MT

16: Carbohydrates and Their Functions

  • Introduction to Glucose

    • Discussion of glucose in linear vs. cyclic form

    • Cyclic Form: Focusing on alpha-D-glucose

  • Chirality and Isomers

    • Linear form of glucose contains 4 chiral carbons

    • Total isomers in glucose: 16 (Calculation: 2^4 = 16)

    • Discussed how to count chiral centers

  • Pyranoses vs. Furanoses

    • Pyranose: Six-membered ring (as in glucose)

    • Furanose: Five-membered ring (as in fructose)

  • Epimers

    • Glucose and galactose are epimers differing at carbon 4

    • To convert glucose to galactose, modify the hydroxyl group on carbon 4

    • Mannose conversion from glucose involves modifications at carbon 2

  • Sugar Acids

    • Glucuronic Acid: Derived from glucose by oxidizing carbon 6

    • Differentiation between aldonic and uronic acids

  • Glycosidic Bonds

    • Defined as the bond between an anomeric carbon and a non-hydroxyl group

    • Example: Lactose is formed by a beta-1,4 glycosidic bond between galactose and glucose

    • Hydrolysis of glycosidic bonds is facilitated by specific enzymes like beta-galactosidase

  • Polysaccharides

    • Amylose and Amylopectin: Both polysaccharides made of glucose

      • Amylose: Unbranched structure, composed of alpha (1→4) linkages

      • Amylopectin: Branched structure with alpha (1→4) and alpha (1→6) linkages

    • Discussion on dietary digestion of amylose versus cellulose

      • Only monosaccharides (like glucose) can be absorbed by the body

      • Example given of cellulose not being digestible due to structural properties

  • Stereochemistry

    • Importance of stereochemistry in digestion and enzyme recognition

    • Example with T-shirt to illustrate the effect of stereochemistry on digestion

  • Chitin

    • Structural polysaccharide made of N-acetylglucosamine

    • Found in exoskeletons of arthropods

  • Glycosaminoglycans

    • Heteropolysaccharides made of two types of sugar derivatives

    • Importance in extracellular matrix and water retention in tissues

  • Proteoglycans

    • Complex structures made of glycosaminoglycans linked to proteins

    • Provide support and hydration in extracellular spaces

  • Peptidoglycans

    • Forms bacterial cell walls

    • Targets for antibiotic treatments due to their unique structure

    • Gram-positive vs. Gram-negative bacteria distinguishing by peptidoglycan structure

  • Glycoproteins

    • Proteins that have carbohydrate chains attached

    • Important for extracellular functions and cellular signaling

    • Sugars linked to either asparagine (N-linked) or serine/threonine (O-linked)

  • Conclusion

    • Overview of the carbohydrate topic and preparedness for upcoming exam on carbohydrates and cellular pathways