Carbohydrate Classification and Monosaccharides

Carbohydrate Classification

• Carbohydrates are classified based on the presence of aldehyde or ketone groups, number of carbons, and number of sugar units.
• Aldoses contain an aldehyde group, while ketoses contain a ketone group.
• Aldoses and ketoses can be further classified based on the number of carbons present in the molecule.

Monosaccharides

• Monosaccharides are the simplest form of sugar.
• They are classified based on the number of carbons they contain.
• Triose monosaccharides contain 3 carbons, tetrose monosaccharides contain 4 carbons, pentose monosaccharides contain 5 carbons, and hexose monosaccharides contain 6 carbons.

Examples of Monosaccharides

• Glyceraldehyde: Aldotriose - Dihydroxyacetone: Ketotriose
• Erythrose: Aldotetrose - Erythrulose: Ketotetrose
• Ribose & Xylose: Aldopentose - Ribulose & Xylulose: Ketopentose
• Glucose, Galactose, Mannose: Aldohexose - Fructose: Ketohexose

Isomerism

• Isomers are compounds with the same molecular formula but different structural formulas.
• Enantiomers are mirror images of each other. For example, D-glucose and L-glucose are enantiomers.
• Epimers differ in their configuration around only one carbon. For example, D-glucose and D-mannose are epimers at C2, and D-glucose and D-galactose are epimers at C4.
• Aldose-ketose isomers differ in their functional groups. For example, glucose and fructose are aldose-ketose isomers.

Monosaccharide Derivatives

• Monosaccharides can undergo various modifications to form derivatives with different functions:
  • Sugar Acids: Oxidation of aldehyde group forms aldonic acids (e.g., Gluconic acid), oxidation of primary alcohol group forms uronic acids (e.g., Glucuronic acid) and oxidation of both forms aldaric acids (e.g., Glucaric acid).
  • Sugar Alcohols: Reduction of carbonyl group to alcohol group. For example, Glucose is reduced to Sorbitol.
  • Deoxy Sugars: Replacement of hydroxyl group with a hydrogen atom. For example, Deoxyribose is found in DNA.
  • Amino Sugars: Replacement of hydroxyl group with an amino group. For example, Glucosamine is a component of glycosaminoglycans.
  • Ester Formation: Addition of phosphate groups. For example, Glucose 6-Phosphate.
  • Glycosides: Condensation of sugars with other molecules. For example, disaccharides and polysaccharides.

Biomedical Importance of Carbohydrates

• Carbohydrates serve as the primary energy source for plants and animals.
• Glucose is the most crucial carbohydrate, as most dietary carbohydrates are absorbed as glucose.
• Other key functions include:
  • Cell membrane components
  • Structural tissues in plants and microorganisms
  • Precursors for the synthesis of other carbohydrates

Types of Chemical Bonds

• Covalent bonds: Involve sharing of electron pairs. Strong bonds requiring high energy to break.
• Non-covalent bonds: Do not involve electron sharing. Examples include:
  • Ionic Interactions
  • Hydrophobic Interactions
  • Hydrogen Bonds
  • Van der Waals forces