Carbohydrates - monosaccharides

Carbohydrates

• Carbon, Hydrogen and Oxygen (Carbon bonded to water)

• Put into groups depending on their size

• Used as energy sources, stores, and structural materials

Monosaccharides

• Simple carbohydrates

• White crystals

• Sweet tasting

• Soluble

Glucose

• Very soluble

• Easily transported

• Major energy source

• Broken down in respiration

Galactose

• Less soluble

• Used in production of glycolipids and glycoproteins

Fructose

• Very soluble

• Sweeter than glucose

• Main sugar in fruits and nectar

Monosaccharide chemical formula

(CH2O)n - where n = number of carbons between 1-7

Isomer

The same chemical formula but a different structure (i.e for glucose alpha and beta)

Test for monosaccharides

• They are all reducing sugars

• Heated with benedict’s solution (Copper II sulphate) to form an insoluble red precipitate of copper (I) oxide.

Disaccharides

alpha-glucose + alpha-glucose →

glucose + galactose →

glucose + fructose →

maltose

lactose

sucrose

Carbohydrate polymerisation

Type of reaction:

Covalent bond formed:

Role of water:

Condensation

Glycosidic

Removed

Carbohydrate Digestion

Type of reaction:

Covalent bond broken:

Role of water:

Hydrolysis

Glycosidic

Used/added

Testing for disaccharides

They are NOT reducing sugars so must be hydrolysed into monosaccharides to generate a positive benedict’s solution reaction:

• Add HCL

• Heat for 5’

• Neutralise with sodium hydrogen carbonate - drop by drop until fizzing stops

• Add benedict’s solution

• Heat for 5’

• Negative control is water

• Brick red - positive