Adenine + ribose + three phosphates

Adenine + deoxyribose + three phosphates

Guanine + ribose + two phosphates

The Molecules of Life

📚

MOLECULES IN LIFE

▢ Basic Idea:

❖ Definition: Biomolecules = chemical substances in living organisms → structure + energy + genetic information + biochemical control

❖ Focus:

•
Carbohydrates
•
Proteins
•
Lipids
•
Nucleic acids
•
Enzymes
•
Vitamins
•
Hormones
•
Water
•
Minerals

Table 1: Major Bioelements

Element	Importance
C	Backbone of organic molecules
H, O	Water, carbohydrates, lipids
N	Proteins, nucleic acids
P	ATP, DNA, RNA, phospholipids
S	Sulphur amino acids, disulfide bonds

❖ Carbon Property: Catenation → chains + branches + rings → carbon-based life

▢ Important Bonds:

Table 1: Bonds in Biomolecules

Bond	Found in	Formed between
Glycosidic bond	Carbohydrates	Two monosaccharides
Peptide bond	Proteins	Two amino acids
Ester bond	Lipids	Fatty acid + glycerol
Phosphodiester bond	DNA / RNA	Sugar + phosphate
Hydrogen bond	DNA, proteins, water	Weak attraction
Disulfide bond	Proteins	Two cysteine amino acids

❖ Condensation: Small molecules join by removal of H2O

❖ Hydrolysis: Biomolecule breakdown by addition of H2O

▢ Carbohydrates:

❖ Definition: Polyhydroxy aldehydes / ketones or substances giving them on hydrolysis

❖ General Formula: Cx(H2O)y

❖ Example: Glucose = C6H12O6

❖ Monosaccharides:

◉ Definition: Simplest carbohydrates; cannot be hydrolysed further

Table 1: Important Monosaccharides

Monosaccharide	Type
Glucose	Aldohexose
Fructose	Ketohexose
Galactose	Aldohexose
Ribose	Aldopentose
Deoxyribose	Pentose sugar of DNA

◉ Aldose: Contains aldehyde group

◉ Ketose: Contains ketone group

◉ Glucose: Dextrose → dextrorotatory

◉ Fructose: Levulose → strongly laevorotatory

❖ Disaccharides:

◉ Definition: Two monosaccharides joined by condensation

Table 1: Disaccharides

Disaccharide	Components	Nature
Maltose	Glucose + glucose	Reducing
Lactose	Glucose + galactose	Reducing
Sucrose	Glucose + fructose	Non-reducing

◉ Trap: Sucrose non-reducing → both anomeric carbons involved in glycosidic bond

❖ Polysaccharides:

◉ Definition: Polymers of monosaccharides

Table 1: Polysaccharides

Polysaccharide	Function
Starch	Storage carbohydrate in plants
Glycogen	Storage carbohydrate in animals
Cellulose	Structural carbohydrate in plants
Chitin	Arthropod exoskeleton + fungal cell wall

◉ Iodine Test:

•
Starch → blue-black
•
Glycogen → reddish-brown

◉ Cellulose: Not digested by humans due to absence of cellulase

❖ Reducing Sugars:

◉ Definition: Sugars reducing Fehling / Benedict reagent due to free aldehyde or ketone group

Table 1: Reducing vs Non-reducing Sugars

Reducing sugars	Non-reducing sugar
Glucose	Sucrose
Fructose
Maltose
Lactose

◉ Important: Fructose = ketose but reducing due to aldose isomerisation in alkaline medium

▢ Proteins:

❖ Definition: Polymers of amino acids joined by peptide bonds

❖ Amino Acid: NH2-CH(R)-COOH

❖ Functional Groups:

•
Amino group = -NH2
•
Carboxyl group = -COOH
•
R group → amino acid type

❖ Peptide Bond: -COOH + -NH2 → -CONH- + H2O

Table 1: Protein Classification by Composition

Type	Description	Example
Simple protein	Only amino acids on hydrolysis	Albumin
Conjugated protein	Protein + non-protein part	Hemoglobin
Derived protein	Partial hydrolysis product	Peptones

