Molecular Basis of Inheritance

Overview

• Total DNA length: ~2.2 meters in each cell.
• Genes typically ~3000 base pairs long.
• Lecture by Dr. Vipin Kumar Sharma on molecular inheritance.
• Recommended detailed study & note-taking for effective revision.
• Principals of inheritance discussed in previous chapters.

Key Concepts

DNA and RNA as Genetic Materials

• DNA: Deoxyribonucleic Acid; RNA: Ribonucleic Acid
• DNA is the genetic material in most organisms; RNA in some viruses.
• Both DNA & RNA are nucleic acids formed by polynucleotides.

Molecular Structure

• Nucleic Acids: Formed by nucleotides, not nucleosides.
• DNA/RNA Structure: Nitrogenous bases, sugars, and phosphate groups.
• DNA: Double-stranded helix; RNA: Single-stranded.
• Purines (Adenine, Guanine) & Pyrimidines (Cytosine, Thymine in DNA; Uracil in RNA).

DNA Double Helix

• Discovered by Watson and Crick using Franklin’s X-ray diffraction data.
• Base pairing: A-T (2 H-bonds), C-G (3 H-bonds).
• Total genome length in humans: 3.3 billion base pairs.

DNA Packaging

• DNA wraps around histone proteins forming nucleosomes (beads on a string model).
• Further packaging required during cell division using non-histone proteins.

Experimental Proofs of DNA as Genetic Material

1. Griffith’s Transformation Principle (1928)
   • R and S strains of Streptococcus pneumoniae; live R strain + heat-killed S strain could transform R to S.
2. Avery, MacLeod, and McCarty
   • Proved DNA is the transforming principle through selective enzyme degradations.