Class 12 Chemistry Biomolecules Notes

Carbohydrates
Monosaccharides
Glucose & Fructose
Disaccharides
Polysaccharides
Proteins
Enzymes
Vitamins
Nucleic Acids
Hormones
Chapter Summary
Important Differences
Exam Questions
Mind Map

Part 1: Carbohydrates

Chapter Overview

Biomolecules are the chemical substances that make up living organisms. Among them, carbohydrates are the most abundant organic compounds found in nature. They are produced mainly by green plants during photosynthesis and serve as the primary source of energy for almost all living organisms.

1. What are Carbohydrates?

Definition

Carbohydrates are polyhydroxy aldehydes, polyhydroxy ketones, or compounds that produce them on hydrolysis.

They are commonly known as sugars or saccharides.

Important Point

Earlier, carbohydrates were believed to be hydrates of carbon because many have the general formula:

Cx(H₂O)y

However, this formula is not a true definition because:

Some compounds satisfy the formula but are not carbohydrates.

Some carbohydrates do not follow this formula.

Examples

Carbohydrate	Common Name
Glucose	Blood sugar
Fructose	Fruit sugar
Sucrose	Cane sugar
Lactose	Milk sugar
Maltose	Malt sugar
Starch	Plant storage food
Cellulose	Plant cell wall material
Glycogen	Animal starch

Why are Carbohydrates Important?

Carbohydrates perform several essential functions.

1. Main Source of Energy

Glucose is the body’s preferred energy source.
Cells break down glucose during respiration to produce ATP.

2. Energy Storage

Plants store carbohydrates as:

➡ Starch

Animals store carbohydrates as:

➡ Glycogen

3. Structural Role

Cellulose forms the rigid cell wall of plants.

4. Industrial Importance

Carbohydrates are used in making:

Paper
Cotton cloth
Textiles
Wood products
Brewing industries

5. Biological Importance

Certain sugars like ribose and deoxyribose are components of nucleic acids (RNA and DNA).

Classification of Carbohydrates

Carbohydrates are classified according to the products formed during hydrolysis.

                Carbohydrates
                      │
      ┌───────────────┼───────────────┐
      │               │               │
Monosaccharides   Oligosaccharides  Polysaccharides

1. Monosaccharides

Definition

Monosaccharides are the simplest carbohydrates that cannot be hydrolysed into smaller carbohydrate units.

These are also called simple sugars.

Characteristics

Sweet in taste
Water soluble
Colourless crystalline solids
Reducing sugars
Immediate source of energy

Examples

Glucose
Fructose
Ribose
Galactose

Classification of Monosaccharides

Based on Functional Group

Type	Functional Group	Example
Aldose	Aldehyde (-CHO)	Glucose
Ketose	Ketone (>C=O)	Fructose

Based on Number of Carbon Atoms

Carbon Atoms	Name
3	Triose
4	Tetrose
5	Pentose
6	Hexose
7	Heptose

Examples

Ribose → Pentose
Glucose → Hexose
Fructose → Ketohexose

2. Oligosaccharides

Definition

Carbohydrates that produce 2–10 monosaccharide molecules on hydrolysis are called oligosaccharides.

The most common members are disaccharides.

Examples

Sucrose
Maltose
Lactose

3. Polysaccharides

Definition

Polysaccharides produce a large number of monosaccharides when hydrolysed.

Characteristics

Not sweet
Generally insoluble in water
High molecular weight
Storage and structural carbohydrates

Examples

Starch
Cellulose
Glycogen

Classification Based on Reducing Property

Carbohydrates are also classified as reducing and non-reducing sugars.

Reducing Sugars

These reduce:

Fehling’s solution
Tollens’ reagent

Examples:

Glucose
Fructose
Maltose
Lactose

Non-Reducing Sugars

Do not reduce these reagents.

Example:

Sucrose

Quick Comparison Table

Property	Monosaccharides	Oligosaccharides	Polysaccharides
Hydrolysis	Cannot be hydrolysed	Gives 2–10 units	Gives many units
Sweet Taste	Yes	Usually yes	No
Solubility	High	High	Low
Molecular Size	Small	Medium	Very large
Examples	Glucose	Sucrose	Starch

NCERT Important Points

✔ Carbohydrates are mainly produced by plants.

✔ Chemically, carbohydrates are polyhydroxy aldehydes or ketones.

✔ Monosaccharides are reducing sugars.

✔ Polysaccharides are also called non-sugars because they are not sweet.

✔ Starch is the storage carbohydrate of plants.

✔ Glycogen is the storage carbohydrate of animals.

✔ Cellulose is the main component of plant cell walls.

