Glucose and Disaccharides – Biological Molecules Ep 7

Glucose is a really important carbohydrate for living organisms because it is a reactant in respiration. It is a monosaccharide – a single sugar monomer that can be used to build other types of carbohydrates called polysaccharides. We will cover polymers of glucose in a separate article – today we will look at the structure of glucose and how it can form disaccharides.

Glucose

Glucose is a hexose sugar, meaning it contains six carbon atoms (remember nucleotides contain pentose sugars which have five carbon atoms). You might remember from the respiration equation that glucose has the formula C6H1206. The diagram shows it’s structure.

The structure of α-glucose

However, glucose has two isomers called α-glucose and β-glucose. In β-glucose, the H and OH groups on the far right carbon are reversed.

Disaccharides

Disaccharides are sugars made from two monosaccharides. Joining two molecules of glucose together produces a disaccharide called maltose. Similar to joining amino acids together, the glucose molecules join to each other in a condensation reaction (so water is a product), but form a glycosidic bond. Important disaccharides to remember are:

  • Maltose = glucose + glucose
  • Sucrose = glucose + fructose
  • Lactose = glucose + galactose

As with other condensation reactions we’ve learnt about, the reverse is a hydrolysis reaction which adds a molecule of water to break the bond between the monomers.

Joining two glucose molecules with a condensation reaction to produce maltose and water

Glucose is easily transported around the body because it is soluble in water. It also contains lots of energy stored in its chemical bonds which makes it a great energy source. Sometimes this energy needs to be stored in insoluble carbohydrates, which is when glucose polymers are formed.

Summary

  • Glucose is a hexose sugar which has two isomers – α-glucose and β-glucose.
  • A glycosidic bond forms between two glucose molecules when they are joined with a condensation reaction to form a disaccharide (maltose) and water.
  • Glucose is soluble and stores a lot of energy in its chemical bonds, making it a good energy source.

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