Biological Molecules | Best 11th Class Biology Notes | Federal Board
Chapter 2 :
BIOLOGICAL MOLECULES
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
Bioelement 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
- 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
