Carbohydrate Chemistry and Polysaccharides Notes

Basics Carbohydrate Chemistry and Polysaccharides and Clinical Importance

Learning Outcomes

  • List various disaccharides and their clinical importance.

  • List the physiological functions of polysaccharides

  • Justify the clinical importance of various polysaccharides.

Disaccharides

  • Composed of two monosaccharide units bound together by a covalent bond (alpha or beta) known as a glycosidic linkage formed via a dehydration reaction.

  • Alpha bonds are digestible by the human body due to the presence of specific enzymes.

  • Beta bonds are not digestible because of the absence of specific enzymes.

  • Examples: Maltose, Lactose, Cellobiose, Isomaltose.

Maltose

  • Made up of two α-glucose residues.

  • Is an intermediary in acid and enzyme hydrolysis of starch.

  • Action of specific enzyme maltase yields 2 glucose residues.

  • Has reducing properties and forms osazones, which has a characteristic sunflower appearance.

Maltosazone

  • Sunflower-shaped crystals.

Lactose

  • Made up of Beta-glucose and Galactose residues.

  • Is a milk sugar.

  • Action of specific enzyme lactase yields glucose and Galactose residues.

  • Has reducing properties and forms osazones with a characteristic Powder puff or hedgehog appearance.

Lactosazone

  • Powderpuff or hedgehog-shaped crystals.

Lactose Intolerance

  • Deficiency of enzyme lactase.

  • Symptoms: Nausea, Vomiting, Diarrhea, Gas and bloating, Pain (abdomen).

  • Normal Digestion: Lactose + Lactase Enzyme in GI Tract yields Glucose + Galactose.

  • If no lactase is available: Lactose + H2O results in Diarrhea.

Lactulose

  • Is a non-absorbable synthetic disaccharide.

  • Made up of galactose and fructose units.

  • Used in the treatment of constipation and hepatic encephalopathy.

Sucrose

  • Made up of One alpha-glucose and one beta-fructose residue.

  • Is an ordinary table sugar.

  • Action of specific enzyme sucrase yields glucose and fructose residues.

  • It does not have reducing properties and cannot form osazones.

Invert Sugar

  • Called invert sugar because sucrose is dextrorotatory, but its hydrolytic products are levorotatory.

  • Hydrolytic products invert the rotation, so the resulting mixtures of glucose and fructose are called invert sugar.

  • Honey is largely invert sugar, and the presence of fructose accounts for its greater sweetness.

Oligosaccharides

  • Formed when more than three to ten sugar units combine.

  • Examples:

    • Raffinose: Glucose + Galactose + Glucose

    • Stachyose: 2 Moles of galactose + Glucose + Fructose

  • Mostly of plant origin.

  • "Oligo" means few.

Polysaccharides

  • Contain more than ten monosaccharide units.

  • Two types:

    1. Homo polysaccharides (Starch, glycogen etc.)

    2. Hetero polysaccharides (GAGS)

Starch

  • Carbohydrate reserve of plants.

  • Important dietary source for humans.

  • High content is present in cereals, roots, tubers.

  • Made up of multiple units of alpha-D Glucose.

  • Two components:

    1. Amylose: water-soluble, unbranched, gives a blue color with iodine.

    2. Amylopectin: Water-insoluble, branched, gives a violet color with iodine.

  • Starch \xrightarrow{Amylase} dextrin’s \rightarrow Maltose + Glucose

Structure of Starch

  • \alpha-Amylose and Amylopectin structures showing glucose units and glycosidic bonds.

  • Amylopectin has \alpha(1\rightarrow6) branches.

Cellulose

  • Exclusively present in the plant kingdom.

  • Totally absent in the animal body.

  • Made up of beta-D glucose units linked by beta glycosidic linkages.

  • Cannot be digested in humans.

  • Major constituent of dietary fiber.

Role of Cellulose

  • Role in diabetes:

    • Blood Sugar Control: Cellulose slows the absorption of glucose, leading to a gradual rise in blood sugar levels.

    • Insulin Sensitivity: Increased fiber intake is associated with improved insulin sensitivity.

  • Role in lipid profile:

    • Cholesterol Reduction: Binds to bile acids in the intestine, reducing overall cholesterol levels.

    • Lower LDL Levels: Regular intake is linked to reduced levels of low-density lipoprotein (LDL) cholesterol.

  • Role in constipation:

    • Increasing Stool Bulk: Adds bulk to the stool, stimulating bowel movements.

    • Promoting Regularity: Aids in softening the stool and enhancing waste movement, reducing constipation.

Glycogen

  • Animal reserve of the body.

  • Present in high concentration in the liver, muscle, and brain.

  • Similar to Amylopectin, made up of repeated units of alpha-D-Glucose linked by glycosidic linkages.

Structure of Glycogen

  • Glycogen structure showing glucose units and branches.

Inulin

  • Polymer of fructose.

  • Present in garlic, onion, dahlia bulbs, etc.

  • Low molecular weight, easily soluble in water.

  • Not utilized by the body.

  • Used for assessing kidney function through GFR.

Dextrans

  • Polymer of Alpha-D glucose linked by glycosidic linkages.

  • Used as a plasma expander.

  • When given I.V in cases of blood loss (Hemorrhage), it increases the blood volume.

Chitin

  • Composed of N-acetyl-D-glucosamine.

  • Found in the exoskeleton of some invertebrates.

Plasma Expanders

  • Substances used to increase the plasma volume in the bloodstream, primarily in cases of significant blood loss or hypovolemia.

  • Types:

    • Crystalloids:

      • Examples: Saline, Ringer's lactate

      • Characteristics: Contain small molecules that can move freely across vascular membranes.

    • Colloids:

      • Examples: Albumin, Dextran, Hydroxyethyl starch (HES), Gelatins

      • Characteristics: Contain larger molecules that remain in the vascular space, increasing oncotic pressure and drawing fluid into the bloodstream.