Table 2: Protein Classification by Shape

Type	Nature	Example
Fibrous protein	Long, insoluble, structural	Keratin, collagen
Globular protein	Spherical, soluble, functional	Enzymes, hemoglobin

Table 3: Protein Structure Levels

Level	Meaning	Bond
Primary	Amino acid sequence	Peptide bond
Secondary	α-helix / β-pleated sheet	Hydrogen bond
Tertiary	3D folding of one chain	H-bond, ionic bond, disulfide bond
Quaternary	Many polypeptide chains	Weak bonds

❖ Hemoglobin: Quaternary structure → 4 polypeptide chains

❖ Denaturation:

◉ Definition: Loss of natural structure + biological activity

◉ Causes:

•
Heat
•
Strong acid / base
•
Heavy metals: Hg2+, Pb2+
•
Alcohol

◉ Important: Primary structure usually intact; secondary and tertiary structures destroyed

◉ Trap: Denaturation does not easily break peptide bonds

▢ Enzymes:

❖ Definition: Biological catalysts; mostly proteins

❖ Function: Increase reaction rate by lowering activation energy

Table 1: Enzyme Properties

Property	Explanation
Specific	One enzyme acts on specific substrate
Efficient	Small amount works rapidly
Optimum temperature	Usually around 37°C in humans
Optimum pH	Different for different enzymes
Not consumed	Remain unchanged after reaction

❖ Lock and Key Model: Enzyme active site fits only specific substrate

❖ Reaction: Enzyme + substrate → enzyme-substrate complex → product + enzyme

❖ Examples:

•
Sucrase → sucrose
•
Urease → urea

❖ Factors Affecting Activity:

Table 1: Factors

Factor	Effect
Temperature	Activity ↑ up to optimum; then ↓ due to denaturation
pH	Each enzyme has optimum pH
Substrate concentration	Activity ↑ up to saturation
Inhibitors	Decrease enzyme activity
Activators / cofactors	Increase enzyme activity

❖ Inhibition:

Table 1: Enzyme Inhibition

Type	Meaning
Competitive inhibition	Inhibitor resembles substrate; competes for active site
Non-competitive inhibition	Inhibitor binds away from active site; changes enzyme shape

◉ Example: Malonate competitively inhibits succinate dehydrogenase

▢ Lipids:

❖ Definition: Water-insoluble biomolecules soluble in organic solvents like ether, chloroform, benzene

❖ Examples:

•
Fats
•
Oils
•
Waxes
•
Phospholipids
•
Steroids

❖ Simple Lipids: Fats and oils = esters of glycerol + fatty acids

❖ Reaction: Glycerol + fatty acids → triglyceride + water

❖ Bond: Ester bond

Table 1: Fatty Acids

Type	Feature	Example
Saturated fatty acid	No double bond	Palmitic acid, stearic acid
Unsaturated fatty acid	One or more double bonds	Oleic acid, linoleic acid

Table 2: Important Lipids

Lipid	Function
Triglycerides	Energy storage
Phospholipids	Cell membrane
Cholesterol	Steroid hormone precursor
Waxes	Protective coating
Steroids	Hormones, vitamin D, bile salts

Table 3: Energy Value

Molecule	Energy
Carbohydrate	4 kcal/g
Protein	4 kcal/g
Fat	9 kcal/g

❖ Fats: Usually solid at room temperature; mostly saturated fatty acids

❖ Oils: Usually liquid at room temperature; mostly unsaturated fatty acids

❖ Competitive Point: Lipids give maximum energy per gram

▢ Nucleic Acids:

❖ Definition: Polymers of nucleotides

Table 1: DNA vs RNA

Feature	DNA	RNA
Full form	Deoxyribonucleic acid	Ribonucleic acid
Sugar	Deoxyribose	Ribose
Bases	A, G, C, T	A, G, C, U
Structure	Double-stranded	Mostly single-stranded
Location	Nucleus, mitochondria	Nucleus, cytoplasm
Function	Genetic storage	Protein synthesis

❖ Nucleotide Components:

Nitrogenous base
Pentose sugar
Phosphate group

❖ Nucleoside: Base + sugar

❖ Nucleotide: Base + sugar + phosphate

❖ Nitrogenous Bases:

Table 1: Purines and Pyrimidines

Purines	Pyrimidines
Adenine	Cytosine
Guanine	Thymine
	Uracil

◉ Purines: Two rings

◉ Pyrimidines: One ring

◉ Mnemonic: Pure As Gold → Purines = Adenine + Guanine

❖ Base Pairing:

•
A-T → 2 hydrogen bonds
•
G-C → 3 hydrogen bonds
•
G-C rich DNA → more stable

❖ RNA Types:

Table 1: RNA Types

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

▢ ATP:

❖ Full Form: Adenosine triphosphate

❖ Composition: Adenine + ribose + three phosphate groups

❖ Breakdown: ATP → ADP + Pi + energy

❖ Name: Energy currency of cell

❖ Reason: Energy stored in high-energy phosphate bonds

▢ Vitamins:

❖ Definition: Organic compounds required in small amounts for normal metabolism

❖ Energy: Do not provide energy

❖ Role: Help biochemical reactions

❖ Fat Soluble:

◉ Mnemonic: ADEK

Table 1: Fat-soluble Vitamins

Vitamin	Function	Deficiency
A	Vision, epithelial health	Night blindness
D	Calcium absorption, bone health	Rickets, osteomalacia
E	Antioxidant	Sterility, hemolysis
K	Blood clotting	Bleeding tendency

❖ Water Soluble:

Table 1: Water-soluble Vitamins

Vitamin	Deficiency
B1	Beriberi
B2	Cheilosis, glossitis
B3	Pellagra
B6	Convulsions, neuropathy
B12	Pernicious anemia
C	Scurvy

◉ Vitamin C: Needed for collagen synthesis

◉ Vitamin C Deficiency: Bleeding gums + poor wound healing

▢ Hormones:

❖ Definition: Chemical messengers secreted by endocrine glands

❖ Functions:

•
Growth
•
Metabolism
•
Reproduction
•
Homeostasis

Table 1: Chemical Nature of Hormones

Type	Examples	Receptor
Peptide hormone	Insulin, glucagon	Cell surface receptor
Steroid hormone	Cortisol, testosterone, estrogen	Intracellular receptor
Amino acid derivative	Thyroxine, adrenaline	Variable

❖ Steroid Hormones: Lipid-soluble → pass through cell membrane

❖ Peptide Hormones: Water-soluble → bind cell surface receptors

▢ Water:

❖ Definition: Most abundant molecule in living organisms

❖ Name: Universal solvent

❖ Reason: Many ionic and polar substances dissolve in it

Table 1: Properties of Water

Property	Biological importance
Polar nature	Good solvent
Hydrogen bonding	High boiling point, cohesion
High specific heat	Maintains body temperature
High heat of vaporization	Cooling by sweating
Participates in reactions	Hydrolysis, condensation

▢ Minerals:

❖ Definition: Inorganic elements required for body functions

Table 1: Important Minerals

Mineral	Function
Calcium	Bones, teeth, blood clotting
Phosphorus	ATP, DNA, bones
Iron	Hemoglobin
Iodine	Thyroxine
Sodium	Nerve impulse, fluid balance
Potassium	Nerve and muscle function
Magnesium	Enzyme cofactor

▢ Important Chemical Tests:

Table 1: Biomolecule Tests

Test	Detects	Positive result
Molisch test	Carbohydrates	Violet ring
Benedict test	Reducing sugar	Brick-red precipitate
Fehling test	Reducing sugar	Red precipitate
Iodine test	Starch	Blue-black colour
Biuret test	Protein	Violet colour
Ninhydrin test	Amino acids	Purple colour
Sudan III test	Lipids	Red/orange stain

▢ High-Yield Competitive Points:

Table 1: Must Remember

Clue	Answer
Glucose	Aldohexose
Fructose	Ketohexose
Non-reducing sugar	Sucrose
Reducing disaccharides	Maltose, lactose
Plant storage carbohydrate	Starch
Animal storage carbohydrate	Glycogen
Plant structural polysaccharide	Cellulose
Arthropod / fungal structural polysaccharide	Chitin
Protein bond	Peptide bond
Carbohydrate bond	Glycosidic bond
Fat bond	Ester bond
DNA/RNA backbone bond	Phosphodiester bond
A-T bonds	2 hydrogen bonds
G-C bonds	3 hydrogen bonds
DNA base absent in RNA	Thymine
RNA base absent in DNA	Uracil
Nucleoside	Lacks phosphate
Nucleotide	Contains phosphate
Enzymes	Mostly proteins
Energy currency	ATP
Blood clotting vitamin	Vitamin K
Calcium absorption vitamin	Vitamin D
Scurvy	Vitamin C deficiency
Beriberi	Vitamin B1 deficiency
Pellagra	Vitamin B3 deficiency
Maximum energy per gram	Lipids

▢ Common MCQ Traps:

Table 1: Traps

Question style	Correct answer
Non-reducing sugar	Sucrose
Storage carbohydrate in animals	Glycogen
Structural carbohydrate in plants	Cellulose
Bond in protein	Peptide bond
Bond in DNA backbone	Phosphodiester bond
Base absent in DNA	Uracil
Base absent in RNA	Thymine
Energy currency	ATP
Fat-soluble vitamins	A, D, E, K
Universal solvent	Water
Protein test	Biuret test
Starch test	Iodine test

▢ Final Summary:

Table 1: Biomolecule Quick Role

Biomolecule	Role
Carbohydrates	Energy + structure
Proteins	Body building + enzymes + transport
Lipids	Energy storage + membrane
Nucleic acids	Genetic information
ATP	Energy currency
Vitamins	Coenzymes + regulation
Water	Solvent + reaction medium
Minerals	Structural + functional ions

Q1.

Which of the following is a non-reducing disaccharide?

Q2.

Fructose gives positive Benedict’s test because

Q3.

The blue-black colour of starch with iodine is mainly due to

Q4.

Humans cannot digest cellulose because

Q5.

Which polysaccharide is most highly branched?

Q6.

Which pair contains only reducing sugars?

Q7.

The monomer of protein is

Q8.

A peptide bond is formed between

Q9.

During protein denaturation, which structure usually remains unchanged?

Q10.

α-helix of protein is stabilized mainly by

Q11.

Which protein has quaternary structure?

Q12.

Biuret test detects

Q13.

Ninhydrin test is used for detection of

Q14.

Enzymes increase the rate of reaction by

Q15.

Competitive inhibition can be overcome by increasing

Q16.

Malonate inhibits succinate dehydrogenase because malonate

Q17.

Which statement about enzymes is incorrect?

Q18.

The optimum temperature for most human enzymes is around

Q19.

Lipids are soluble in

Q20.

Fats are esters of

Q21.

The bond present in triglyceride is

Q22.

Which molecule gives maximum energy per gram?

Q23.

Phospholipids are important because they

Q24.

The amphipathic nature of phospholipid means

Q25.

Cholesterol is a precursor of

Q26.

Nucleic acids are polymers of

Q27.

A nucleoside contains

Q28.

A nucleotide contains

Q29.

The bond present in DNA backbone is

Q30.

In DNA, adenine pairs with thymine by

Q31.

GC-rich DNA is more stable because

Q32.

Which base is absent in DNA?

Q33.

Which base is absent in RNA?

Q34.

Purines are

Q35.

Pyrimidines present in DNA are

Q36.

ATP is made up of

Q37.

ATP releases energy mainly when

Q38.

Which vitamin is fat-soluble?

Q39.

Vitamin K is required for

Q40.

Vitamin C deficiency causes

Q41.

Pellagra is due to deficiency of

Q42.

Beriberi is caused by deficiency of

Q43.

Rickets occurs due to deficiency of

Q44.

Night blindness occurs due to deficiency of

Q45.

Water has high specific heat because of

Q46.

Water is a good solvent because it is

Q47.

Iron is essential for formation of

Q48.

Iodine is required for synthesis of

Q49.

Calcium is important for all except

Q50.

The correct matching is

46The Molecules of Life