Description

• Definition: The molecular basis of inheritance refers to the mechanisms through which genetic information is passed from one generation to the next at the molecular level.
• Genetic Material: DNA (Deoxyribonucleic Acid) is the primary genetic material in most organisms.

2. Structure of DNA

• Double Helix Model: Proposed by Watson and Crick.
• Components:
  • Nucleotides: Basic units of DNA, consisting of a phosphate group, a deoxyribose sugar, and a nitrogenous base.
  • Nitrogenous Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
  • Base Pairing: A with T (two hydrogen bonds), C with G (three hydrogen bonds).
  • Backbone: Alternating sugar and phosphate groups.

3. DNA Replication

• Semi-Conservative Replication: Each new DNA molecule consists of one old and one new strand.
• Key Enzymes:
  • Helicase: Unwinds the DNA double helix.
  • DNA Polymerase: Adds new nucleotides to the growing strand.
  • Primase: Synthesizes RNA primer.
  • Ligase: Seals the gaps between Okazaki fragments on the lagging strand.

4. Transcription

• Definition: The process of synthesizing RNA from a DNA template.
• Types of RNA:
  • mRNA (Messenger RNA): Carries genetic information from DNA to the ribosome.
  • tRNA (Transfer RNA): Brings amino acids to the ribosome.
  • rRNA (Ribosomal RNA): Forms the core of the ribosome’s structure.
• Steps of Transcription:
  • Initiation: RNA polymerase binds to the promoter region.
  • Elongation: RNA polymerase synthesizes RNA.
  • Termination: RNA polymerase reaches a terminator sequence and releases the RNA.

5. Genetic Code

• Triplet Code: Each codon (set of three nucleotides) codes for one amino acid.
• Characteristics:
  • Degenerate: Multiple codons can code for the same amino acid.
  • Universal: Same codons specify the same amino acids in nearly all organisms.
  • Non-Overlapping and Commaless: Codons are read one after another without overlapping and without gaps.
  • Translation
  • Definition: The process of synthesizing proteins from mRNA.
  • Steps of Translation:
  • Initiation: The small ribosomal subunit binds to the mRNA.
  • Elongation: tRNA brings amino acids to the ribosome, and peptide bonds form between amino acids.
  • Termination: The ribosome reaches a stop codon, and the polypeptide is released.
  • 7. Regulation of Gene Expression
  • Prokaryotic Regulation: Operon model (e.g., lac operon in E. coli).
  • Eukaryotic Regulation:
  • Transcriptional Control: Involves enhancers, silencers, and transcription factors.
  • Post-Transcriptional Control: mRNA splicing, editing, and degradation.
  • Translational Control: Involves the initiation of translation and mRNA stability.
  • Post-Translational Control: Protein modification and degradation.
  • 8. Mutations
  • Definition: Changes in the DNA sequence that affect genetic information.
  • Types:
  • Point Mutations: Single nucleotide changes (e.g., substitutions, insertions, deletions).
  • Frameshift Mutations: Insertions or deletions that alter the reading frame.
  • Causes:
  • Spontaneous Mutations: Errors in DNA replication.
  • Induced Mutations: Caused by mutagens like chemicals and radiation.
  • 9. DNA Repair Mechanisms
  • Direct Repair: Reverses DNA damage directly.
  • Excision Repair: Removes damaged DNA and replaces it with the correct sequence.
  • Base Excision Repair (BER)
  • Nucleotide Excision Repair (NER)
  • Mismatch Repair: Corrects errors missed by DNA polymerase during replication.
  • 10. Recombinant DNA Technology
  • Definition: Techniques used to manipulate DNA for research and practical applications.
  • Steps:
  • Isolation of DNA
  • Cutting DNA using Restriction Enzymes
  • Inserting DNA into Vectors
  • Introduction of Recombinant DNA into Host Cells
  • Selection and Screening of Recombinants