Biology Short Notes: Cell division and Biomolecules

By BYJU'S Exam Prep

Updated on: September 25th, 2023

This article is the part of our SSC CGL Study Plan. As per the current trend of competitive exams, the weightage of science has been increased. In this article, we will be covering important concepts of cell division and Biomolecules.

This article is the part of our SSC CGL Study Plan. As per the current trend of competitive exams, the weightage of science has been increased. In this article, we will be covering important concepts of cell division and Biomolecules.

 Cell Division

A cell is the basic structural and functional part of the body. It requires energy to survive and grow. After a stage of growth, it divides into daughter cells to form new cells in order to repair worn-out or damaged tissues throughout an organism.

Types of Cell Divisions

Mitosis:  Mitosis is the type of cell division by which a single cell divides in such a way as to produce two genetically identical daughter cells. This is the method by which the body produces new cells for both growth and repair of ageing or damaged tissues throughout the body.  

Meiosis: Meiosis, which is also referred to as reduction division, is the form of cell division in which a cell divides into four daughter cells each of which has half of the number of chromosomes of the original cell.  

 The main differences between the two types of cell division are:



One step

Two steps

Two daughter cells produce

Four daughter cells

An exact copy of parent cell genetically

Different from parent cell genetically

Number of chromosome same

Half of the chromosome

It takes place in the somatic or vegetative
cells of all living things and no crossing over can take place in it

It takes place in the reproductive or gonadic cells. A successfully crossing-over can take place between the non-sister chromatids. At least one crossover of DNA takes place during a meiotic cell division.

Prophase, prometaphase, metaphase, anaphase, telophase and Cytokinesis are the major phases of mitotic cell division.

Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II and Telophase II are the main steps of Meiosis


Biomolecules are the organic compounds which form the basis of life, i.e., they build up the living system and responsible for their growth and maintenance. The sequence that relates biomolecules to a living organism is

Biomolecules → Organelles → Cells → Tissues → Organs → Living organism.

Types of Biomolecules

Class 1: Carbohydrates

Carbohydrates are the most abundant organic molecules in nature. They are primarily composed of the elements carbon, hydrogen and oxygen. The name carbohydrate literally means ‘hydrates of carbon’. The term ‘sugar’ is applied to carbohydrates soluble in water and sweet to taste.

Functions of carbohydrates:

  • They are the most abundant dietary source of energy for all organisms.
  • Carbohydrates are precursors for many organic compounds (fats, amino acids).
  • Carbohydrates (as glycoproteins and glycolipids) participate in the structure of cell membrane and cellular functions such as cell growth, adhesion and fertilization.
  • Carbohydrates also serve as the storage form of energy (glycogen) to meet the immediate energy demands of the body.

They are broadly classified into three groups- monosaccharide’s, oligosaccharides and polysaccharides. This categorization is based on the number of sugar units.


Monosaccharide’s (Greek: mono-one) are the simplest group of carbohydrates and are often referred to as simple sugars. They have the general formula Cn(H2O)n, and they cannot be further hydrolysed. Based on the number of carbon atoms, the monosaccharide’s are regarded as trioses (3C), tetroses (4C), pentoses (5C), hexoses (6C) and heptoses (7C).

Derivatives of Monosaccharide’s: Amino sugars, Deoxysugars, L-Ascorbic acid (vitamin C)


Oligosaccharides (Greek: oligo-few) contain 2-10 monosaccharide molecules which are liberated on hydrolysis. Based on the number of monosaccharide units present, the oligosaccharides are further subdivided to disaccharides, tri-saccharides etc.

Among the oligosaccharides, disaccharides are the most common.

  • Reducing disaccharides with free aldehyde or keto group e.g. maltose, lactose.
  • Non-reducing disaccharides with no free aldehyde or keto group e.g. sucrose, trehalose.


Polysaccharides (Greek: poly-many) are poly­mers of monosaccharide units with high molecular weight (up to a million). They are usually tasteless (non-sugars) and form colloids with water. Poly­saccharides are of two types- homopoly- saccharides and hetero-polysaccharides, e.g. Starch, Glycogen, and Cellulose.   

Class 2 Lipids

Lipids may be regarded as organic substances relatively insoluble in water, soluble in organic solvents (alcohol, ether etc.), actually or potentially related to fatty acids and utilized by the living cells. Unlike the polysaccharides, proteins and nucleic acids, lipids are not polymers. They are mostly small molecules.

Functions of Lipids:

  • Lipids perform several important functions:
  • They are the concentrated fuel reserve of the body (triacylglycerol’s).
  • Lipids are the constituents of membrane structure and regulate the membrane permeability (phospholipids and cholesterol).
  • They serve as a source of fat-soluble vitamins (A, D, E and K).
  • Lipids are important as cellular metabolic regulators (steroid hormones and prostaglandins).

