protein. It is formed by the assembly of more than one polypeptide chain or subunits—for example, haemoglobin.
On the basis of the tertiary structure of the protein, proteins are classified into two types- i)
i) Fibrous proteins: These have long fibre-like structures having more structural roles.
Examples: Keratin, collagen, elastin, fibrinin, etc.
ii) Globular proteins: These have spherical or rounded structures having more functional roles. Examples: Albumin, globulin, histones, etc.
If proteins are exposed to an extreme change in \(pH\), acids or temperature or bases or high salt concentration, the weak bonds holding the tertiary and quaternary structure get disrupted, and the protein gets unfolded into the primary structure. This unfolding is known as the denaturation of proteins.
A denatured protein may spontaneously refold into its original structure when suitable conditions are given. This is called renaturation.

Fig: Types of Protein Structure

3. Lipids

Lipids are the organic macromolecules that are esters of fatty acids and alcohol, which are generally insoluble in water and soluble in organic solvents.
They are classified into the following types:
a) Simple Lipids:
They are the esters of fatty acids and various alcohol. They are further subdivided into two types, i.e.,
i) Fats and oils: These are esters of fatty acids with glycerol and are also known as glycerides. Fats are mostly derived from animals that are solid at room temperature, whereas oils are mostly derived from plants that are liquid at room temperature.
ii) Waxes: These are esters of fatty acids with alcohols other than glycerols.
b) Compound or Conjugated Lipids
These are the esters of saturated or unsaturated fatty acids with glycerol but also contain other substances like carbohydrate, amino acid, phosphoric acid, etc.
c) Derived Lipids
These include lipid-like substances such as sterol or derivatives of lipids, e.g., steroids, prostaglandins and terpenes.

Fig: Classification of Lipids

4. Nucleic Acids

a) These constitute the genetic material of all living organisms.
b) There are two types of nucleic acids present in the living cell, i.e., deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
c) Both DNA and RNA were discovered by Friedrich Miescher in \(1969\).
d) These are the macromolecules made up of monomeric units called nucleotides which are joined by phosphodiester bonds.
e) Nucleotides are composed of three molecules, i.e., phosphoric acid, pentose sugar and nitrogenous bases (adenine, guanine, thymine, uracil, and cytosine).
f) DNA consists of adenine, guanine, cytosine and thymine nitrogenous bases, whereas RNA consists of adenine, guanine, cytosine and uracil.
g) The sugar molecule and the nitrogenous base together form the nucleoside that combines with one or more phosphate groups to form the nucleotide.
\({\text{Nucleoside}}\,{\text{ + }}\,{\text{Phosphate}}\, {\text{group}}\, {\text{=}}\, {\text{Nucleotide}}\)
i) DNA
a) It is present as the main genetic material in the majority of organisms, including prokaryotes, eukaryotes and certain viruses.
b) In prokaryotes, it is present without any association with proteins, whereas in eukaryotes, it is present with proteins like histones.
c) It is found in the chromosomes of the nucleus, having a double-stranded structure. The two strands are spirally coiled in opposite directions.
d) It is a long molecule with a high molecular weight.
e) The most widely accepted structural model of DNA is the double-stranded double-helical model of Watson and Crick and Wilkins \((1953)\).
ii) RNA
a) It is another nucleic acid present in the cell found predominantly in the cytoplasm, nucleolus and nucleoplasm.
b) It is mostly present in a single-stranded polynucleotide form except for few viruses where they have double-stranded RNA.
c) It is a relatively short molecule with low molecular weight.
d) RNA is divided into three types, i.e., messenger RNA, ribosomal RNA and transfer RNA.