Memory Tricks

Types of Carbohydrates

MOP

M → Monosaccharides
O → Oligosaccharides
P → Polysaccharides

Storage Forms

Plant → Starch

Animal → Glycogen

Structural Carbohydrate

Cellulose → Cell Wall

Part 2: Monosaccharides — Glucose and Fructose

1. Glucose

Introduction

Glucose is one of the most important monosaccharides.

Common Names:

Blood sugar
Dextrose

Classification:

Glucose is:

A monosaccharide
An aldohexose
A reducing sugar
A member of the D-series

Molecular Formula:

$C_6H_{12}O_6$ C6H12O6

Glucose occurs naturally in:

Sweet fruits
Honey
Ripe grapes

It is also a basic unit of many carbohydrates such as:

Starch
Cellulose

2. Preparation of Glucose

(A) From Sucrose (Cane Sugar)

When sucrose is heated with dilute mineral acids like:

HCl
H₂SO₄

it undergoes hydrolysis and produces equal amounts of:

Glucose
Fructose

Reaction:

Sucrose + Water → Glucose + Fructose

(B) From Starch

Commercial glucose is prepared by hydrolysis of starch.

Conditions:

Dilute H₂SO₄
Temperature: 393 K
Pressure: 2–3 atm

Reaction:

Starch + Water → Glucose

3. Structure of Glucose

The structure of glucose was determined by studying its chemical reactions.

Evidence for Open Chain Structure

1. Molecular Formula

The molecular formula of glucose was found to be: $C_6H_{12}O_6$ C6H12O6

This indicates the presence of six carbon atoms.

2. Formation of n-Hexane

On prolonged heating with HI:

Glucose gives n-hexane.

Conclusion:

All six carbon atoms are arranged in a straight chain.

3. Presence of Carbonyl Group

Glucose reacts with:

Hydroxylamine
Hydrogen cyanide (HCN)

to form addition products.

Conclusion:

Glucose contains a carbonyl group (>C=O).

4. Presence of Aldehyde Group

Glucose reacts with bromine water and gets oxidised to:

Gluconic acid

Conclusion:

The carbonyl group in glucose is an aldehyde group.

Therefore glucose is an aldohexose.

5. Presence of Five Hydroxyl Groups

Glucose reacts with acetic anhydride to form:

Glucose pentaacetate

Conclusion:

Glucose contains five –OH groups.

6. Presence of Primary Alcohol Group

Oxidation of glucose with nitric acid gives:

Saccharic acid

Conclusion:

Glucose contains a primary alcoholic group.

Open Chain Structure of Glucose

According to Fischer projection:

        CHO
         |
    H — C — OH
         |
    OH— C — H
         |
    H — C — OH
         |
    H — C — OH
         |
       CH2OH

This structure explains many properties of glucose.

However, some observations could not be explained by this structure.

4. Limitations of Open Chain Structure

The open-chain structure failed to explain:

(1) Absence of Aldehyde Reactions

Although glucose contains an aldehyde group, it:

Does not give Schiff’s test
Does not form sodium bisulphite addition product

(2) No Reaction of Pentaacetate with Hydroxylamine

Glucose pentaacetate does not react with hydroxylamine.

This suggests that a free aldehyde group is absent.

(3) Existence of Two Forms

Glucose exists in two crystalline forms:

α-glucose

Melting point: 419 K

β-glucose

Melting point: 423 K

The open-chain structure cannot explain these two forms.

5. Cyclic Structure of Glucose

To explain these observations, it was proposed that glucose forms a cyclic structure.

Ring Formation

The –OH group at carbon number 5 attacks the aldehyde group at carbon number 1.

This produces a cyclic hemiacetal.

Important:

Glucose forms a six-membered ring.

This structure is called:

Pyranose Structure

because it resembles the cyclic compound pyran.

6. Anomers of Glucose

The two cyclic forms of glucose differ only in the arrangement of the –OH group at carbon-1.

Carbon-1 is called:

Anomeric Carbon

The two forms are:

α-D-Glucose

OH group at C-1 has one orientation

β-D-Glucose

OH group at C-1 has opposite orientation

These two forms are called:

Anomers

Definition:

Isomers that differ only in the configuration around the anomeric carbon are called anomers.

7. D and L Configuration of Glucose

The letters D and L represent the configuration of a molecule.

They are not related to:

(+) or (–) optical rotation

D-Configuration:

The –OH group on the lowest asymmetric carbon is on the right side.

L-Configuration:

The –OH group is on the left side.

Glucose has:

D-(+)-Glucose

Meaning:

D → Configuration
(+) → Dextrorotatory nature

8. Fructose

Introduction

Fructose is another important monosaccharide.

Common Name:

Fruit sugar

Sources:

Fruits
Honey
Vegetables

Classification:

Fructose is:

A monosaccharide
A ketohexose
A reducing sugar
A member of D-series

Molecular Formula:

$C_6H_{12}O_6$ C6H12O6

Fructose is written as:

D-(–)-Fructose

because it is laevorotatory.

