Carbohydrates and Their Types

Carbohydrates

• Polyhydroxy aldehyde or ketone or a compound that yields polyhydroxy aldehydes and polyhydroxy ketones on hydrolysis.
• Commonly known as sugars because most of them have a sweet taste.
• Serves as a major source of energy.
• Furnishes the carbon chains of compound synthesis.
• Found in nature and function either as:
  • Bioorganic compounds
    • Proteins
    • Lipids
    • Nucleic Acids
  • Categorized as
    • Monosaccharides
    • Disaccharides
    • Polysaccharides

Monosaccharides

• Highly soluble in water.
• Less soluble in ethanol.
• Insoluble in ether.
• Aldoses or ketoses.
• Free monosaccharides are all reducing sugars.

Disaccharides

• Formed by two molecules of monosaccharides.
• Examples include:
  • Maltose (Glucose + Glucose) – abundant in germinating barley.
  • Sucrose (Fructose + Glucose) – also known as table sugar / cane sugar / beet sugar.
  • Lactose or Milk Sugar (Galactose + Glucose) – does not taste very sweet and is not fermented by yeast.

Polysaccharides

• Structural polysaccharide:
  • Cellulose
• Storage polysaccharide:
  • Starch
  • Dextrin
  • Glycogen
  • Insulin

Midterm Lab: Carbo Part 1 - Tests Based on Furfural & Its Derivatives

• Tests are based on furfural and its derivatives.
• Principle: Hot H2SO4 will dehydrate sugars into furfural and its derivatives.

Molisch Test

• General test for carbohydrates.
• Molisch reagent contains 𝛂-naphthol.
• Positive result: formation of purple ring.
• Concentrated H2SO4 will dehydrate the sugar, allowing it to react with the alcohol forming furfural or hydroxymethyl-furfural.

Bial’s Orcinol Test

• Determines the presence of pentoses, but not specific.
• Distinguishes pentose monosaccharide and hexose monosaccharide.
• The reaction is not specific for pentoses because other compounds like trioses, uronic acids, and certain heptoses will also give blue or green products.
• Positive result:
  • Pentoses + Orcinol → Blue Green Compound (HCl & Resorcinol)
  • Ketohexoses + Condensation Product → Cherry Red
  • Hexoses + Orcinol → Yellow Brown Pigment (HCl & Resorcinol)
  • Aldohexoses + Condensation Product → Pale Pink

Seliwanoff’s Test

• Used to differentiate ketohexoses from aldohexoses.
• Ketohexoses react faster with the solution of hydrochloric acid and resorcinol than aldohexoses.
• Positive result:
  • Ketohexoses reaction: Cherry Red
  • Aldohexoses reaction: Pale Pink

Midterm Lab: Carbo Part 2 — Tests Based on the Reducing Properties of Sugars

• Used for sugars with aldehydes.
• Benedict's reagent:
  • CuSO4 (copper sulfate)
  • Na2CO3 (sodium carbonate)
  • Na3C6H5O7 sodium citrate
• Positive compounds:
  • Brick Red Precipitate Cu2O (copper)

Isolation of RNA from Yeast

• To isolate RNA from yeast.
• To test properties of the isolated RNA.
• Procedure:
  1. Add 10 g of baker’s yeast in a mortar.
  2. Grind the yeast with 5 ml of 0.2% NaOH using a pestle.
  3. Pour the mixture in a beaker and dilute with 0.2% NaOH solution to make 50 mL.
  4. Cover the beaker with a watch glass to avoid evaporation.
  5. Heat the beaker in a water bath with a constant temperature of 90°C for 30 minutes.
  6. Filter the solution thrice using cheesecloth and once through a filter paper.
  7. Allow the filtrate to cool → RNA EXTRACT (RE).
  8. Perform the following tests on the filtrate (RE).

Qualitative Tests: Test for Nucleoproteins (Biuret’s Test)

• Nucleoproteins are any proteins that are structurally associated with nucleic acids either DNA or RNA.
• Procedure:
  1. Add 1 mL of the filtrate (RE) in a test tube.
  2. Add 2 drops of 10% NaOH.
  3. Add 2 drops of 1% CuSO4 (copper sulfate solution).