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Short Notes: Biomolecules
1.1 Carbohydrates
| Type | Definition | Examples |
|---|---|---|
| Monosaccharides | Simplest carbohydrates; cannot be hydrolyzed further | Glucose, Fructose, Ribose, Galactose |
| Disaccharides | Formed by 2 monosaccharides; yield 2 molecules on hydrolysis | Sucrose, Maltose, Lactose |
| Polysaccharides | Formed by many monosaccharides; yield many molecules on hydrolysis | Starch, Cellulose, Glycogen |
1.2 Important Reactions of Glucose
- Acetylation: Glucose + 5(CH3CO)2O → Glucose pentaacetate
- Oxidation:
- With Br2 water → Gluconic acid (aldehyde to acid)
- With HNO3 → Saccharic acid (both ends oxidized)
- Reduction: Glucose + H2/Ni → Sorbitol (hexahydric alcohol)
- Glycoside Formation: Glucose + CH3OH/HCl → Methyl glucoside
- Cyanohydrin Formation: Proves presence of carbonyl group
1.3 Disaccharides
| Disaccharide | Composition | Linkage | Reducing/Non-reducing |
|---|---|---|---|
| Sucrose | α-Glucose + β-Fructose | α(1→2) glycosidic | Non-reducing (no free CHO/CO) |
| Maltose | α-Glucose + α-Glucose | α(1→4) glycosidic | Reducing (free CHO present) |
| Lactose | β-Galactose + β-Glucose | β(1→4) glycosidic | Reducing (free CHO present) |
1.4 Polysaccharides
- Starch:
- Amylose: 15-20%, unbranched, α(1→4) linkage, helical structure
- Amylopectin: 80-85%, branched, α(1→4) and α(1→6) linkage
- Gives blue color with iodine
- Cellulose:
- β(1→4) glycosidic linkage between β-D-glucose units
- Unbranched, linear polymer
- Does not give color with iodine
- Hydrolysis gives cellubiose then glucose
- Glycogen:
- Animal starch, stored in liver and muscles
- Highly branched structure
1.5 Amino Acids
| Property | Details |
|---|---|
| General Structure | R-CH(NH2)-COOH |
| Classification (R group) | Acidic (Glu, Asp), Basic (Lys, Arg), Neutral (Gly, Ala) |
| Essential Amino Acids | 10 amino acids that cannot be synthesized by body (e.g., Valine, Leucine, Phenylalanine) |
| Zwitterion | Dipolar ion with +NH3 and COO- groups |
| Isoelectric Point | pH at which amino acid exists as zwitterion (no migration in electric field) |
1.6 Proteins
Protein Structure Hierarchy:
- Primary (1°): Linear sequence of amino acids joined by peptide bonds
- Secondary (2°): α-helix or β-pleated sheet (H-bonding between peptide groups)
- Tertiary (3°): 3D folding of protein chain (H-bonds, disulfide bridges, ionic bonds)
- Quaternary (4°): Assembly of multiple polypeptide chains (e.g., Hemoglobin)
1.7 Protein Classification
| Type | Solubility | Examples |
|---|---|---|
| Fibrous Proteins | Insoluble in water | Keratin, Myosin, Collagen |
| Globular Proteins | Soluble in water | Insulin, Albumin, Globulin |
1.8 Denaturation of Proteins
- Definition: Loss of biological activity due to disruption of secondary and tertiary structure
- Causes: Heat, pH change, chemicals, UV radiation
- Effect: Unfolding of protein chain; primary structure remains intact
1.9 Enzymes
- Biocatalysts: Protein molecules that catalyze biochemical reactions
- Characteristics:
- Highly specific in action
- Most effective at optimum temperature (37°C) and pH (7-8)
- Denatured by high temperature
- Examples: Invertase, Maltase, Lactase, Urease, Pepsin, Trypsin
1.10 Nucleic Acids
| Component | DNA | RNA |
|---|---|---|
| Sugar | β-D-2-deoxyribose | β-D-ribose |
| Bases | Adenine, Guanine, Cytosine, Thymine | Adenine, Guanine, Cytosine, Uracil |
| Structure | Double helix (Watson-Crick model) | Single stranded |
| Location | Nucleus | Nucleus and cytoplasm |
| Function | Genetic information storage | Protein synthesis |
1.11 DNA Base Pairing (Chargaff's Rule)
- Adenine (A) pairs with Thymine (T) - 2 hydrogen bonds
- Guanine (G) pairs with Cytosine (C) - 3 hydrogen bonds
- Amount of A = T and G = C
- Amount of purines = pyrimidines
1.12 Vitamins
| Vitamin | Type | Deficiency Disease | Source |
|---|---|---|---|
| A (Retinol) | Fat-soluble | Night blindness, Xerophthalmia | Fish liver oil, carrots, milk |
| B1 (Thiamine) | Water-soluble | Beriberi | Yeast, cereals, pulses |
| B2 (Riboflavin) | Water-soluble | Cheilosis, glossitis | Milk, eggs, green vegetables |
| B6 (Pyridoxine) | Water-soluble | Convulsions, skin disorders | Yeast, milk, cereals |
| B12 (Cyanocobalamin) | Water-soluble | Pernicious anemia | Meat, fish, eggs |
| C (Ascorbic acid) | Water-soluble | Scurvy | Citrus fruits, amla |
| D (Calciferol) | Fat-soluble | Rickets, osteomalacia | Fish liver oil, sunlight |
| E (Tocopherol) | Fat-soluble | Sterility | Vegetable oils, nuts |
| K (Phylloquinone) | Fat-soluble | Increased blood clotting time | Green leafy vegetables |
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FAQs on Short Notes: Biomolecules
| 1. What are the four main types of biomolecules? |  |
Ans. The four main types of biomolecules are carbohydrates, lipids, proteins, and nucleic acids. Each type plays a crucial role in biological processes; carbohydrates provide energy, lipids store energy and form cell membranes, proteins perform a variety of functions including catalysis and structure, and nucleic acids like DNA and RNA store and transmit genetic information.
| 2. How do enzymes function as biological catalysts? | |
Ans. Enzymes function as biological catalysts by lowering the activation energy required for biochemical reactions to occur. They bind to substrates at their active sites, facilitating the transformation of substrates into products while remaining unchanged themselves. This increases the reaction rate without altering the equilibrium of the reaction.
| 3. What is the significance of amino acids in proteins? | |
Ans. Amino acids are the building blocks of proteins. Each protein is composed of a specific sequence of amino acids, which determines its structure and function. There are 20 different amino acids, and their arrangement leads to the formation of various proteins, which are essential for processes such as enzymatic reactions, immune responses, and cellular structure.
| 4. What are the roles of carbohydrates in living organisms? | |
Ans. Carbohydrates serve several important roles in living organisms. They are primarily a source of energy; monosaccharides like glucose are used in cellular respiration to produce ATP. Additionally, carbohydrates serve structural roles in plants (as cellulose) and fungi (as chitin), and they also play a key role in cell recognition and signalling through glycoproteins and glycolipids.
| 5. How do lipids differ from carbohydrates in terms of structure and function? | |
Ans. Lipids differ from carbohydrates in their structure and function. Lipids are hydrophobic molecules primarily composed of long hydrocarbon chains or rings, whereas carbohydrates are typically polar and consist of carbon, hydrogen, and oxygen in a 1:2:1 ratio. Functionally, lipids are involved in long-term energy storage, forming cell membranes, and acting as signalling molecules, whereas carbohydrates mainly provide quick energy and serve as structural components.
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