9. Structure of Fructose

Fructose contains:

Six carbon atoms
Ketone group at carbon number 2

Therefore, it is a:

Ketohexose

Cyclic Structure of Fructose

Fructose forms a cyclic structure by reaction between:

C-5 hydroxyl group
C-2 keto group

This forms a:

Five-membered ring

called:

Furanose Structure

because it resembles furan.

Glucose vs Fructose (Important Difference)

Property	Glucose	Fructose
Formula	C₆H₁₂O₆	C₆H₁₂O₆
Type	Aldohexose	Ketohexose
Functional group	Aldehyde	Ketone
Carbonyl position	C-1	C-2
Common name	Dextrose	Fruit sugar
Optical nature	D-(+)	D-(–)
Ring structure	Pyranose	Furanose

Important Exam Points ⭐

Remember:

Glucose

Aldohexose
Pyranose ring
Six-membered cyclic structure
Forms α and β anomers

Fructose

Ketohexose
Furanose ring
Five-membered cyclic structure

Part 3: Disaccharides and Polysaccharides

1. Disaccharides

Definition

Disaccharides are carbohydrates that produce two monosaccharide molecules on hydrolysis.

They are formed when two monosaccharide units join together by a bond called:

Glycosidic Linkage

Definition:

A glycosidic linkage is an oxygen bridge formed between two monosaccharide molecules by the loss of a water molecule.

Formation:

Monosaccharide + Monosaccharide → Disaccharide + Water

Example:

Glucose + Fructose → Sucrose + H₂O

Reducing and Non-Reducing Disaccharides

Disaccharides are classified according to the presence of free aldehyde or ketone groups.

1. Reducing Sugars

Definition:

Disaccharides that contain a free reducing group are called reducing sugars.

They can reduce:

Fehling’s solution
Tollens’ reagent

Examples:

Maltose
Lactose

2. Non-Reducing Sugars

Definition:

Disaccharides in which reducing groups are involved in glycosidic bond formation are called non-reducing sugars.

Example:

Sucrose

2. Sucrose

Introduction

Sucrose is one of the most common disaccharides.

Common Name:

Cane sugar

Sources:

Sugar cane
Sugar beet

Composition

Sucrose is made up of:

One molecule of α-D-glucose
One molecule of β-D-fructose

Hydrolysis:

Sucrose + Water → Glucose + Fructose

Glycosidic Bond in Sucrose

The linkage occurs between:

C-1 of α-D-glucose
C-2 of β-D-fructose

Because both reducing groups participate in bond formation:

➡ Sucrose is a non-reducing sugar.

Invert Sugar

Sucrose is:

Dextrorotatory (+)

After hydrolysis:

Glucose → Dextrorotatory (+)
Fructose → Laevorotatory (–)

Since fructose has stronger negative rotation, the mixture becomes:

➡ Laevorotatory

This hydrolysed product is called:

Invert Sugar

3. Maltose

Introduction

Maltose is a disaccharide consisting of:

Two α-D-glucose units

Linkage

The two glucose molecules are joined by:

α(1 → 4) glycosidic linkage

Meaning:

C-1 of first glucose joins with
C-4 of second glucose

Reducing Nature

The second glucose molecule has a free aldehyde group.

Therefore:

➡ Maltose is a reducing sugar.

4. Lactose

Introduction

Lactose is commonly known as:

Milk Sugar

It is found in milk.

Composition

Lactose contains:

β-D-galactose
β-D-glucose

Linkage

The bond is between:

C-1 of galactose
C-4 of glucose

Reducing Nature

A free aldehyde group can develop in glucose.

Therefore:

➡ Lactose is a reducing sugar.

Comparison of Disaccharides

Property	Sucrose	Maltose	Lactose
Common name	Cane sugar	Malt sugar	Milk sugar
Components	Glucose + Fructose	Glucose + Glucose	Galactose + Glucose
Linkage	α-D-glucose C1 → β-D-fructose C2	α-glucose C1 → glucose C4	β-galactose C1 → glucose C4
Reducing nature	Non-reducing	Reducing	Reducing
Source	Sugar cane	Barley/malt	Milk

5. Polysaccharides

Definition

Polysaccharides are carbohydrates that produce a large number of monosaccharide units on hydrolysis.

They are polymers of monosaccharides joined through glycosidic linkages.

Characteristics

High molecular mass
Generally tasteless
Insoluble or slightly soluble in water
Used mainly for storage and structural purposes

Examples:

Starch
Cellulose
Glycogen

6. Starch

Introduction

Starch is the main storage polysaccharide of plants.

Sources:

Cereals
Roots
Tubers
Vegetables

It is the most important carbohydrate in the human diet.

