Quick Revision Notes: Biomolecules

Class: 12 Chemistry (MP Board)

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### 1. Introduction to Biomolecules

Biomolecules are complex organic molecules that form the basis of life, building up living systems and responsible for their growth, maintenance, and metabolic processes.

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### 2. Carbohydrates

Optically active polyhydroxy aldehydes (-CHO) or polyhydroxy ketones (>C=O) or compounds that yield these on hydrolysis.

Classification of Carbohydrates:

1. Monosaccharides: Cannot be hydrolysed further into smaller units (e.g., Glucose, Fructose, Ribose).
2. Oligosaccharides: Yield 2 to 10 monosaccharide units on hydrolysis (e.g., Sucrose, Lactose, Maltose).
3. Polysaccharides: Yield a large number of monosaccharide units on hydrolysis (e.g., Starch, Cellulose, Glycogen).

Reducing vs Non-reducing Sugars:

• Reducing Sugars: Carbohydrates that reduce Fehling's solution and Tollen's reagent (e.g., All monosaccharides, Maltose, Lactose).
• Non-reducing Sugars: Do not reduce Fehling's solution or Tollen's reagent (e.g., Sucrose).

Important Structures:

• Glucose (Aldohexose): CH2OH-(CHOH)4-CHO
• Fructose (Ketohexose): CH2OH-CO-(CHOH)3-CH2OH
• Glycosidic Linkage: The oxide linkage formed by the loss of a water molecule between two monosaccharide units.

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### 3. Proteins

Proteins are high molecular weight polymers of $\alpha$-amino acids linked together by peptide bonds.

Amino Acids:

• General Formula: R-CH(NH2)-COOH
• Essential Amino Acids: Cannot be synthesized in the body; must be obtained through diet (e.g., Valine, Leucine).
• Non-essential Amino Acids: Synthesized by the body (e.g., Glycine, Alanine).
• Zwitter Ion: Dipolar ion formed by the transfer of a proton from the carboxylic group to the amino group within an amino acid (H3N+-R-CH-COO-).

Peptide Bond and Protein Structures:

• Peptide Linkage: -CO-NH- bond formed between two amino acids.
• Levels of Protein Structure:
  1. Primary Structure: Sequence of amino acids.
  2. Secondary Structure: Folding or coiling of polypeptide chain ($\alpha$-helix and $\beta$-pleated sheet).
  3. Tertiary Structure: 3D folding giving stable globular or fibrous shapes.
  4. Quaternary Structure: Spatial arrangement of multiple polypeptide chains (subunits).
• Denaturation of Protein: Loss of biological activity of proteins due to physical (temperature) or chemical (pH change) stress (e.g., coagulation of egg white on boiling).

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### 4. Nucleic Acids

Biomolecules responsible for the transmission of hereditary characteristics and protein synthesis.

Components of Nucleic Acids:

1. Pentose Sugar: $\beta$-D-ribose (in RNA) or 2-deoxy-$\beta$-D-ribose (in DNA).
2. Nitrogenous Bases:
   • Purines: Adenine (A) and Guanine (G)
   • Pyrimidines: Cytosine (C), Thymine (T - only in DNA), and Uracil (U - only in RNA)
3. Phosphoric Acid: (H3PO4) responsible for the backbone of nucleic acids.

Nucleoside vs Nucleotide:

• Nucleoside: Base + Sugar
• Nucleotide: Base + Sugar + Phosphate group (Building blocks of nucleic acids linked by phosphodiester bonds).

Differences between DNA and RNA:

Feature	DNA (Deoxyribonucleic Acid)	RNA (Ribonucleic Acid)
Sugar	2-Deoxy-D-ribose	D-Ribose
Bases	A, G, C, T	A, G, C, U
Structure	Double helix	Single stranded
Function	Hereditary transfer	Protein synthesis

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### 5. Vitamins

Organic compounds required in small amounts for normal health, growth, and metabolism. Cannot be synthesized by the body.

Classification:

1. Fat-soluble Vitamins: Soluble in fat and oils, stored in liver and adipose tissue.

   • Vitamin A: Retinol (Deficiency: Xerophthalmia, Night blindness)
   • Vitamin D: Ergocalciferol / Cholecalciferol (Deficiency: Rickets, Osteomalacia)
   • Vitamin E: Tocopherol (Deficiency: Increased fragility of RBCs)
   • Vitamin K: Phylloquinone (Deficiency: Non-clotting of blood)

2. Water-soluble Vitamins: Soluble in water, must be supplied regularly in diet (except Vitamin B12).

   • Vitamin B1: Thiamine (Deficiency: Beriberi)
   • Vitamin B2: Riboflavin (Deficiency: Cheilosis, fissuring at corners of mouth)
   • Vitamin B12: Cyanocobalamine (Deficiency: Pernicious anaemia)
   • Vitamin C: Ascorbic acid (Deficiency: Scurvy - bleeding gums)