Chapter 2 Biological Molecules Class 11 Notes are essentially design to Quickly revise Major topics before exam including important topics like the structure and functions of carbohydrates, proteins, lipids, nucleic acids, and enzymes. The notes makes complex ideas easy-to-understand with clear explanations, summaries, and key facts that help students quickly learn and remember the material.
2.1 BIOLOGICAL MOLECULES IN PROTOPLASM
🔹 Bio-molecules = Chem. compounds in 🏽 living org.
🔹 Biochemistry = Study of bio-molecules + metabolism
2.1.1 Chem. Composition of Protoplasm
✔ Bioelements (25/92 natural elements found in life)
✔ Human body = 16 bioelements
Bioelements Classification:
- Major (99%): O (65%), C (18%), H (10%), N (3%), Ca (2%), P (1%)
- Minor (<1%): K (0.35%), S (0.25%), Cl (0.15%), Na (0.15%), Mg (0.05%)
- Trace (<0.01%): Fe, Cu, Mn, Zn
Bioelements form Biomolecules:
- Inorganic → 💧 H₂O, minerals
- Organic → 🥖 Carbs, 🏋 Proteins, 🛢️ Lipids, 🧬 Nucleic Acids
2.1.2 Proportions of Biomolecules in Cells
| Biomolecule | Bacterial Cell (%) | Mammalian Cell (%) |
|---|---|---|
| H₂O | 70% | 70% |
| Proteins | 15% | 18% |
| Carbs | 3% | 4% |
| Lipids | 2% | 3% |
| DNA | 1% | 0.25% |
| RNA | 6% | 1.1% |
| Other Org. Mol. | 2% | 2% |
| Inorganic Ions | 1% | 1% |
Bio-molecule Functions:
- Carbs → 🏽 Energy (Cytoplasm)
- Proteins → 🏗️ Structure (Membranes, Ribosomes, Enzymes)
- Lipids → 🛢️ Reserve Energy (Membranes, Cytoplasm)
- DNA → 🧬 Genetic Control (Chromosomes)
- RNA → 📩 Genetic Messenger (Nucleoplasm, Cytoplasm)
2.1.3 Condensation & Hydrolysis
✔ Macromolecules = High MW compounds, polymers of monomers
✔ Monomers = Small units forming polymers
Condensation (Dehydration Synthesis)
- 2 monomers join, -OH (1st) + -H (2nd) → H₂O removed
- New bond forms → Dimer
- Repeated reaction → Polymer
- Needs enzymes + energy
Hydrolysis (Reverse of Condensation)
- H₂O added → Breaks bond b/w monomers
- H attaches (1st monomer), OH attaches (2nd monomer)
- Digestion = Example (enzymes: carbohydrases, proteases, lipases)
🛑 Note: Hydrolysis ≠ Hydration (H₂O as solvent, no bond breaking)
2.2 IMPORTANCE OF WATER
✔ H₂O = Essential for life 🌍
- Covers > ⅔ Earth 🌊
- Body composition ~70%
- Lowest in seeds/bones (20%)
- Highest in brain cells (85-90%)
- Jellyfish = 99% H₂O
2.2.1 Properties of Water
✔ 1. High Polarity
- H₂O = Polar molecule (O⁻, H⁺)
- Dissolves ionic & polar compounds
✔ 2. Hydrogen Bonding
- Weak H-bonds b/w H₂O molecules
- Maintains liquid state
✔ 3. Cohesion & Adhesion
- Cohesion = H₂O-H₂O attraction (surface tension) 🌊
- Adhesion = H₂O attaches to polar surfaces (capillary action) 🌱
✔ 4. High Specific Heat Capacity 🌡️
- Absorbs heat w/ min temp change (1 cal raises 1g H₂O by 1°C)
- Prevents sudden thermal fluctuations
✔ 5. High Heat of Vaporization ☀️💧
- 574 cal/g needed to evaporate → Cools organisms (sweating)
✔ 6. Hydrophobic Exclusion 🚫💧
- Non-polar substances cluster in H₂O (e.g., oil in water)
- Important for lipid bilayer formation
✔ 7. Ionization
- H₂O dissociates → H⁺ + OH⁻
- Regulates pH in cells
✔ 8. Lower Density of Ice 🧊
- Ice < dense than liquid H₂O → Floats
- Insulates aquatic life during freezing temps ❄️🐟
