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.