Fig: Types of Nucleic Acids

5. Vitamins

a) Vitamins are organic molecules required by an organism in small quantities for the proper functioning of metabolism.
b) Vitamins are the essential nutrients that cannot be synthesised in the organism, and therefore must be obtained through the diet.
c) Vitamins are classified into two types on the basis of their solubility in water, i.e., water-soluble vitamins and fat-soluble vitamins.
d) In humans, there are \(13\) vitamins, out of which \(4\) are fat-soluble vitamins (\(A,D,E\) & \(K\)) and \(9\) are water-soluble vitamins (\(8-B\) vitamins and vitamin \(C\)).
e) Water-soluble vitamins are easily soluble in water and are readily excreted out from the body, whereas fat-soluble vitamins are absorbed through the intestinal tract with the help of lipids or fats.
f) Vitamins have diverse biochemical functions.

Biomolecules Functions

The functions of biomolecules are as follows:
A. Carbohydrates
i) Carbohydrates act as structural components in the cell wall of plants, fungi, bacteria and protists, e.g., cellulose and chitin.
ii) Carbohydrates also act as the reserve food material in plants (starch) and in animals (glycogen).
iii) Carbohydrates help in the lubrication of joints between bones, e.g., hyaluronic acid.

B. Proteins
i) Carrier proteins help in the transportation of nutrients across the cell membrane.
ii) Antibodies and interferons are proteins that help in fighting various infectious organisms.
iii) Proteins like actin and myosin help in the movement of muscles.
iv) Proteins also help in blood clotting at the time of injury.
v) Proteins also help in the growth and repair of body tissues.

C. Fats
i) Fats or lipids act as the reserve food materials in mammals that provide insulation to the body.
ii) Fats also act as shock-absorbing cushions in eyeballs and kidneys.

D. Nucleic Acids
i) Nucleic acids enable a cell to grow, maintain and divide by directing the synthesis of structural proteins.
ii) Nucleic acids act as the genetic material that transfers hereditary characters from one generation to the next.

E. Vitamins
i. Vitamin \(A\) helps in the development of pigment of rod cells.
ii. The \(B\)-complex vitamins function as coenzymes.
iii. Vitamin \(D\) regulates the mineral metabolism for bones and other organs.
iv. Vitamin \(C\) and \(E\) function as antioxidants.

Summary

Biomolecules are non-living organic substances (e.g., carbohydrates, proteins, lipids, vitamins and nucleic acids) that play an important role in the structure and function of living organisms. They are also involved in the maintenance and metabolic processes of living organisms. Biomolecules are mainly divided into five types- carbohydrates, proteins, lipids, nucleic acids and vitamins. Thus, all the carbon compounds that we get from the living tissues are called biomolecules. Carbohydrates, proteins and fats play an important role in the structure and function of living organisms, whereas nucleic acids act as the genetic material that transfers hereditary characters from one generation to the next. Vitamins have diverse biochemical functions.

FAQs

Q.1. What is the simple definition of biomolecules?
Ans: Biomolecules can be defined as non-living organic substances (e.g., carbohydrates, proteins, lipids and nucleic acids) that play an important role in the structure and function of living organisms.

Q.2. What is the importance of biomolecules?
Ans: a. Carbohydrates act as structural components in the cell wall of plants, certain fungi, bacteria and protists, e.g., cellulose and chitin.
b. Proteins also help in fighting infectious organisms like antibodies.
c. Fats or lipids act as the reserve food materials in mammals that provide insulation to the body.
d. Nucleic acids enable a cell to grow, maintain and divide by directing the synthesis of structural proteins.
e. Vitamin \(A\) helps in regulating the growth and differentiation of cells and tissue.

Q.3. Give some examples of biomolecules.
Ans: Carbohydrates- glucose, fructose, starch, etc.
Proteins- actin, myosin, collagen, etc.
Lipids- steroids, terpenes, waxes, etc.
Nucleic Acids- DNA and RNA.
Vitamins- Vit \(A, B, C, D, E\) and \(K\).

Q.4. Which biomolecules are found in fruits?
Ans: In fruits, mainly carbohydrates are found in the form of fructose.

Q.5. What do all biomolecules have in common?
Ans: All the biomolecules are organic molecules consisting of carbon, hydrogen and oxygen.

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