Review of Lippincott's Biochemistry Textbook: Chapter 7 - Introduction to Carbohydrates

Overview

• Carbohydrates are abundant organic molecules in nature.
• Serve various functions:
  • Energy source.
  • Energy storage.
  • Part of cell membranes.

Classification of Carbohydrates

• Monosaccharides: Simple sugars, basic building blocks.
  • Classified by carbon atoms:
    • Triose (3 carbons, e.g., glyceralderide).
    • Hexose (6 carbons, e.g., glucose).
  • Classified by carbonyl group:
    • Aldose (contains aldehyde group).
    • Ketose (contains keto group).
• Disaccharides: Two monosaccharides.
• Oligosaccharides: 3 to 10 monosaccharides.
• Polysaccharides: More than 10 monosaccharides, can be hundreds.

Isomers

• Isomers: Same chemical formula, different structures.
  • Examples: fructose, glucose, mannose, galactose.
• Epimers: Differ in configuration around one carbon atom.
  • Example: Glucose and galactose (C4 epimers).
• Enantiomers: Mirror images of each other (L and D forms).
  • Biological processes may be specific to one form.
  • Isomerases: Enzymes that interconvert enantiomers.

Anomers

• Anomers: Formed when a keto group reacts with a hydroxyl group, creating cyclic sugars.
  • Asymmetric carbon forms anomers (alpha or beta).
  • Example: Alpha and beta D-glucopyranose.
• Reducing Sugar: Sugar with a free carbonyl group not in a glycosidic bond.

Glycosidic Bonds

• Formed between monosaccharides via glycosyl transferases.
• N Glycosidic Link: Sugar attached to NH2 group.
• O Glycosidic Link: Sugar attached to OH group.

Carbohydrate Digestion

• Main sites: Mouth and intestinal lumen.
• Glycosidases: Hydrolyze glycosidic bonds.
  • Final product: Monosaccharides absorbed in small intestine.
• Mouth: Salivary alpha-amylase breaks down polysaccharides.
• Intestine: Pancreatic alpha-amylase further breaks down sugars.
  • Enzymes: Iso maltase, maltase, sucrase, lactase.

Absorption of Monosaccharides

• Galactose and Glucose: Active transport via SGLT-1.
• Fructose: Transported by GLUT5.
• All monosaccharides enter circulation via GLUT2.

Disorders

• Lactose Intolerance: Inability to break down lactose due to lack of lactase.
  • Symptoms: Diarrhea, cramps, flatulence.
  • Diagnosis: Oral tolerance tests, breath hydrogen gas measurement.
• Sucrase-Isomaltase Deficiency: Inability to break down sucrose.
  • Treatment: Reduce sucrose intake, enzyme replacement therapy.

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