Chapter 5: Molecular Basis of Inheritance
The chapter "Molecular Basis of Inheritance" is a crucial part of genetics and provides insight into how genetic information is stored, replicated, and expressed. Below is a detailed breakdown of the topics in the chapter to ensure comprehensive understanding.
Introduction
- Definition of genetics and heredity.
- Discovery of DNA as the genetic material.
- Importance of molecular genetics in modern biology.
DNA: The Genetic Material
Historical Perspective
- Griffith's Experiment (1928): Transformation principle.
- Avery, MacLeod, and McCarty (1944): Proved DNA as the transforming principle.
- Hershey and Chase Experiment (1952): Confirmed DNA as genetic material using bacteriophages.
Structure of DNA
- Watson and Crick Model (1953): Double helix structure.
- Components: Sugar-phosphate backbone and nitrogenous bases (Adenine, Thymine, Cytosine, Guanine).
- Base pairing rules: A-T (2 hydrogen bonds), G-C (3 hydrogen bonds).
- Chargaff's Rule: Ratio of purines and pyrimidines.
- Antiparallel strands and complementary base pairing.
Types of DNA
- A-DNA, B-DNA, and Z-DNA: Differences in structure and function.
- Concept of supercoiling.
DNA Packaging
- DNA length vs. size of the nucleus.
- Role of histones and nucleosomes in DNA packaging.
- Chromatin structure: Euchromatin (active) and heterochromatin (inactive).
DNA Replication
- Semiconservative Nature: Experiment by Meselson and Stahl (1958).
- Steps in Replication:
- Unwinding of DNA by helicase.
- Formation of replication fork.
- Role of DNA polymerase in synthesis of new strands.
- Leading and lagging strands: Okazaki fragments.
- Joining by DNA ligase.
- Enzymes involved: Helicase, primase, DNA polymerase, ligase.
Transcription: Synthesis of RNA
- Definition: Conversion of DNA into RNA.
- Types of RNA: mRNA, tRNA, rRNA.
- Steps in Transcription:
- Initiation: Role of RNA polymerase and promoter regions.
- Elongation: Synthesis of RNA strand.
- Termination: Release of RNA transcript.
- Difference between prokaryotic and eukaryotic transcription.
Genetic Code
- Properties: Triplet, non-overlapping, degenerate, universal.
- Codons: Start codon (AUG) and stop codons (UAA, UAG, UGA).
- Experimental proof of the genetic code by Nirenberg and Khorana.
Translation: Protein Synthesis
- Role of ribosomes in translation.
- Steps:
- Activation of amino acids.
- Initiation: Assembly of mRNA, ribosome, and tRNA.
- Elongation: Formation of peptide bonds.
- Termination: Release of polypeptide chain.
- Concept of post-translational modifications.
Regulation of Gene Expression
- Prokaryotic Regulation:
- Operon model: Lac operon (inducible operon).
- Role of structural genes, regulator gene, operator, and promoter.
- Eukaryotic Regulation:
- Epigenetic modifications (DNA methylation, histone acetylation).
- Role of enhancers and silencers.
Human Genome Project (HGP)
- Aim: Sequencing the entire human genome.
- Methodology: Shotgun sequencing and bioinformatics.
- Applications in medicine, agriculture, and evolutionary studies.
DNA Fingerprinting
- Principle: Variability in VNTRs (Variable Number Tandem Repeats).
- Steps in DNA fingerprinting: Extraction, restriction digestion, electrophoresis, hybridization, and autoradiography.
- Applications: Forensics, paternity tests, and biodiversity studies.
RNA World Hypothesis
- Evidence supporting RNA as the first genetic material.
- Role of ribozymes in early evolution.
Molecular Basis of Mutations
- Types: Point mutations, frame-shift mutations.
- Causes: Errors during replication, environmental factors.
- Effects on phenotype and evolutionary significance.
Glossary of Important Terms
- Chromosome, nucleosome, helicase, operon, codon, ribosome, transcription, translation, and more.
Conclusion
The study of the molecular basis of inheritance unravels the complexities of genetic mechanisms. It bridges our understanding of the relationship between genotype and phenotype, paving the way for advancements in genetic engineering, biotechnology, and medical sciences.
