Edexcel A (SNAB) A Level Biology:复习笔记1.2.7 Disaccharides

Disaccharides: Structure

  • Two monosaccharides can join together via condensation reactions to form disaccharides
    • A condensation reaction is one in which two molecules join together via the formation of a new chemical bond, with a molecule of water being released in the process
    • The new chemical bond that forms between two monosaccharides is known as a glycosidic bond
  • Common examples of disaccharides include
    • Maltose
      • Contains two molecules of glucose linked by a 1,4 glycosidic bond
        • This means that the glycosidic bond is located between carbon 1 of one monosaccharide and carbon 4 of the other
    • Sucrose
      • Contains a molecule of glucose and a molecule of fructose linked by a 1,2 glycosidic bond
        • This means that the glycosidic bond is located between carbon 1 of one monosaccharide and carbon 2 of the other
    • Lactose
      • Contains a molecule of glucose and a molecule of galactose linked by a 1,4 glycosidic bond

 

Sucrose is a disaccharide formed from a molecule of glucose (left) and a molecule of fructose (right) joined together by a 1,2 glycosidic bond

 

Disaccharides: Function

  • The function of disaccharides is to provide the body with a quick-release source of energy
    • Disaccharides are made up of two sugar molecules so they're easily broken down by enzymes in the digestive system into their respective monosaccharides and then absorbed into the bloodstream
  • Due to the presence of a large number of hydroxyl groups, disaccharides are easily soluble in water
    • These hydroxyl groups form hydrogen bonds with the water molecules when dissolved in aqueous solutions
  • Just like monosaccharides they are sweet in taste
    • Sucrose, also known as table sugar, is an example

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