Carbohydrates Chemistry - 2

Carbohydrates Chemistry - 2

• The lecture is about carbohydrates chemistry, specifically disaccharides, polysaccharides, and glycosaminoglycans (GAGs).
• The professor of the lecture is Dr. Omnia Al-saied Abdullah
• The lecture covers defining disaccharides and differentiating sucrose, lactose, and maltose
• Reduction and non-reduction of disaccharides
• Definition of polysaccharides (starch, glycogen, cellulose)
• Introduction to glycosaminoglycans (GAGs) and their biological roles.
• Clinical importance of heparin as an anticoagulant
• Discussion on non-digestible polysaccharides (e.g., cellulose, inulin) in dietary health

Disaccharides

• Two monosaccharide units are bonded together by a covalent bond called a glycosidic bond.
• The glycosidic bond forms between the hydroxyl group (-OH) of one sugar and the anomeric carbon of the other sugar.
• The specific nature of the glycosidic bond (its orientation and type) varies between different disaccharides.

Sucrose (Table Sugar)

• Composed of glucose and fructose
• α(1→2) glycosidic bond between glucose and fructose with an α-linkage.

Lactose (Milk Sugar)

• Composed of glucose and galactose
• β(1→4) glycosidic bond between glucose and galactose in Beta configuration

Maltose (Malt Sugar)

• Composed of two glucose units.
• α(1→4) glycosidic bond between the two glucose units in alpha configuration

Summary of Bonds

• Sucrose: Glucose (α) + Fructose (β) ,α(1→2) , Non-reducing
• Lactose: Glucose (β) + Galactose (β), β(1→4), Reducing
• Maltose: Glucose (α) + Glucose (α), α(1→4), Reducing

Reducing Power of Disaccharides

• The reducing power of a sugar is its ability to reduce another molecule due to the presence of a free aldehyde or ketone group in its open-chain form.
• Sucrose is a non-reducing sugar.
• Maltose and Lactose are reducing sugars.

Invert Sugar

• Sucrose is hydrolyzed by an acid or enzyme to form an equimolar mixture of glucose and fructose.
• Sucrose has a positive optical rotation, while the resulting mixture has a negative optical rotation, hence the name "invert sugar."
• Invert sugar is used as a sweetening agent in the food industry.

Polysaccharides

• High-molecular-weight carbohydrates composed of long chains of monosaccharide units (more than 10).
• Glycosidic bonds link the monosaccharide units.
• The type of glycosidic bond depends on the configuration of the anomeric carbon.

Classification of Polysaccharides

• Based on Function:
  • Storage Polysaccharides: Store energy (starch in plants, glycogen in animals)
  • Structural Polysaccharides: Provide support (cellulose in plant cell walls, chitin in insect exoskeletons)
• Based on Structure:
  • Homopolysaccharides: Composed of the same type of monosaccharide (starch, glycogen, cellulose, inulin)
  • Heteropolysaccharides: Composed of different types of monosaccharides (glycosaminoglycans).

Starch

• Composed of amylose (linear, α(1→4) bonds) and amylopectin (branched, α(1→4) and α(1→6) bonds).
• Readily digestible by humans, used for energy storage in plants.

Glycogen

• Highly branched polysaccharide of glucose units.
• α(1→4) and α(1→6) bonds.
• Used for energy storage in animals (liver and muscle).

Cellulose

• Linear, unbranched polymer of glucose units with β(1→4) bonds.
• Indigestible by humans, structural component in plant cell walls.

Chitin

• Structural polysaccharide composed of N-acetylglucosamine units linked by β(1→4) bonds.
• Found in exoskeletons of insects and fungi.

Inulin

• Storage polysaccharide composed of fructose units linked by β(2→1) bonds.
• Indigestible by humans but ferments in the gut, promotes beneficial gut bacteria.

Glycosaminoglycans (GAGs)

• Heteropolysaccharides composed of repeating disaccharide units.
• Each disaccharide unit usually has an amino sugar and a uronic acid.
• Highly negatively charged due to sulfate groups.
• Important structural components in connective tissues, blood vessels, and cartilage, acting as lubricants and cushioning.

Hyaluronic Acid

• Major GAG
• Non-sulfated
• High molecular weight giving a high capacity to retain water.
• Functions include lubrication, hydration, and structural support.

Heparin

• Highly sulfated GAG
• Anticoagulant, prevents blood clot formation by activating antithrombin III
• Used to treat thromboembolic disorders, such as heart attacks, strokes, and pulmonary embolisms.

Formative Questions

• Questions regarding different carbohydrates and their properties.

This quiz covers the chemistry of carbohydrates with a focus on disaccharides, polysaccharides, and glycosaminoglycans. It includes topics such as the definition and differentiation of common disaccharides, the clinical importance of heparin, and the health impacts of non-digestible polysaccharides. Perfect for students studying under Dr. Omnia Al-saied Abdullah.