2.3 CARBOHYDRATES
✔ C, H, O compounds → "Hydrates of carbon"
✔ Functions: 🏽 Energy source, 🌱 Structure, 📦 Storage
2.3.1 Classification of Carbs
| Type | Units | Hydrolysis | Solubility | Examples |
|---|---|---|---|---|
| Monosaccharides | 1 | ❌ | ✅ | Glucose, Fructose, Galactose |
| Oligosaccharides | 2-10 | ✅ (2-10 mono) | ☑️ | Maltose, Lactose, Sucrose |
| Polysaccharides | >10 | ✅ (>10 mono) | ❌ | Starch, Glycogen, Cellulose, Chitin |
2.3.2 Monosaccharides
✔ Basic sugar unit
✔ Types based on:
1️⃣ Functional Group
- Aldoses (-CHO) → Glucose
- Ketoses (-CO) → Fructose
2️⃣ C-Number (CnH2nOn)
- Trioses (3C) → Glyceraldehyde
- Tetroses (4C) → Erythrose
- Pentoses (5C) → Ribose, Deoxyribose
- Hexoses (6C) → Glucose, Fructose
- Heptoses (7C) → Sedoheptulose
✔ Structure
- Open-chain → Dry form
- Ring (cyclic) → Aqueous form
- α-Glucose (-OH ↓) vs β-Glucose (-OH ↑)
✔ Stereoisomers
- D & L forms (D = natural, digestible, L = synthetic, undigestible)
2.3.3 Oligosaccharides (Disaccharides)
✔ 2-10 monosaccharides joined by glycosidic bonds
✔ Disaccharides (C₁₂H₂₂O₁₁) → Most common oligosaccharides
| Disaccharide | Monosaccharides | Bond Type | Function |
|---|---|---|---|
| Sucrose (Cane sugar) | Glucose + Fructose | α-1,2-glycosidic | Transport sugar in 🌱 |
| Maltose (Malt sugar) | Glucose + Glucose | α-1,4-glycosidic | 🌾 Starch digestion |
| Lactose (Milk sugar) | Galactose + Glucose | β-1,4-glycosidic | 🥛 Present in milk |
✔ Reducing vs Non-Reducing Sugars
- Reducing → Free -CHO/-CO (Maltose, Lactose)
- Non-Reducing → No free -CHO/-CO (Sucrose)
2.3.4 Polysaccharides
✔ >10 monosaccharides, complex structure
✔ 2 Types:
- Homopolysaccharides → 🔹 Same mono units (Starch, Glycogen, Cellulose, Chitin)
- Heteropolysaccharides → 🔹 Different mono units (Agar, Pectin, Peptidoglycan)
| Polysaccharide | Composition | Function | Structure |
|---|---|---|---|
| Starch | α-Glucose | 🌱 Storage carb | Amylose (Linear) + Amylopectin (Branched) |
| Glycogen | α-Glucose | 🏽 Storage carb (liver/muscles) | Highly branched |
| Cellulose | β-Glucose | 🌱 Cell wall struct. | Linear, unbranched |
| Chitin | N-acetylglucosamine | 🍄🍤 Fungi cell wall + Arthropod exoskeleton | Unbranched |
2.4 PROTEINS
✔ Polymers of amino acids (AAs)
✔ Contain → C, H, O, N (+ some S, P, Fe, I, Mg)
2.4.1 Structure of Proteins
✔ Amino Acid Structure:
- α-Carbon (C) + 4 Groups → H, -NH₂, -COOH, R (Variable)
✔ Peptide Bond Formation:
- Condensation Reaction
- -OH (COOH) + -H (NH₂) → H₂O
- Peptide Bond (-CO-NH-) Forms
- Dipeptide = 2 AAs
- Polypeptide = Many AAs
2.4.2 Levels of Protein Structure
| Level | Description | Example |
|---|---|---|
| Primary | 🔹 AA sequence (linear) | Insulin |
| Secondary | 🔹 H-bonds → α-Helix / β-Pleated Sheet | Keratin, Silk |
| Tertiary | 🔹 3D globular struct. (Ionic, Disulfide Bonds) | Enzymes, Myoglobin |
| Quaternary | 🔹 2+ polypeptides | Hemoglobin, Collagen |
2.4.3 Importance of AA Sequence
✔ Sequence determines function
✔ Mutation → Disease
- Example: Sickle Cell Anemia
- Cause: Mutation in β-Globin (Hb)
- Effect: Glutamic Acid → Valine (Hydrophilic → Hydrophobic)
- Results: 🩸 RBCs → Sickle shape, ↓ O₂ transport
2.4.4 Classification of Proteins
