Biological Compounds and Biomolecules

Chemical Elements and Biological Compounds

• Chemical elements combine to create biological compounds essential for life.

Water Properties

• Water (H₂O) as a polar molecule

  • Allows hydrogen bonds, providing significant properties.

  • Solvent: Polar molecules dissolve in water, facilitating transport.

  • Metabolite: Acts as a reactant in photosynthesis, hydrolysis, and is produced in respiration and condensation reactions.

  • High Specific Heat Capacity: Requires considerable energy to change temperature, stabilizing aquatic and cellular environments.

  • High Latent Heat of Vaporisation: Provides evaporative cooling, aiding temperature regulation.

  • Surface Tension: Important for support and buoyancy in various organisms.

Carbohydrates

• Monosaccharides: Simple sugars, building blocks of carbohydrates.

  • Types:

  • Triose (3C): Important in respiration and photosynthesis.

  • Pentose (5C): Key in nucleotides (like ribose).

  • Hexose (6C): Includes glucose, essential in respiration.

• Disaccharides: Formed by linking monosaccharides via condensation reactions, resulting in glycosidic bonds.

  • Examples:

  • Sucrose: Glucose + Fructose; transport sugar in plants.

  • Maltose: Glucose + Glucose.

  • Lactose: Glucose + Galactose; found in milk.

• Polysaccharides: Long chains of monosaccharides, serving as energy storage or structural components.

  • Starch: Polymer of α-glucose; energy storage in plants, low osmotic effect.

  • Glycogen: Polymer of α-glucose; energy storage in animals.

  • Cellulose: Polymer of β-glucose; forms strong plant cell walls via hydrogen bonding.

  • Chitin: Similar to cellulose but with nitrogen, forming exoskeletons; strong yet lightweight.

Testing for Carbohydrates

• Starch: Iodine solution turns blue/black if positive.

• Reducing sugars: Benedict's reagent turns colors based on sugar presence (blue to red); non-reducing sugars require hydrolysis in acid.

Proteins

• Composed of 20 different amino acids.

  • Amino Acid Structure: Contains an amino group, carboxyl group, and variable R group.

  • Dipeptide: Formed when two amino acids are linked.

  • Polypeptide: A chain of amino acids, folded into specific shapes.

  • Primary Structure: Sequence of amino acids as per DNA coding.

  • Secondary Structure: Folding into alpha-helices or beta-pleated sheets due to hydrogen bonds.

  • Tertiary Structure: 3D structure formed through interactions (hydrophobic, ionic, disulfide bonds).

  • Quaternary Structure: Assembly of multiple polypeptide chains.

  • Types of Proteins:

    • Fibrous proteins: Structural (e.g., keratin).

    • Globular proteins: Functional (e.g., enzymes).

• Test for Proteins: Biuret test - blue solution turns purple with proteins.

Lipids

• Triglycerides: Composed of glycerol and 3 fatty acid chains linked by ester bonds.

  • Functions: Energy storage, insulation, protection.

• Phospholipids: Composed of glycerol, 2 fatty acids, and a phosphate group.

  • Properties: Hydrophilic head, hydrophobic tail; forms lipid bilayer in membranes.

• Fatty Acids:

  • Saturated: Single carbon-to-carbon bonds.

  • Unsaturated: Contains one (mono-) or more (poly-) double bonds.

  • Health Implications: High saturated fat intake can raise LDL cholesterol, increasing heart disease risk.

• Testing for Lipids: Mix with ethanol and water; a cloudy emulsion indicates lipids present.

Inorganic Ions

• Vital for various biological functions. Examples include:

  • Magnesium (Mg²⁺): In chlorophyll.

  • Iron (Fe²⁺): In hemoglobin.

  • Calcium (Ca²⁺): Strengthens bones and teeth; supports plant cell walls.