Lecture on Monosaccharides

Monosaccharides

• Definition: The basic building blocks of carbohydrates; single-unit sugars that combine to form larger carbohydrates.
• Structure: Represented by a bubble diagram, indicating they are small, simple molecules.

Tyndall Effect Experiment

• Purpose: To determine if monosaccharides scatter light when dissolved in water.
• Observation: When light passes through a solution of monosaccharides, it does not scatter, indicating their small size.

Key Monosaccharides in Biology

• Five Important Monosaccharides:
  1. D-Glucose
  2. D-Fructose
  3. D-Galactose
  4. D-Ribose
  5. D-Deoxyribose

D-Glucose

• Type: Aldohexose (contains an aldehyde group).
• Carbon Count: Six carbons (C₆H₁₂O₆).
• Alternate Name: Dextrose; important for energy, often referred to as blood sugar.
• Function: Source of energy for cells, derived from dietary carbohydrates.

D-Fructose

• Type: Ketohexose (contains a ketone group).
• Carbon Count: Six carbons (C₆H₁₂O₆).
• Alternate Names: Levulose, fruit sugar; found in fruits and honey.
• Health Controversy: Presence in high fructose corn syrup raises dietary health discussions.

D-Galactose

• Type: Aldohexose.
• Carbon Count: Six carbons (C₆H₁₂O₆).
• Function: Component of lactose (milk sugar); produced in mammary glands.
• Isomer Relationship: Diastereomer of D-glucose (differing at the fourth carbon).

D-Ribose and D-Deoxyribose

• Type: Aldo-pentoses (five carbons).
• Function: Structural components of nucleic acids (RNA and DNA).
  • D-Ribose: Contains five oxygen atoms.
  • D-Deoxyribose: Missing one oxygen due to the prefix "deoxy."

Physical Properties of Monosaccharides

• Solubility: Highly soluble in water due to the presence of numerous hydroxy (OH) groups, which enable hydrogen bonding.
• Boiling and Melting Points: High boiling and melting points due to hydrogen bonding, leading them to be solid at room temperature.
• Intermolecular Forces: Strong intermolecular forces (stickiness) due to extensive hydrogen bonding.

Biological Relevance

• Functionality of D-Glucose: Highly soluble in blood, allowing efficient transport as an energy source to cells. This solubility is essential due to the aquatic environment of blood.
• Chemical Structure and Biological Function: The polarity of monosaccharides is pivotal for their biological roles, especially in energy transport.

Sweetness of Monosaccharides

• Definition of Sugar: A carbohydrate with a sweet taste.
• Sweetness Comparisons:
  • Different monosaccharides and disaccharides have varying sweetness scores.
  • D-Fructose: Notably sweeter than sucrose; has a sweetness score of 1.73 (compared to sucrose's 1.00).
  • Function in Products: The high sweetness of fructose leads to its use in sweeteners, allowing manufacturers to use smaller quantities for desired sweetness.
• Polysaccharides: Generally tasteless, such as starch in potatoes or cellulose in lettuce, unlike the sweet tastes of monosaccharides and disaccharides.