Higher sugars and polymers

With few exceptions, sugars react with other sugars by using the alpha or beta OH on the ring. Some important disaccharides are :

LACTOSE (milk sugar)
The left ring is a locked hemiacetal, but the other ring can open. This is a reducing sugar. Explanation of reducing sugars. Galactose is part of nerve and brain biochemicals, so milk is essential to infants.

Here is cane sugar, the disaccharide SUCROSE. Both rings are locked. This is a non-reducing sugar. Sucrose is sweet, but fructose is the sweetest natural sugar. Note the 5-member ring.


When a glucose reacts with another glucose using the alpha OH on one to combine with the #4 OH on the other, the product is D-MALTOSE. One of its OH groups from the formation of a hemiacetal is still intact, so it can exist with that sugar in an open chain or as a ring. The former glucose on the left, however, is locked so that it cannot open. It is always a ring.THE LINK IS ALPHA 1-4. The ring on the right can open, so this is a reducing sugar. Note that maltose is the repeating unit in starch.

  • Move on to starch and cellulose.
  • Back to review ring structures.