Composition of Starch

Starch is made up of:

α-D-glucose units

It has two components:

(A) Amylose

Properties:

Water soluble
About 15–20% of starch
Long unbranched chain

Linkage:

α-D-glucose units joined by:

C-1 → C-4 glycosidic linkage

(B) Amylopectin

Properties:

Insoluble in water
About 80–85% of starch
Branched structure

Linkages:

Main chain:

C-1 → C-4 linkage

Branching:

C-1 → C-6 linkage

7. Cellulose

Introduction

Cellulose is:

The most abundant organic substance in plants
A major component of plant cell walls

Structure

Cellulose is made of:

β-D-glucose units

joined by:

β(1 → 4) glycosidic linkage

Important Point

Humans cannot digest cellulose because our digestive system lacks the enzyme required to break β-glycosidic bonds.

8. Glycogen

Introduction

Glycogen is the storage carbohydrate of animals.

It is also called:

Animal Starch

Location in Body

Glycogen is stored mainly in:

Liver
Muscles
Brain

Structure

Glycogen resembles amylopectin but:

Has more branches
Breaks down to release glucose when required

Starch vs Cellulose vs Glycogen

Feature	Starch	Cellulose	Glycogen
Found in	Plants	Plants	Animals
Function	Energy storage	Structural support	Energy storage
Monomer	α-glucose	β-glucose	α-glucose
Linkage	α(1→4), α(1→6)	β(1→4)	α(1→4), α(1→6)
Branching	Amylopectin branched	No branching	Highly branched

Part 4: Proteins — Amino Acids, Peptide Bonds and Protein Structure

1. Proteins

Introduction

Proteins are among the most important biomolecules present in living organisms.

The word protein comes from the Greek word:

“Proteios”
meaning primary or of prime importance.

Proteins are essential for:

Growth of the body
Repair of tissues
Maintaining body functions
Structural activities
Biological reactions

Sources of Proteins

Important sources include:

Milk
Cheese
Pulses
Peanuts
Fish
Meat

Basic Structure of Proteins

Proteins are polymers of α-amino acids.

This means:

Amino acids are the building blocks.
Many amino acids join together to form proteins.

2. Amino Acids

Definition

Amino acids are organic compounds containing:

Amino group (–NH₂)
Carboxyl group (–COOH)

General structure:

        H
        |
H₂N — C — COOH
        |
        R

Here:

R = side chain

The nature of the R group determines the properties of the amino acid.

Classification of Amino Acids

Amino acids are classified based on:

Number of amino and carboxyl groups
Ability of the body to synthesize them

A. Classification Based on Acidic and Basic Groups

1. Neutral Amino Acids

They contain:

One amino group
One carboxyl group

Example:

Glycine
Alanine

2. Acidic Amino Acids

They contain:

More carboxyl groups than amino groups

Examples:

Aspartic acid
Glutamic acid

3. Basic Amino Acids

They contain:

More amino groups than carboxyl groups

Examples:

Lysine
Arginine

B. Classification Based on Dietary Requirement

1. Essential Amino Acids

Definition:

Amino acids that cannot be synthesized by the human body and must be obtained through diet are called essential amino acids.

Examples:

Valine
Leucine
Lysine
Methionine

2. Non-Essential Amino Acids

Definition:

Amino acids that can be synthesized by the body are called non-essential amino acids.

Examples:

Glycine
Alanine

Important Amino Acids Table

Amino Acid	Symbol
Glycine	Gly
Alanine	Ala
Valine	Val
Leucine	Leu
Lysine	Lys
Glutamic acid	Glu
Aspartic acid	Asp
Serine	Ser
Cysteine	Cys
Methionine	Met
Phenylalanine	Phe
Tyrosine	Tyr
Tryptophan	Trp
Histidine	His
Proline	Pro

3. Zwitter Ion Formation

Amino acids behave differently from ordinary amines and acids.

They exist mainly as dipolar ions in aqueous solution.

This form is called:

Zwitter Ion

Formation

The carboxyl group loses a proton: $-COOH \rightarrow -COO^- + H^+$ −COOH→−COO−+H+

The amino group accepts the proton: $-NH_2 + H^+ \rightarrow -NH_3^+$ −NH2+H+→−NH3+

Therefore, amino acids contain:

Positive charge on amino group
Negative charge on carboxyl group

Properties of Zwitter Ions

Because of zwitterionic nature:

Amino acids behave like salts.
They have high melting points.
They are soluble in water.
They show amphoteric behaviour.

4. Optical Activity of Amino Acids

Most naturally occurring α-amino acids are optically active because their α-carbon is asymmetric.

Exception:

Glycine

Glycine is optically inactive because it has two hydrogen atoms attached to the α-carbon.

