Modifications of Sugar Molecules

Importance of Sugar Modification

• Modifying sugar molecules alters properties and functionalities.
• Crucial in various bodily processes, such as glucose metabolism.

Key Sugar Modifications

1. Phosphorylation of Sugars
2. Glycosylation of Sugars

Phosphorylation of Sugars

• Glucose Metabolism Step 1: Convert glucose to glucose 6-phosphate.
  • Involves phosphorylating glucose (adding phosphate to carbon 6).
• Differences between Glucose and Glucose 6-Phosphate:
  • Glucose 6-phosphate has a net negative charge (-2).
  • More reactive, higher energy, less stable.
  • Prevents glucose from spontaneously exiting the cell due to increased polarity.
  • Polarity prevents glucose 6-phosphate from crossing the cell membrane (non-polar lipids).

Glycosylation of Sugars

• Beta Anomer of Glucose
  • Exists in stable cyclic form.
  • Less than 1% in open chain form containing aldehyde group.
• Role of Aldehyde Group:
  • Reactive in presence of oxidizing agents (e.g., copper ion).
  • Converts to carboxylic acid, making it a reducing sugar.
• Glycosylation Process:
  • Removes aldehyde group, preventing unwanted reactions.
  • Forms glycosides in presence of alcohol and acid.
  • Glycosides: Methyl β-D-glucopyranoside and Methyl α-D-glucopyranoside (anomers).
  • Bond between carbon 1 and oxygen is an O-glycosidic bond.

Non-Reducing Sugars

• Purpose: Prevents glucose from reacting with oxidizing agents.
• Result: Non-reducing sugars lack aldehyde group in open chain form.
• O-glycosidic Bonds:
  • Formed with alcohols.
  • Prevent reducing property by removing aldehyde.

N-glycosidic Bonds

• Formed with Amines:
  • Reaction of anomeric carbon with amines forms N-glycosidic bond.
  • No aldehyde group, preventing reducing sugar behavior.

Conclusion

• Sugar modifications (phosphorylation, glycosylation) control properties/reactivity.
• Important for regulating cellular processes and stability.