HBG 102: Disaccharides & Sugar Derivatives

Course Information

• Course: HBG 102
• Level: 1
• Semester: 1
• Subject: Carbohydrates Chemistry
• Topic: Disaccharides & Sugar Derivatives

Sugar Derivatives

• Types and examples of each type are covered
• Structures of various sugar derivatives are illustrated
• Functions are described

Disaccharides

• Definitions, examples, and significance of disaccharides are explained

Learning Outcomes

• Students will be able to recognize sugar derivatives
• Students will be able to correlate the structure of sugar derivatives to their function
• Students will be able to apply their knowledge to clinical situations
• Students will be able to define and classify disaccharides
• Students will be able to recognize the significance of different types of disaccharides

Case Scenario (Clinical Correlate)

• Samir, a 50-year-old patient, presented with a 2-week history of polyuria (frequent urination), polydipsia (excessive thirst), polyphagia (excessive hunger), 20-pound weight loss, and blurred vision.
• A urinalysis indicated excess glucose.
• His initial blood glucose level was 340 mg/dL.

Learning Objectives (LOs)

• LO 1: Recognizing the monosaccharides derivatives
• LO 2: Correlating structure of various types of monosaccharides derivative to function
• LO 4: Correlation of knowledge to a clinical situation.
• LO 1: Defining and classifying disaccharides
• LO 2: Recognizing the structure of different types of disaccharides and their significance

Sugar Acids

• Definition: Oxidation products of monosaccharides
• Examples:
  • Aldonic acids
  • Uronic acids
  • Aldaric acids
  • L-ascorbic acid (Vitamin C)

Sugar Alcohols (Alditols)

• Definition: Products of reduction of monosaccharides
• Examples:
  • D-glucitol (or D-sorbitol) from D-glucose
  • D-mannitol from D-mannose
  • D-sorbitol or D-mannitol from D-fructose
  • D-galactitol or D-dulcitol from D-galactose
  • D-ribitol from D-ribose
  • D-xylitol from D-xylose

Deoxy-sugars

• Definition: Monosaccharides with one oxygen atom missing (one OH group replaced by H)
• Example: 2-deoxy-D-ribose is a constituent of DNA

Amino-Sugars

• Hydroxyl group replaced by an amino group at the C-2 position
• Examples: D-glucosamine, D-galactosamine
• Found in glycosaminoglycans and glycoproteins

Amino-sugar Acids

• Definition: Condensation products of amino sugars and some acids
• Example: Neuraminic acid (mannosamine + pyruvic acid) is found in neural tissues

Homodisaccharides

• Maltose: Formed from two α-D-glucose units linked by an α (1→4) glycosidic bond. Produced by the actions of amylase enzymes on starch. Hydrolyzed by maltase to produce 2 glucose molecules.
• Isomaltose: Formed from two α-D-glucose units linked by an α (1→6) glycosidic bond. A reducing sugar, obtained by hydrolysis of some polysaccharides, such as dextran.
• Cellobiose: Formed from two β-D-glucose units linked by a β (1→4) glycosidic bond. Obtained by acid hydrolysis of cellulose.

Heterodisaccharides

• Sucrose: Formed from α-glucose and β-fructose linked by an α(1→2) glycosidic bond. It is non-reducing. Hydrolysis catalyzed by sucrase.
• Lactose: Formed from β-galactose and β-glucose via a β (1→4) link with a free anomeric carbon. It is a reducing sugar. Found in milk; its hydrolysis is catalyzed by the enzyme lactase.

Clinical Correlates (Lactose Intolerance)

• Low levels of lactase lead to undigested lactose. Bacteria ferment this in the colon, generating CO2, H2, and organic acids.
• These products cause painful digestive upsets (lactose intolerance)

Case Scenario (Clinical Correlate - 2)

• Samira, a 65-year-old woman presenting with numbness in her toes and impaired vision.
• Blood Glucose level of 384 mg/dL.

Other

• Discussion and Feedback (10 minutes)