Most natural amino acids have:

L-Configuration

5. Peptide Bond / Peptide Linkage

Definition

A peptide bond is an amide linkage formed between:

Carboxyl group (–COOH) of one amino acid
Amino group (–NH₂) of another amino acid

The bond formed is: $-CO-NH-$ −CO−NH−

Formation of Dipeptide

Two amino acids combine with the elimination of water.

Example:

Glycine + Alanine → Glycylalanine + Water

The product contains two amino acids, so it is called a:

Dipeptide

Peptide Chain Classification

Number of Amino Acids	Name
2	Dipeptide
3	Tripeptide
4	Tetrapeptide
5	Pentapeptide
6	Hexapeptide
More than 10	Polypeptide

A polypeptide chain containing more than 100 amino acids and having molecular mass above 10,000 u is generally called a protein.

6. Classification of Proteins Based on Shape

Proteins are mainly of two types:

             Proteins
                |
       ┌────────┴────────┐
       |                 |
 Fibrous proteins   Globular proteins

A. Fibrous Proteins

Structure

Long polypeptide chains arranged parallel to each other.
Stabilised by hydrogen bonds and disulphide bonds.

Properties

Fibre-like structure
Generally insoluble in water

Examples:

Keratin (hair, wool, silk)
Myosin (muscles)

B. Globular Proteins

Structure

Polypeptide chains are folded into spherical shapes.

Properties

Usually soluble in water

Examples:

Insulin
Albumins

7. Levels of Protein Structure

Protein structure exists at four levels:

Primary structure
Secondary structure
Tertiary structure
Quaternary structure

(1) Primary Structure

Definition:

The specific sequence of amino acids in a protein chain is called its primary structure.

Example:

Amino acid sequence:

A → B → C → D

Any change in this sequence produces a different protein.

(2) Secondary Structure

It refers to the regular folding of the polypeptide chain.

Main types:

A. α-Helix

Polypeptide chain twists into a right-handed spiral.
Stabilised by hydrogen bonding.

B. β-Pleated Sheet

Polypeptide chains are stretched and arranged side by side.
Stabilised by hydrogen bonds.

(3) Tertiary Structure

Definition:

The overall three-dimensional folding of a polypeptide chain is called tertiary structure.

It determines the final shape of the protein.

Stabilising Forces:

Hydrogen bonds
Disulphide bonds
Van der Waals forces
Electrostatic attraction

(4) Quaternary Structure

Some proteins contain two or more polypeptide chains called subunits.

The arrangement of these subunits is called:

Quaternary Structure

Example:

Haemoglobin

8. Denaturation of Proteins

Definition

Loss of biological activity of a protein due to changes in temperature or pH is called:

Denaturation

Causes

Physical changes:

High temperature

Chemical changes:

Change in pH

Effect

During denaturation:

Destroyed:

✔ Secondary structure
✔ Tertiary structure

Not destroyed:

✔ Primary structure

Examples

1. Boiling of Egg

Egg white protein coagulates due to denaturation.

2. Curd Formation

Milk protein changes due to lactic acid produced by bacteria.

Important Differences

Fibrous vs Globular Proteins

Fibrous Proteins	Globular Proteins
Fibre-like shape	Spherical shape
Usually insoluble	Usually soluble
Structural function	Functional role
Example: Keratin	Example: Insulin

Protein Structure Quick Revision

Amino acids
      ↓
Peptide bonds
      ↓
Polypeptide chain
      ↓
Protein structure

Primary
   ↓
Secondary
   ↓
Tertiary
   ↓
Quaternary

Part 5: Enzymes and Vitamins

1. Enzymes

Introduction

Living organisms perform thousands of chemical reactions continuously. These reactions occur under mild conditions inside the body with the help of special biological catalysts called:

Enzymes

Most enzymes are:

Globular proteins

They increase the rate of biochemical reactions without being consumed.

Characteristics of Enzymes

1. Biological Catalysts

Enzymes act as catalysts in living systems.

They:

Increase reaction speed
Remain unchanged after reaction
Are required in very small amounts

2. High Specificity

Enzymes are highly specific.

This means:

A particular enzyme works on a particular substrate.
It usually catalyses a particular reaction.

Example:

Maltase

It catalyses: $\text{Maltose} \rightarrow \text{Glucose}$ Maltose→Glucose

3. Enzyme Naming

Most enzymes are named by adding:

“-ase”

to the name of the substrate.

Examples:

Enzyme	Substrate	Reaction
Maltase	Maltose	Maltose → Glucose
Sucrase	Sucrose	Sucrose → Glucose + Fructose

Some enzymes are named according to the reaction they catalyse.

Example:

Oxidoreductases

These enzymes carry out oxidation-reduction reactions.

2. Enzymes and Activation Energy

Activation Energy

Activation energy is the minimum energy required for a chemical reaction to occur.

Enzymes increase reaction rate by:

Reducing activation energy

They provide an easier pathway for the reaction.

