Biomolecules – Class 11 NCERT PDF
Biomolecules are the organic molecules present in living organisms, essential for various biological functions. These include carbohydrates, proteins, lipids, nucleic acids, vitamins, and enzymes.
1. Carbohydrates
Carbohydrates are organic compounds composed of carbon (C), hydrogen (H), and oxygen (O) in a 1:2:1 ratio. They are the primary source of energy.
Types of Carbohydrates:
1. Monosaccharides (Simple sugars) – Cannot be hydrolyzed further.
• Examples: Glucose, Fructose, Galactose
• Glucose (C₆H₁₂O₆) is the most common energy source in cells.
2. Disaccharides – Formed by the condensation of two monosaccharides.
• Examples: Sucrose (Glucose + Fructose), Lactose (Glucose + Galactose), Maltose (Glucose + Glucose)
3. Polysaccharides – Long chains of monosaccharides.
• Storage Polysaccharides: Starch (Plants), Glycogen (Animals)
• Structural Polysaccharides: Cellulose (Plants), Chitin (Exoskeleton of Arthropods)
2. Proteins
Proteins are polymers of amino acids linked by peptide bonds. They perform structural and functional roles in cells.
Structure of Amino Acids
• Contains amino group (-NH₂), carboxyl group (-COOH), hydrogen (-H), and an R group (variable side chain).
• 20 types of amino acids exist in nature.
Levels of Protein Structure:
1. Primary Structure – Linear sequence of amino acids.
2. Secondary Structure – Alpha-helix or beta-pleated sheet due to hydrogen bonding.
3. Tertiary Structure – 3D folding of the polypeptide chain.
4. Quaternary Structure – Multiple polypeptide chains interact.
Examples: Hemoglobin, Enzymes, Collagen, Insulin.
3. Lipids
Lipids are hydrophobic organic molecules that serve as energy reserves, membrane components, and signaling molecules.
Types of Lipids:
1. Simple Lipids (Fats and Oils) – Composed of glycerol and fatty acids.
• Saturated Fats: No double bonds (e.g., Butter).
• Unsaturated Fats: One or more double bonds (e.g., Olive oil).
2. Complex Lipids – Include phospholipids, glycolipids.
• Phospholipids: Form cell membranes (e.g., Lecithin).
3. Derived Lipids – Steroids, cholesterol, vitamins (A, D, E, K).
4. Nucleic Acids
Nucleic acids are polymers of nucleotides responsible for genetic information storage and transmission.
Types of Nucleic Acids:
1. DNA (Deoxyribonucleic Acid) – Genetic material in most organisms.
• Double-stranded helix, composed of Adenine (A), Thymine (T), Guanine (G), Cytosine (C).
• A pairs with T, G pairs with C (Complementary base pairing).
2. RNA (Ribonucleic Acid) – Single-stranded, involved in protein synthesis.
• Contains Uracil (U) instead of Thymine (T).
• Types: mRNA (Messenger RNA), tRNA (Transfer RNA), rRNA (Ribosomal RNA).
5. Enzymes
Enzymes are biocatalysts that speed up biochemical reactions without being consumed.
Characteristics of Enzymes:
• Highly specific in action.
• Work by lowering activation energy.
• Affected by temperature, pH, and substrate concentration.
Enzyme Action Mechanism:
1. Lock and Key Model – Substrate fits perfectly into the active site.
2. Induced Fit Model – Active site changes shape to accommodate the substrate.
Examples: Amylase, Lipase, Pepsin, Trypsin.
6. Vitamins
Vitamins are organic compounds required in small amounts for various metabolic processes.
Types of Vitamins:
1. Water-Soluble Vitamins – Vitamin B-complex and Vitamin C.
2. Fat-Soluble Vitamins – Vitamins A, D, E, K.
Vitamin Deficiency Disease
Vitamin A Night Blindness
Vitamin B1 (Thiamine) Beriberi
Vitamin C Scurvy
Vitamin D Rickets
Vitamin K Blood Clotting Issues
7. Metabolism – Anabolism and Catabolism
• Anabolism: Synthesis of complex molecules (e.g., Protein synthesis, Photosynthesis).
• Catabolism: Breakdown of molecules (e.g., Glycolysis, Respiration).
ATP (Adenosine Triphosphate)
ATP is the energy currency of the cell, used in metabolic reactions.
Conclusion
Biomolecules are essential for life, performing structural, functional, and regulatory roles. Understanding them helps in learning how life functions at the molecular level.
These NCERT Class 11 notes provide a summary of biomolecules, important for NEET, CBSE exams, and competitive exams.
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