Biology Student Book 1.pdf 3

2 CARBOHYDRATES

1.1 Introduction to Carbohydrates

  • Carbohydrates are essential biological molecules composed primarily of carbon, hydrogen, and oxygen atoms.

  • They serve as a primary energy source for living organisms and play critical roles in structure (e.g., cell walls) and energy storage.

  • Understanding carbohydrates is fundamental to the study of biochemistry and biology.

1.2 Classification of Carbohydrates

1.2.1 Monosaccharides

  • Definition: Monosaccharides are the simplest form of carbohydrates, consisting of single sugar units.

  • General Formula: Generally represented as (CH₂O)n, where n typically ranges from 3 to 7 (e.g., Glucose C₆H₁₂O₆).

  • Types:

    • Triose: 3 carbon atoms (e.g., glyceraldehyde).

    • Pentose: 5 carbon atoms (e.g., ribose and deoxyribose).

    • Hexose: 6 carbon atoms (e.g., glucose, fructose, galactose).

  • Properties: Monosaccharides are sweet in taste and readily soluble in water.

1.2.2 Disaccharides

  • Definition: Disaccharides consist of two monosaccharides linked together.

  • Formation: Formed through condensation reactions, which result in a glycosidic bond and the release of one water molecule.

  • Examples:

    • Sucrose: Glucose + Fructose

    • Maltose: Glucose + Glucose

    • Lactose: Glucose + Galactose

  • Testing: Benedict’s test is used to identify reducing sugars (except non-reducing sugars like sucrose), with a color change indicating the presence of reducing sugars.

1.2.3 Polysaccharides

  • Definition: Polysaccharides are large carbohydrate molecules composed of long chains of monosaccharide units.

  • Types:

    • Starch: A storage polysaccharide in plants with two forms:

      • Amylose: Unbranched chains.

      • Amylopectin: Branched chains.

    • Glycogen: An energy storage polysaccharide in animals, similar to amylopectin but more highly branched for rapid energy release.

  • Characteristics: Polysaccharides are not sweet-tasting, less soluble in water, and serve primarily for energy storage.

1.3 Formation and Hydrolysis of Carbohydrates

1.3.1 Glycosidic Bonds

  • Definition: A glycosidic bond is a covalent bond formed between two monosaccharides during a condensation reaction.

  • Types of Bonds:

    • 1,4-glycosidic bond: connects the first carbon of one monosaccharide to the fourth carbon of another.

    • 1,6-glycosidic bond: connects the first carbon of one monosaccharide to the sixth carbon of another.

  • Breaking Bonds: Glycosidic bonds can be cleaved by hydrolysis reactions, which add water to break the bond and release monosaccharide units.

1.4 Energy and Biological Importance

  • Carbohydrates are critical for energy, as they can be readily converted into ATP during cellular respiration.

  • Monosaccharides provide quick energy, while polysaccharides (like starch and glycogen) serve as more stable storage forms, releasing glucose as needed during periods of activity.

  • Hydrolysis Importance: This reaction is vital in the digestive process, allowing organisms to utilize the carbohydrates consumed in their diets effectively.