Classification of Lipids:

  1. Simple lipids: Esters of fatty acids with alcohols

These are mainly of two types:

  • Fats and oils (triacylglycerol’s): These are esters of fatty acids with glycerol. The difference between fat and oil is only physical. Thus, oil is a liquid while fat is a solid at room temperature.
  • Waxes: Esters of fatty acids (usually long-chain) with alcohols other than glycerol.
  1. Complex (or compound) lipids: Esters of fatty acids with alcohols containing additional groups such as phosphate, a nitrogenous base, carbohydrate, protein etc.
  2. Derived lipids: These are the derivatives obtained on the hydrolysis of group I and group 2 lipids which possess the characteristics of lipids. These include glycerol and other alcohols, fatty acids, mono- and diacylglycerols, lipid-soluble vitamins, steroid hormones, hydrocarbons and ketone bodies.
  3. Miscellaneous lipids: These include a large number of compounds possessing the characteristics of lipids e.g., carotenoids, hydrocarbons such as pentacosane (in beeswax), terpenes etc.
  4. Neutral lipids: The lipids which are uncharged are referred to as neutral lipids. These are mono, di-, and triacylglycerol’s, cholesterol and cholesteryl esters.

Class 3: Amino Acids

The compounds containing an amino group (-NH2) and carboxylic group (-COOH) are called amino acids.

A human body can synthesise ten amino acids, called non-essential amino acids. The remaining ten amino acids required for protein synthesis are not synthesised by the body and are called essential amino acids. They are: Phenylalanine, Histidine, Tryptophan, Valine, Methionine, Threonine, Arginine, Lucien, Isoleucine and Lysine

Peptides: Peptides are condensation products of two or more amino acids

Proteins:  Condensation Products of many amino acids (≈ 10000) is Known as polypeptide and those polypeptides which have a molecular mass above than 10000 are called proteins.

Structure of Proteins

  • Primary structure It simply reveals the sequence of amino acids.
  • Secondary structure α-helix structure maintained by hydrogen bonds or β-pleated sheet Structure when R is a small group.
  • Tertiary structure the folding and superimposition of polypeptide chains form a compact Globular shape, termed as tertiary structure. It is stabilised by covalent, ionic, hydrogen and Disulphide bonds

Classification on the Basis Functions

  • Structural proteins: Fibrous proteins
  • Enzymes: Serve as a biological catalyst e.g., pepsin, trypsin etc.
  • Hormones Insulin
  • Contractile proteins Found in muscles, e.g., myosin, actin.
  • Antibodies Gamma globulins present in the blood.
  • Blood protein haemoglobin and fibrinogen
  • Denaturation of Proteins The process that changes the three-dimensional structure of native proteins is called denaturation of proteins. It can be caused by Change in pH, addition of electrolyte, heating or addition of solvents like water, alcohol or acetone.

Tests of Proteins

(i) Biuret Test

Protein solution + NaOH + dil. CuSO4 → pink or violet colour.

(ii) Millon’s Test

Protein solution + Million’s reagent → pink colour

Million’s reagent is a solution of mercuric nitrate and nitrite in nitric acid containing traces of nitrous acid.           

(iii) Iodine reaction

Protein solution + iodine in potassium iodide solution → yellow colour

(iv) Xanthoproteic test:

Protein Solution + Conc. HNO3 → Yellow colour + NaOH → Orange colour

Enzymes: Enzymes constitute a group of complex proteinoid compounds, produced by living organisms which catalyse the chemical reaction. Non-portentous components enhance the activity of certain enzymes and are known as coenzymes. These include metal ions like Mn2+, Mg2+, K+, Na+, Zn2+, Co2+ etc.

Mechanism of Enzyme Action

Enzyme + Substrate → [Enzyme substrate] → Product + Enzyme Activated complex

Nucleic Acids:  Nucleic acid is a polynucleotide, present in the living cells or bacterial cells having no nucleus and in viruses having no cells.

 Functions of Nucleic Acids

  • Direct the synthesis of proteins.
  • Transfer the genetic information (hereditary characters)

DNA: Deoxyribonucleic acid.

DNA + H2O → Phosphoric acid + Deoxyribose + A, G, C, T

RNA Ribonucleic acid

RNA + H2O → Phosphoric acid + Ribose + A, G, C, U

Structure of DNA

It consists of two polynucleotide chains, each chain form a right-handed helical spiral with ten bases in one turn of the spiral. The two chains coil to double helix and run in the opposite direction. These are held together by hydrogen bonding.

Structure of RNA

It is usually a single strand of ribonucleotides and takes up right-handed helical conformation. Up to 12000 nucleotides constitute RNA. It can base pair with complementary strands of DNA or RNA according to standard base-pairing rules-G pairs with C, A pairs with U or T. The paired strands in RNA-RNA or RNA-DNA are anti-parallel as in DNA.


The organic compounds other than carbohydrates, proteins and fats which are required by the body to maintain normal health, growth and nutrition are called vitamins. The vitamins are complex organic molecules. They are represented by letters such as A, B, C, D, E, K.

Vitamins are broadly classified into two types

  • Water-soluble vitamins and
  • Oil-soluble vitamins.

Vitamins A, D, E and K are oil-soluble whereas vitamins B and C are water-soluble. Vitamin H is neither fat-soluble nor water-soluble

These are the most important biomolecules for examination point of view. Try to understand each and every point of this article. And after this article, try to attempt Gradeup quizzes on this topic so that you feel comfortable in this topic.

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