SPM Biology 4 Chemical Composition of the Cell Part 2 Organic Compounds in the Cell - Carbohydrates

Organic compounds - chemical compounds that contain carbon (C) elements.

Monomers - building blocks for polymers

Polymers - materials made of long, repeating chains of molecules.

Organic Compounds in the Cell - Carbohydrates

Foods that contain carbohydrates

• Made up of carbon, hydrogen & oxygen
• Ratio of hydrogen atoms to oxygen atoms in one molecule of carbohydrate is 2:1
• Importance: as storage and supply of energy
• 3 main types of carbohydrates: monosaccharides, disaccharides, polysaccharides

3 main types of carbohydrates

Monosaccharides (Simple Sugar)

• General formula: (CH₂O)_n , where n = 3 , 5 / 6 carbon atoms in the molecule
• Most common = 6-carbon sugar / hexoses (C₆H₁₂O₆)
• Soluble in water, sweet, and form crystals
• Can combine with protein & lipids to form glycoproteins & glycolipids (part of plasma membrane)
• All monosaccharides are reducing sugar!!
• Examples:

Monosaccharides

Disaccharides

• 2 monosaccharides form disaccharides, by removing a molecule of water (condensation)
• Formula: C₁₂H₂₂O₁₁
• It can be broken down to monosaccharides by adding water (hydrolysis)
• Water soluble, sweet, form crystals
• Maltose and lactose are reducing sugar, sucrose is not !!
• Examples:

Disaccharides

Polysaccharides

• Polymers that consisting of chains of monosaccharides
• General formula: (C₆H₁₀O₅)_n , where n varies from 40 to several thousands
• Can be hydrolyzed to monosaccharides by heating with acid / enzymatic reactions
• Insoluble in water, ✗ sweet, cannot be crystallized
• Iodine solution is used to test for the presence of starch
• Examples:

Polysaccharides

Condensation and hydrolysis 

★ Reducing Sugar ★ [Any carbohydrate whose structure contains an aldehyde, or a hemiacetal in equilibrium with an aldehyde]

Define: sugars that can act as reducing agents.

Examples of reducing sugar's structure

Test for a reducing sugar: Benedict’s solution

• When sugar solution is heated with Benedict’s solution, formation of a brick-red precipitate indicates a reducing sugar is present.

Benedict`s test