Lecture on Carbohydrates

Definition and Composition

• Carbohydrate: chemical compounds of carbon atoms fully hydrated.
  • 'Carbo' = Carbon
  • 'hydrate' = Hydration (water)
• General formula: Cn(H2O)n
  • 1:2:1 ratio of Carbon, Hydrogen, and Oxygen

Monosaccharides

• Monosaccharide = Single Carbohydrate (simple sugar)
• Derived from the Greek word for sugar

Importance in Biological Systems

• Energy Source: Glucose is the main energy source.
  • Glucose is a 6-carbon monosaccharide.
  • Common in context of checking blood glucose levels.
• Structural Role: Cellulose forms plant cell walls.
  • Polysaccharide: several carbohydrates linked together.
• Genetic Material: Ribose (5-carbon sugar) in RNA.
• Carbohydrate names often end in '-ose' (e.g., glucose, cellulose, ribose).

Nomenclature

Prefixes for Carbon Chain Length

• Triose: 3 carbons (e.g., glyceraldehyde)
  • Glyceraldehyde: aldehyde functional group
  • If aldehyde replaced by hydroxyl, it becomes Glycerin
• Tetrose: 4 carbons
• Pentose: 5 carbons
• Hexose: 6 carbons (e.g., glucose)

Functional Groups

• Aldohexose: 6-carbon chain with an aldehyde group (e.g., glucose)
• Ketohexose: 6-carbon chain with a ketone group (e.g., fructose)

Stereochemistry

• Fischer Projection: a way to represent 3D structures in 2D
• Naming based on the highest numbered chiral center
  • Right-side substitution: R-stereochemistry (D configuration)
  • Left-side substitution: L-stereochemistry
• Examples:
  • D-aldohexose: -OH on the right-hand side
  • L-aldohexose: -OH on the left-hand side
  • Glucose is a D-aldohexose

Fischer Projections

• Importance in understanding the absolute configuration
• Recommended resource: Khan Academy video on Fischer Projections

Summary

• Carbohydrates are critical for energy, structure, and genetics.
• Naming involves carbon count, functional groups, and stereochemistry.