Carbohydrates part1 - Copy (1).pptx (1)

CARBOHYDRATES

Learning Objectives (Part 1)

  • Describe the major structural features and functions of carbohydrates.

  • Distinguish between aldoses and ketoses.

  • Draw the linear and Haworth structures of glucose and fructose as examples of aldoses and ketoses.

  • Describe anomerisation in simple sugars.

What are Carbohydrates?

  • Carbohydrates are one of the three main nutrients required for human survival, along with fats and proteins.

  • Common sources: bread, cereals, potatoes, and rice.

  • Function: Primarily used as an energy source and a structural component.

Main Functions of Carbohydrates

  • Energy source: Example: Glucose

  • Structural elements: Example: Cellulose in plants, chitin in insects.

  • Precursors in the production of other biomolecules: Includes amino acids, lipids, purines, and pyrimidines.

Main Features of Monomeric Carbohydrates (Monosaccharides)

  1. Composition: Contain carbon (C), hydrogen (H), and oxygen (O).

    • Breakdown of the term: Carbo (carbon) + hydrate (H2O).

    • Commonly referred to as "saccharides".

  2. Formula for Monosaccharides: (CH2O)n where n is 3 or greater. The number of C = number of H2O

    • Example: Formula for glucose is C6H12O6.

Classification of Carbohydrates

  • Classified according to the number of simple sugars they contain:

    • Monosaccharides: Contains 1 sugar unit (e.g., glucose, galactose, fructose).

    • Disaccharides: Contains 2 monosaccharide units (e.g., sucrose, lactose, maltose).

    • Oligosaccharides: Contains 2 to 10 sugar units (e.g., fruco-oligosaccharides found in vegetables).

    • Polysaccharides: Contains more than 10 sugar units (e.g., starch, glycogen, chitin, cellulose).

Test Yourself: Simple Sugars

  1. Fill in the formula:

    • C? H12 O?

    • C4 H? O?

    • C? H? O3

  2. Fill in the formula with answers:

    • C6 H12 O6 (Glucose)

    • C4 H8 O4 (potential candidate)

    • C3 H6 O3 (potential candidate)

Test Yourself: Structure of Maltose

  • Maltose is a Disaccharide (B).

Starch Structure and Function

  • Starch contains chains of sugar residues and is characterized as a Polysaccharide (D).

Monosaccharides - Aldose and Ketose

  • Aldoses: Monosaccharides containing an aldehyde group at one end.

  • Ketoses: Monosaccharides containing a ketone group in the middle.

Naming the Sugar Structures

  1. Determine if the monosaccharide contains an aldehyde or ketone group.

  2. Count the number of carbon atoms to identify the class (e.g., triose, tetrose).

Common Types of Monosaccharides

  • D-sugars: Sugars with OH on the right-most carbon of the open chain, mostly found in nature.

  • L-sugars: Sugars with OH on the left-most carbon.

Cyclic Structures (Haworth Structures)

  • Sugars with four or more carbons naturally exist in cyclic forms, which are more stable.

  • Haworth projections are used to depict cyclic forms derived from linear Fischer projections.

Anomers

  • During cyclization, the configuration at the anomeric carbon (C1) can be either alpha (α) or beta (β).

  • The α-anomer has the OH group below the ring, while the β-anomer has it above.

Formation of Disaccharides and Polysaccharides

  • Glycosidic Linkages: Formed when the hydroxyl (-OH) group of one monosaccharide reacts with the -OH group of another.

    • This reaction removes water (condensation reaction).

  • Common disaccharides:

    • Maltose: Formed by two glucose molecules linked by an α-(1,4) glycosidic bond.

    • Sucrose: Formed between one glucose and one fructose linked by an α-(1,β-2) glycosidic bond.

    • Lactose: Formed between glucose and galactose via a β-(1,4) glycosidic bond.

Polysaccharides

  • Glycogen: Stored glucose in animals, primarily in the liver and muscle cells, linked by α-(1,4) glycosidic linkages with branching from α-(1,6) linkages.

  • Starch: Exists in plants, made of amylose (unbranched) and amylopectin (branched), both formed with α-(1,4) linkages.