Carbohydrates in Biochemistry

Carbohydrates

• Organic molecules containing carbon, hydrogen, and oxygen
• Formed by green plants during photosynthesis from CO2 and water
• General formula: C(H2O)n, meaning "watered carbon"
• Also known as "saccharide" or sugars
• Major source of energy from diet

Importance of Carbohydrates

• Widely distributed in nature
• Key intermediates of metabolism (sugars)
• Structural components of plants (cellulose)
• Central to industrial products (paper, fibers)
• Key component of food sources (sugars, flour, vegetable fiber)

Classification of Carbohydrates

• Simple sugars (monosaccharides): contain one unit (e.g., glucose, fructose)
• Complex sugars:
  • Disaccharides: contain two units (e.g., sucrose, lactose, maltose)
  • Oligosaccharides: contain 3-9 units (e.g., raffinose)
  • Polysaccharides: contain more than 9 units (e.g., starch)

Reducing and Non-Reducing Sugars

• Reducing sugars: have free aldehyde or ketose group (e.g., glucose, galactose, fructose, lactose, maltose)
• Non-reducing sugars: lack free aldehyde or ketose group (e.g., sucrose, oligosaccharides, polysaccharides)

Tests for Carbohydrates

Molisch's Test

• General test for all carbohydrates
• Principle: dehydration of carbohydrates into furfural compounds in strong acid, reacting with α-naphthol to form a violet-colored ring
• Procedure: 1 ml sugar, 5 drops α-naphthol, 10 drops H2SO4 slowly

Benedict's Test

• Test for reducing sugars
• Principle: reduction of cupric ion into cuprous oxide in hot alkaline medium, causing color change and red precipitate formation
• Procedure: 0.5 ml sugar solution, 1 ml Benedict's reagent, boiling water bath for 3 minutes

Barfoed's Test

• Distinguishes mono from disaccharides
• Principle: reduction of cupric ion in Barfoed's reagent faster by monosaccharides than disaccharides in hot acidic medium
• Procedure: 1 ml sugar solution, 1 ml Barfoed's reagent, boiling water bath for 2-3 minutes

Seliwanoff's Test

• Distinguishes between ketoses and aldoses
• Principle: ketoses are more rapidly dehydrated than aldoses when heated
• Used to identify ketoses and aldoses

Learn about carbohydrates, their definition, formation, and importance. Explore their structure, function, and role as a major source of energy.