| Type | Shape | Properties | Examples |
|---|---|---|---|
| Fibrous | 🧵 Long, thread-like | Insoluble, Elastic | Collagen (CT), Keratin (Hair, Nails), Myosin (Muscles) |
| Globular | ⚫ Spherical | Soluble, Functional | Enzymes, Hemoglobin, Antibodies, Hormones |
2.4.5 Functions of Proteins
| Type | Function | Example |
|---|---|---|
| Structural | 🏗️ Support & Shape | Collagen (CT), Keratin (Hair, Nails), Elastin (Skin) |
| Enzymatic | ⚡ Speed up reactions | Amylase (Starch), Pepsin (Proteins), DNA Polymerase |
| Transport | 🚚 Carry substances | Hemoglobin (O₂), Albumin (Fats) |
| Defensive | 🛡️ Immunity | Antibodies |
| Regulatory | 🔄 Control processes | Insulin (Glucose), GH (Growth) |
| Contractile | 💪 Movement | Actin & Myosin (Muscles) |
2.5 LIPIDS
✔ Hydrophobic (water-insoluble)
✔ Contain C, H, O (↓O than carbs)
2.5.1 Functions
✔ Structural → Cell membrane (Phospholipids, Cholesterol)
✔ ⚡ Energy Storage → 2× energy of carbs (Triglycerides)
✔ 🛡️ Protection & Insulation → Fat deposits
✔ 💧 Waterproofing → Waxes (Plants, Insects)
✔ 📡 Signaling → Hormones (Steroids)
2.5.2 Types of Lipids
| Type | Composition | Example |
|---|---|---|
| Acylglycerols | Glycerol + Fatty Acids | Triglycerides, Mono/Diacylglycerols |
| Waxes | Fatty Acid + Alcohol | Beeswax, Cutin (Leaf Coating) |
| Phospholipids | Glycerol + 2 FA + Phosphate | Lecithin, Phosphatidylcholine |
| Steroids | 4-Ring Structure | Cholesterol, Testosterone, Estrogen |
| Terpenes | Isoprene Units | Vitamin A, Carotenoids, Rubber |
| Prostaglandins | Fatty Acid Derivative | PGE2 (Inflammation) |
2.5.3 Fatty Acids & Triglycerides
✔ Fatty Acids = Hydrocarbon chain + -COOH
✔ Types:
- Saturated → ❌ No double bonds (🧈 Solid, animal fats)
- Unsaturated → ✅ 1+ double bonds (🥑 Liquid, plant oils)
✔ Triglycerides (Neutral Fats)
- Glycerol + 3 FA
- Stored energy (Adipose Tissue)
2.6 NUCLEIC ACIDS
✔ Genetic material 🧬 → Stores & transfers info
✔ Discovered → 1869 by F. Miescher ("Nuclein")
2.6.1 Types of Nucleic Acids
1️⃣ DNA (Deoxyribonucleic Acid) → Genetic storage
2️⃣ RNA (Ribonucleic Acid) → Protein synthesis
2.6.2 Structure of Nucleic Acids
✔ Nucleotide = Basic Unit
🔹 Components:
- Pentose Sugar → Ribose (RNA) / Deoxyribose (DNA)
- Nitrogenous Base →
- Purines (A, G)
- Pyrimidines (C, T in DNA, U in RNA)
- Phosphate Group → (-ve charge, acidic)
✔ Comparison:
| Component | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C |
| Strands | Double-stranded | Single-stranded |
2.6.3 Watson & Crick DNA Model
✔ Proposed in 1953 🏆
✔ Based on:
- Chargaff’s Rule (A=T, G=C)
- X-ray diffraction (Franklin & Wilkins)
✔ Structure:
- 2 antiparallel strands (5’→3’ & 3’→5’)
- H-bonding
- A=T (2 H-bonds)
- G≡C (3 H-bonds)
- Double Helix → 2 nm wide, 10 bp/turn
2.6.4 Concept of Gene
✔ Gene = DNA segment coding for a protein
✔ Carries genetic instructions (codons = 3 bases = 1 AA)
✔ Central Dogma → DNA → RNA → Protein
✔ Mutation (🔄 sequence change) → Genetic disorders
2.6.5 Types of RNA
✔ RNA = Single-stranded 📜, involved in protein synthesis
✔ 3 Major Types:
| Type | Function | Structure |
|---|---|---|
| mRNA (Messenger RNA) | 📡 Carries genetic code 🧬 from DNA → Ribosome | Linear strand |