Example

Hydrolysis of sucrose:

Without enzyme:

Activation energy = 6.22 kJ mol⁻¹

With enzyme sucrase:

Activation energy = 2.15 kJ mol⁻¹

Thus, enzymes make reactions faster by lowering the energy barrier.

3. Mechanism of Enzyme Action

Enzyme action can be explained by the formation of an:

Enzyme-Substrate Complex

General steps:

Enzyme + Substrate
          ↓
Enzyme-Substrate Complex
          ↓
Product + Enzyme

Important Terms

Substrate

The molecule on which an enzyme acts is called the substrate.

Active Site

The specific region of enzyme where substrate binds is called the active site.

4. Vitamins

Introduction

Vitamins are organic compounds required in:

Very small quantities
Normal growth
Proper functioning of the body

Their deficiency causes specific diseases.

Most vitamins cannot be synthesized by humans and must be obtained through diet.

Origin of the Term “Vitamin”

The word vitamin originated from:

Vital + Amine

Initially, scientists believed vitamins contained amino groups.

Later it was found that most vitamins do not contain amino groups.

Therefore, the letter “e” was removed and the term became:

Vitamin

Classification of Vitamins

Vitamins are classified according to their solubility.

                 Vitamins
                     |
        ┌────────────┴────────────┐
        |                         |
 Fat-soluble vitamins     Water-soluble vitamins
        |                         |
     A, D, E, K              B-group and C

1. Fat-Soluble Vitamins

Definition

Vitamins soluble in fats and oils but insoluble in water are called fat-soluble vitamins.

Examples:

Vitamin A
Vitamin D
Vitamin E
Vitamin K

Storage

They are stored in:

Liver
Fat tissues (adipose tissue)

2. Water-Soluble Vitamins

Definition

Vitamins soluble in water are called water-soluble vitamins.

Examples:

Vitamin B group
Vitamin C

Important Point

They cannot be stored in the body because they are easily removed through urine.

Exception:

Vitamin B₁₂ can be stored.

Important Vitamins, Sources and Deficiency Diseases

Vitamin	Chemical Name	Sources	Deficiency Disease
Vitamin A	Retinol	Fish liver oil, carrots, milk, butter	Night blindness, xerophthalmia
Vitamin B₁	Thiamine	Yeast, cereals, milk	Beriberi
Vitamin B₂	Riboflavin	Milk, eggs, green vegetables	Cheilosis
Vitamin B₆	Pyridoxine	Cereals, meat, fish	Convulsions
Vitamin B₁₂	Cobalamin	Meat, fish, eggs, curd	Pernicious anaemia
Vitamin C	Ascorbic acid	Citrus fruits, amla, green vegetables	Scurvy
Vitamin D	Calciferol	Sunlight, fish, egg yolk	Rickets, osteomalacia
Vitamin E	Tocopherol	Vegetable oils	Muscle weakness, RBC fragility
Vitamin K	—	Green leafy vegetables	Increased blood clotting time

Vitamin Deficiency Diseases — Memory Tricks

Vitamin A → “A for Eyes”

Deficiency:

➡ Night blindness

Vitamin B₁ → “Beri Beri”

Deficiency:

➡ Beriberi

Vitamin C → “C for Citrus”

Deficiency:

➡ Scurvy

Vitamin D → “D for Dense Bones”

Deficiency:

➡ Rickets

Vitamin K → “K for Koagulation”

Deficiency:

➡ Increased blood clotting time

Fat-Soluble vs Water-Soluble Vitamins

Fat-Soluble	Water-Soluble
A, D, E, K	B group, C
Stored in body	Mostly not stored
Stored in liver and fat tissues	Excreted in urine
Excess may accumulate	Regular supply needed

Part 6: Nucleic Acids — DNA, RNA and Their Functions

1. Nucleic Acids

Introduction

Nucleic acids are one of the most important biomolecules present in living organisms.

They are responsible for:

Storage of genetic information
Transfer of genetic information
Protein synthesis

The two major types of nucleic acids are:

DNA (Deoxyribonucleic Acid)
RNA (Ribonucleic Acid)

2. Chemical Composition of Nucleic Acids

Nucleic acids are polymers made up of smaller units called:

Nucleotides

A large number of nucleotides join together to form:

Structure of a Nucleotide

A nucleotide consists of three components:

1. Nitrogenous Base

It may be:

Purine
Pyrimidine

2. Pentose Sugar

It may be:

Ribose (in RNA)
Deoxyribose (in DNA)

3. Phosphoric Acid

It provides the phosphate group.

