Class 12 Biology – Carbohydrates and Proteins

1. Carbohydrates

Definition

• Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen.

• They serve as a primary energy source and have structural roles in living organisms.

Classification

1. Monosaccharides (Simple sugars)

   • Single sugar units.

   • Examples: Glucose, Fructose, Galactose.

   • Features: Soluble in water, sweet taste, rapid energy source.

2. Disaccharides

   • Composed of two monosaccharide units.

   • Examples: Sucrose, Lactose, Maltose.

   • Features: Soluble in water, transport form of sugar in plants.

3. Polysaccharides

   • Long chains of monosaccharides.

   • Examples: Starch, Glycogen, Cellulose, Chitin.

   • Features: Insoluble in water, storage or structural roles.

Functions

• Energy source: Glucose provides immediate energy.

• Energy storage: Starch in plants, glycogen in animals.

• Structural support: Cellulose in plant cell walls, chitin in exoskeletons.

2. Proteins

Definition

• Proteins are polymers of amino acids, containing carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

• They are essential for structure, function, and regulation of tissues and organs.

Structure of Proteins

1. Primary Structure: Sequence of amino acids.

2. Secondary Structure: Folding into alpha-helix or beta-pleated sheets.

3. Tertiary Structure: 3D folding of the polypeptide chain.

4. Quaternary Structure: Combination of multiple polypeptide chains.

Types of Proteins

• Fibrous Proteins: Provide structural support. Example: Keratin, Collagen.

• Globular Proteins: Perform functional roles like enzymes, transport, hormones. Example: Hemoglobin, Insulin.

Functions

• Structural: Collagen, keratin.

• Enzymatic: Catalysts for biological reactions.

• Transport: Hemoglobin transports oxygen.

• Defense: Antibodies protect against infections.

• Hormonal: Insulin regulates blood sugar.

3. Key Points to Remember

• Carbohydrates: Energy source, storage, and structural role.

• Proteins: Structural and functional roles, made of amino acids.

• Polysaccharides: Starch (plants), Glycogen (animals), Cellulose (plants).

• Protein structures: Primary → Secondary → Tertiary → Quaternary.

• Both are essential biomolecules for life processes, growth, and metabolism.