| rRNA (Ribosomal RNA) | 🏗️ Forms ribosomes (site of protein synthesis) | Globular |
| tRNA (Transfer RNA) | 🚚 Brings AA → Ribosome, matches codons | Cloverleaf shape |
tRNA Structure
✔ Anticodon → Binds to mRNA codon
✔ 3' End → AA attachment site
✔ Folds into cloverleaf due to internal H-bonding
2.7 CONJUGATED MOLECULES
✔ Complex biomolecules = Protein/Lipid + Other Group
✔ Specialized functions in 🏽 cells
Types of Conjugated Molecules
| Type | Composition | Function | Location |
|---|---|---|---|
| Glycolipids | Lipid + Carbohydrate | 📡 Cell recognition, signaling | 🏗️ Cell membrane, myelin sheath |
| Glycoproteins | Protein + Carbohydrate | 🏥 Hormones, receptors, immunity | 🔬 Cell surface, blood groups |
| Lipoproteins | Lipid + Protein | 🚚 Transport fats/cholesterol | 🩸 Blood plasma, membranes |
| Nucleoproteins | Nucleic acid + Protein | 🧬 Chromosomal structure | 📜 DNA, RNA, Ribosomes |
2.8 APPLICATIONS & CAREERS IN BIOCHEMISTRY
✔ Fields:
- 🏥 Medical Research → Genetic disorders, 🧪 Drug dev.
- 🔬 Forensics → DNA analysis, Toxicology
- 🌾 Food & Agriculture → Nutrition, Crop improvement
- 🌱 Environment → Pollution control, Biofuels
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Exercise | Chapter 2: Biological Molecules | Class 11 Biology
(click any Question to view Answer)
FEQ for Biological Molecules Biology 11th Class
1. Introduction to Biochemistry
- Q2: Definition of biochemistry
- Q3: Bioelements and their significance
- Q4: Chemical composition of protoplasm
2. Water and Its Biological Significance
- Q6: Polarity of covalent bond in water
- Q7: Why water is a universal solvent
- Q8: Importance of hydrogen bonding
- Q9: High heat capacity of water
- Q10: Water’s role in thermal regulation
- Q11: Importance of high heat of vaporization
3. Carbohydrates
- Q12: Classification of carbohydrates
- Q13: Classification of monosaccharides
- Q14: Conversion of ribose from open-chain to ring form
- Q15: Ring forms of α- and β-glucose (diagram)
- Q16: "Left-handed" sugars and their metabolism
- Q17: Formation and hydrolysis of disaccharides (sucrose, maltose, lactose)
4. Proteins and Amino Acids
- Q18: Structural formula of amino acids (diagram)
- Q19: Peptide bond synthesis
- Q20: Four levels of protein structure
- Q21: (a) Globular proteins (b) Fibrous proteins
5. Lipids
- Q22: Classification of lipids
- Q23: Biological role of lipids
- Q24: Phospholipid behavior in aqueous solutions
- Q25: Isoprene unit and its significance
- Q26: Steroid nucleus and its structure
6. Nucleic Acids and Genetics
7. Comparative Biochemistry
- Q29: Differences between:
- (a) Major vs. minor bioelements
- (b) Dimer vs. polymer
- (c) Polar vs. nonpolar covalent bonds
- (d) Polyhydroxy aldehyde vs. polyhydroxy ketone
- (e) α-glucose vs. β-glucose
- (f) D-glucose vs. L-glucose
- (g) Amylase vs. amylopectin
- (h) Amylopectin vs. glycogen
- (i) Primary vs. secondary protein structures
- (j) Tertiary vs. quaternary protein structures
- (k) Purine vs. pyrimidine
- (l) Saturated vs. unsaturated fatty acids
- (m) DNA vs. RNA
#Biomolecules
#Biochemistry
#CellBiology
#Protoplasm
#Macromolecules
#Carbohydrates
#Proteins
#Lipids
#NucleicAcids
#MolecularBiology