General Structure

        Nitrogenous Base
              |
              |
          Pentose Sugar
              |
              |
        Phosphate Group

3. Nucleosides

Definition

A compound containing:

Nitrogenous base
Pentose sugar

but without phosphate group is called a:

Nucleoside

Formation

Nitrogenous base + Sugar → Nucleoside

Nucleoside + Phosphoric acid → Nucleotide

Difference Between Nucleoside and Nucleotide

Nucleoside	Nucleotide
Base + Sugar	Base + Sugar + Phosphate
No phosphate group	Contains phosphate group
Forms part of nucleotides	Building unit of DNA/RNA

4. Nitrogenous Bases

Nitrogenous bases are of two types:

             Nitrogenous Bases
                    |
        ┌───────────┴───────────┐
        |                       |
     Purines              Pyrimidines

A. Purine Bases

Purines contain two fused rings.

Examples:

Adenine (A)
Guanine (G)

B. Pyrimidine Bases

Pyrimidines contain one ring.

Examples:

Cytosine (C)
Thymine (T)
Uracil (U)

Bases Present in DNA and RNA

Base	DNA	RNA
Adenine (A)	✓	✓
Guanine (G)	✓	✓
Cytosine (C)	✓	✓
Thymine (T)	✓	✗
Uracil (U)	✗	✓

5. DNA (Deoxyribonucleic Acid)

Introduction

DNA is the molecule responsible for storing hereditary information.

It controls:

Growth
Development
Reproduction
Characteristics of organisms

DNA is present mainly in:

Cell nucleus

Sugar Present in DNA

DNA contains:

Deoxyribose sugar

The absence of one oxygen atom compared with ribose gives DNA its name:

Deoxyribonucleic acid

6. Structure of DNA

The structure of DNA was proposed by:

Watson and Crick (1953)

They suggested the:

Double Helical Structure

Features of DNA Double Helix

1. Two Polypeptide-like Chains

DNA consists of two long nucleotide chains.

These chains are arranged:

Opposite to each other
In a helical manner

2. Sugar-Phosphate Backbone

The outer part of DNA contains:

Sugar molecules
Phosphate groups

These form the backbone of DNA.

3. Base Pairing

Nitrogen bases form pairs through hydrogen bonds.

Rules of base pairing:

Adenine pairs with Thymine

$A = T$ A=T

(two hydrogen bonds)

Guanine pairs with Cytosine

$G \equiv C$ G≡C

(three hydrogen bonds)

4. Complementary Strands

The two strands of DNA are complementary.

This means:

If one strand contains:

A → T
G → C

the other strand will contain:

T → A
C → G

Importance of Complementary Base Pairing

It allows:

Accurate copying of DNA
Transfer of genetic information from one generation to another

7. RNA (Ribonucleic Acid)

Introduction

RNA is another important nucleic acid.

It plays a major role in:

Protein synthesis
Transfer of genetic information

Differences Between DNA and RNA

DNA	RNA
Contains deoxyribose sugar	Contains ribose sugar
Usually double-stranded	Usually single-stranded
Contains thymine	Contains uracil
Stores genetic information	Helps in protein synthesis

Types of RNA

There are three main types:

                RNA
                 |
     ┌───────────┼───────────┐
     |           |           |
   mRNA        tRNA        rRNA

1. Messenger RNA (mRNA)

Function:

Carries genetic information from DNA to ribosomes.

It acts as a template for protein formation.

2. Transfer RNA (tRNA)

Function:

Carries amino acids to ribosomes during protein synthesis.

It helps arrange amino acids in the correct sequence.

3. Ribosomal RNA (rRNA)

Function:

It forms a major part of ribosomes.

Ribosomes are the sites where proteins are synthesized.

DNA vs RNA — Quick Comparison

Feature	DNA	RNA
Full form	Deoxyribonucleic acid	Ribonucleic acid
Sugar	Deoxyribose	Ribose
Strands	Double	Usually single
Base	Thymine present	Uracil present
Main role	Genetic storage	Protein synthesis

8. Biological Functions of Nucleic Acids

DNA Functions

1. Storage of Genetic Information

DNA stores hereditary information.

2. Transmission of Hereditary Characters

DNA passes information from parents to offspring.

3. Controls Protein Formation

DNA contains instructions for making proteins.

RNA Functions

1. Protein Synthesis

RNA helps in converting genetic information into proteins.

2. Transport of Amino Acids

tRNA carries amino acids during protein formation.

9. DNA Fingerprinting

Introduction

DNA fingerprinting is a technique used to identify individuals based on differences in DNA sequences.

It is useful in:

Crime investigations
Establishing biological relationships
Identification of individuals

Revision

Nucleic Acids
       |
 ┌─────┴─────┐
 DNA         RNA
 |            |
Genetic     Protein
storage     synthesis

Nucleotide =
Base + Sugar + Phosphate

Nucleoside =
Base + Sugar

Part 7: Hormones + Complete Chapter Revision

1. Hormones

Introduction

Hormones are chemical substances produced by endocrine glands that control and regulate various activities of the body.

