Carbohydrates are made of C, H and O (‘carbo’ – contains carbon ; ‘hydrate’ – contains H and O)

• Carbohydrates are composed of recurring monomers called monosaccharides (‘mono’ – single ; 'saccharide’ – sugar)
  

Monosaccharides typically form ring structures as a result of a chemical reaction between functional groups at opposite ends of the molecule

• A hydroxyl group (-OH) links to a carbonyl group (=O) to form a cyclic structure connected by an oxygen atom
  

Monosaccharide Cyclization

Most monosaccharides have either 5 carbons (pentose sugars) or 6 carbons (hexose sugars)

• The name describes the number of carbons – not the shape (e.g. fructose is a hexose sugar but forms a pentagon)
  

An example of a pentose sugar is ribose – which is a core component of RNA nucleotides and is also found in coenzymes (such as ATP)

• DNA nucleotides have a modified form of this pentose sugar in which an oxygen atom is removed (deoxyribose)
  

An example of a hexose sugar is glucose – which is primarily used as a source of energy (it is digested via cell respiration to produce ATP)

• Glucose can exist as one of two isomers (⍺-D glucose or ß-D glucose) depending on the orientation of the 1’-OH group
  

Pentose vs Hexose Sugars