Organic Chemistry Lecture: Carbohydrates

Definition of Carbohydrates

• Molecules composed of carbon, oxygen, and hydrogen.
• Typically follow a formula: carbons, twice as many hydrogens, the same number of oxygens.
• Example: C6H12O6 (Hexoses, e.g., glucose, fructose).

Key Characteristics

• Must have at least three carbons.
• Contains either one aldehyde or one ketone.
• In aliphatic form, all carbons except the one with the aldehyde/ketone must have an OH group.

Simplest Carbohydrates

• Example: Three-carbon carbohydrates with an aldehyde or ketone.
• Line-angle formula indicates carbon presence without angles due to OH groups.
• Can be divided into aldoses (aldehyde) and ketoses (ketone).

Classification by Carbon Atoms

• Trioses (3 carbons), Tetroses (4), Pentoses (5), Hexoses (6), Heptoses (7), Octoses (8), Nonoses (9), etc.
• Naming based on aldehyde or ketone presence and carbon count (e.g., Aldopentose).

Chirality and Configuration

• Chiral centers: Carbons bonded to four different groups.
• D and L nomenclature: refers to OH group position on the highest numbered chiral carbon.
• Example: D-glyceraldehyde (OH on right), L-glyceraldehyde (OH on left).

Glucose Structure and Importance

• D-glucose: Aldohexose with specific OH pattern.
• Importance of D vs. L configurations: Biological function and energy extraction.
• L-glucose: Non-metabolizable, acts as fiber.

Biological Significance

• D-glucose and its derivatives are crucial for energy (ATP production).
• Enzymes recognize D-forms, not L-forms.

Cyclic Forms of Carbohydrates

• Formation of cyclic structures from aliphatic forms to resist oxidation.
• Hemiacetal/hemiketal formation creates stability.
• Alpha and Beta forms based on OH group orientation on anomeric carbon.

Mutarotation

• Dynamic equilibrium between aliphatic and cyclic forms.
• Important for energy regulation and storage.

Disaccharides and Polysaccharides

• Monosaccharides: Single sugar units.
• Disaccharides: Two sugars joined (e.g., maltose, lactose, sucrose).
  • Maltose: Two glucoses with alpha-1,4 linkage.
  • Lactose: Galactose and glucose with beta-1,4 linkage.
  • Sucrose: Glucose and fructose with no reducing ends.
• Polysaccharides: Multiple sugars (e.g., cellulose, amylose, glycogen).
  • Glycogen: Major energy storage form with alpha-1,4 and alpha-1,6 linkages for branching.

Importance in Human Physiology

• Glycogen: Rapid energy release for "fight or flight" response.
• Enzyme specificity for D-forms impacts digestion and energy metabolism.

Summary

• Carbohydrates play essential roles in biological energy storage and retrieval.
• Understanding of structure, configuration, and reactions is crucial for applications in biochemistry and molecular biology.

Further Study

• Practice drawing structures and understanding mechanisms.
• Recognize the difference between reducing and non-reducing sugars.
• Explore carbohydrate chemistry for deeper insights into biological functions.