They act as:

Chemical messengers
Regulators of physiological processes

Hormones are transported through blood to specific target organs where they produce their effects.

Classification of Hormones

Hormones can be broadly classified into:

                Hormones
                    |
       ┌────────────┴────────────┐
       |                         |
   Peptide Hormones        Steroid Hormones

1. Peptide Hormones

Definition

Peptide hormones are made up of amino acid chains.

Examples:

Insulin
Oxytocin
Vasopressin

Insulin

Source:

Produced by:

Pancreas

Function:

Controls blood glucose level
Helps cells absorb glucose from blood

Importance:

Insufficient insulin production causes:

Diabetes mellitus

2. Steroid Hormones

Definition

Steroid hormones are derived from cholesterol and contain steroid structures.

Examples:

Sex hormones
Adrenal hormones

Sex Hormones

Male Sex Hormone:

Testosterone

Function:

Development of male reproductive organs
Development of secondary sexual characteristics

Female Sex Hormones:

Estrogen and Progesterone

Functions:

Development of female reproductive system
Regulation of reproductive cycle

Protein Hormones vs Steroid Hormones

Protein Hormones	Steroid Hormones
Made of amino acids	Derived from cholesterol
Water soluble	Lipid soluble
Example: Insulin	Example: Testosterone

COMPLETE CHAPTER REVISION

Biomolecules — One Shot Summary

1. Carbohydrates

Definition

Carbohydrates are polyhydroxy aldehydes, polyhydroxy ketones, or substances that produce them on hydrolysis.

Classification

Carbohydrates

Monosaccharides
       |
Glucose, Fructose

Disaccharides
       |
Sucrose, Maltose, Lactose

Polysaccharides
       |
Starch, Cellulose, Glycogen

Important Facts

Glucose

Aldohexose
Formula: C₆H₁₂O₆
Exists in α and β forms
Forms pyranose ring

Fructose

Ketohexose
Fruit sugar
Forms furanose ring

Important Disaccharides

Compound	Components	Nature
Sucrose	Glucose + Fructose	Non-reducing
Maltose	Glucose + Glucose	Reducing
Lactose	Galactose + Glucose	Reducing

Important Polysaccharides

Polysaccharide	Function
Starch	Plant storage carbohydrate
Glycogen	Animal storage carbohydrate
Cellulose	Plant structural material

2. Proteins

Basic Unit:

Amino acids

General structure:

      H
      |
H₂N — C — COOH
      |
      R

Peptide Bond

The bond between two amino acids: $-CO-NH-$ −CO−NH−

is called peptide linkage.

Protein Structure Levels

Primary Structure

Sequence of amino acids.

Secondary Structure

α-helix
β-pleated sheet

Tertiary Structure

Three-dimensional folding.

Quaternary Structure

Arrangement of multiple chains.

Protein Classification

Fibrous Proteins

Long chain structure
Insoluble
Example: Keratin

Globular Proteins

Spherical shape
Usually soluble
Example: Insulin

Denaturation

Loss of biological activity of protein due to:

Temperature change
pH change

Primary structure remains unchanged.

3. Enzymes

Definition

Enzymes are biological catalysts that increase the rate of biochemical reactions.

Properties

Mostly proteins
Highly specific
Reduce activation energy
Work under mild conditions

Enzyme Action

Enzyme + Substrate
        ↓
Enzyme-Substrate Complex
        ↓
Product + Enzyme

4. Vitamins

Classification

Vitamins

Fat Soluble:
A, D, E, K

Water Soluble:
B-group, C

Important Deficiency Diseases

Vitamin	Deficiency
A	Night blindness
B₁	Beriberi
B₁₂	Pernicious anaemia
C	Scurvy
D	Rickets
K	Increased clotting time

5. Nucleic Acids

Types

Nucleotide

Contains:

Nitrogenous base
Sugar
Phosphate group

Nucleoside

Contains:

Nitrogenous base
Sugar

(No phosphate)

DNA

Function:

Stores genetic information
Transfers hereditary characters

Base Pairing:

A = T

G ≡ C

RNA

Types:

RNA Type	Function
mRNA	Carries genetic message
tRNA	Transfers amino acids
rRNA	Forms ribosomes

Important Differences for Exams

DNA vs RNA

DNA	RNA
Deoxyribose sugar	Ribose sugar
Double stranded	Usually single stranded
Thymine present	Uracil present
Genetic storage	Protein synthesis

Final Biomolecules Mind Map

                 BIOMOLECULES

                      |
 ------------------------------------------------
 |              |              |                |
Carbohydrates Proteins     Nucleic Acids    Vitamins
 |              |              |                |
Sugars       Amino acids      DNA/RNA        A,D,E,K
 |              |                               B,C
Energy       Peptide bonds
Storage      Protein structure