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Chem-153L-Organic-Biochem-Midterm-Discussion-1st-Semester-SY2024-2025

Carbohydrates

Definition

  • Carbohydrates: Polyhydroxy aldehydes or ketones that serve as a major source of energy in our diet.

    • Yield simple sugars upon hydrolysis.

Types of Carbohydrates

Monosaccharides

  • Simple sugars that cannot be hydrolyzed into smaller sugars.

  • All free monosaccharides are reducing sugars.

  • Key monosaccharides used in experiments:

    • Arabinose (aldopentose)

    • Glucose (aldohexose)

    • Fructose (ketohexose)

    • Galactose (aldohexose)

Characteristics of Monosaccharides

  • Arabinose: Component of plant polysaccharides (gums), found in coniferous trees.

  • Glucose: Also known as grape sugar (found in grapes) and blood sugar.

  • Fructose: Fruit sugar, the sweetest of all sugars.

  • Galactose: Also known as cerebrose, present in cerebrosides (glycolipids in nerve cells).

Oligosaccharides

  • Composed of 2 to 10 simple sugars linked by glycosidic bonds.

  • Common examples:

    • Maltose: Glucose + Glucose (malt sugar)

    • Lactose: Glucose + Galactose (milk sugar)

    • Sucrose: Glucose + Fructose (table sugar)

Polysaccharides

  • Composed of nine or more monosaccharides linked by glycosidic bonds.

  • Functions: Structural or nutrient.

  • Common polysaccharides:

    • Starch: Found in seeds, tubers, and roots.

      • Components: Amylose (unbranched, helical) and Amylopectin (highly branched).

    • Glycogen: Animal storage form of glucose.

    • Cellulose: Most abundant organic compound, found in plant cell walls.

    • Agar-agar: Used in microbiology and food industry.

    • Gum-arabic: Used as adhesive and thickening agent.

General Tests for Carbohydrates

Molisch Test

  • Color test for sugars, producing a purple color at the interface with sulfuric acid.

Iodine Test

  • Distinguishes helical from non-helical polysaccharides.

  • Positive result: Blue-black color with starch, brown-blue with glycogen.

Benedict’s Test

  • General test for reducing sugars.

  • Formation of deep-red Cu2O precipitate indicates a positive result (except for sucrose).

Barfoed’s Test

  • Uses Cu2+ in slightly acidic medium. Reducing monosaccharides yield a positive result:

    • Green, red, or yellow precipitate indicates reducing sugars (monosaccharides).

Seliwanoff’s Test

  • Distinguishes aldoses from ketoses. Ketoses form a cherry-red product with resorcinol in acidic conditions.

Orcinol Test

  • Distinguishes pentoses from hexoses; a blue-green color indicates a positive result.

Summary of Tests

  • Osazone Test: Distinguishes sugars based on crystalline forms produced with phenylhydrazine.

  • Mucic Acid Test: Converts aldohexoses like galactose to dicarboxylic acids (mucic acid) in presence of oxidizing agents.

Lipids

Definition and Functions

  • Lipids: Biomolecules that include fats, oils, sterols, and vitamins, performing functions like energy storage, heat insulation, and membrane formation.

Types of Lipids

  • Fatty Acids: Long-chain carboxylic acids, can be saturated or unsaturated.

  • Triglycerides: Composed of three fatty acids and glycerol; fats (solid) and oils (liquid).

  • Phospholipids: Major plasma membrane components with hydrophobic tails and hydrophilic heads.

  • Steroids: Characterized by four fused rings, including hormones and cholesterol.

Lipid-Soluble Vitamins

  • A (retinol), E (tocopherol), D (calciferol), K (phylloquinone).

  • Accumulate in body, may reach toxic levels.

Tests for Lipids

Acrolein Test

  • Tests for presence of glycerin or fats, releasing acrolein (irritating smell) upon heating.

Unsaturation Test

  • Addition of Hubl’s solution to detect unsaturated fatty acids; changes color upon saturation.

Phosphate Test

  • Detects phospholipids with ammonium molybdate yielding a yellow precipitate.

Emulsification

  • Formation of emulsions (liquid suspensions). Emulsifiers like bile salts aid in creating stable mixtures.

Lieberman-Burchard Test

  • Cholesterol reacts with acetic anhydride in acidic conditions, producing a blue-green solution.

Isolation and Purification of Proteins

Composition of Milk

  • Contains proteins (caseins, lactalbumins), vitamins, minerals, carbohydrates, and lipids.

Casein Protein

  • Makes up about 80% of milk proteins. Stabilized against heat denaturation due to lack of tertiary structure.

Uses of Casein

  • Source of protein, aids in emulsification, used in wine-making for clarification, and can be formed into plastics.

Isolation Process

  • Heating milk, adding acid to reach casein's isoelectric point for coagulation, yielding curds and whey, straining, and drying processes.