Molecular Biology Notes

MOLECULAR BIOLOGY OVERVIEW

  • Prokaryotic Cell Genome:

    • Circular bacterial DNA associated with protein scaffolds.
    • Features of prokaryotic genome from a DNA structural perspective:
    • Circles double-stranded DNA
    • Supercoiled structure.

  • Eukaryotic Cell Genome:

    • DNA structure as follows:
    • DNA double helix diameter: 2 nm
    • Nucleosomes (10 nm structure)
    • Chromatin fibril (30 nm)
    • Extended chromosome (300 nm)
    • Fully condensed chromosome (1400 nm).

CELL CYCLE PHASES

  • Interphase:

    • G₁ Phase: Cell growth and metabolism; organelle duplication.
    • S Phase: DNA replication and chromosome duplication.
    • G₂ Phase: Growth and preparation for mitosis.

  • Mitosis (M Phase):

    • Progression through the stages:
    • Prophase → Prometaphase → Metaphase → Anaphase → Telophase
    • Followed by Cytokinesis.

DNA REPLICATION MECHANISMS

  • Proposed Models of Replication:
    • 1. Semiconservative Replication: Most accepted model.
    • 2. Conservative Replication.
    • 3. Dispersive Replication.
Semiconservative DNA Replication
  • Each strand serves as a template; following generations reflect this process.
    • Parental DNA separates and each strand pairs with a new strand.
Replication in Bacteria
  • Key Features:
    • Origin: Initiates at oriC.
    • Bidirectional replication: Two replication forks.
    • Involves enzymes such as:
    • Topoisomerases (e.g., DNA gyrase)
    • Helicase
    • Single-stranded binding proteins (SSB)
    • DNA polymerases.
Eukaryotic DNA Replication
  • Features of replication in eukaryotic cells:
    • Replicons which allow for multiple origins of replication across the genome.
    • DNA Polymerases: Five types in eukaryotes, each with specific functions:
    • α: Associated with primase for Okazaki fragments.
    • β: Functions in DNA repair.
    • γ: Replicates mitochondrial DNA.
    • δ: Extends primers in the lagging strand.
    • ε: Assists leading strand replication.

MUTATIONS

  • Definition: A permanent, heritable change in DNA sequence.
    • Can affect mRNA and protein products, leading to various cellular properties like disease, morphology changes, and antibiotic susceptibility.
Types of Mutations
  • Point mutations:
    • Transition: Base pair replacement within purine or pyrimidine.
    • Transversion: Replacement between purine and pyrimidine pairs.
Effects on Proteins
  • Silent Mutations: No change in amino acid sequence.
  • Missense Mutations: Altered amino acid sequence, potential functional impact.
  • Nonsense Mutations: Create a stop codon, leading to truncated proteins.
  • Frameshift Mutations: Result from base insertions/deletions, altering reading frame.
  • Large Segment Deletions: May arise from unequal crossing over during meiosis.
DNA REPAIR MECHANISMS
  • Importance to maintain genetic integrity due to susceptibility to environmental damage.
  • Types of DNA Repair:
    • Nucleotide Excision Repair (NER): Recognizes and repairs bulky lesions.
    • Base Excision Repair (BER): Fixes small, non-helix-distorting lesions.
    • Mismatch Repair (MMR): Corrects replication errors.
    • Double-Strand Break Repair: Includes Non-Homologous End Joining and Homologous Recombination.

TRANSCRIPTION

  • Process: Converts DNA into mRNA.
    • Begins when RNA polymerase binds to the promoter region, unwinding the DNA.
    • Involves initiation factors and the formation of a transcription bubble.
Eukaryotic vs Prokaryotic Transcription
  • Eukaryotic transcription necessitates additional transcription factors for the assembly of RNA polymerases.
  • Post-transcriptional modifications include 5' capping, polyadenylation, and splicing of introns.

POST-TRANSCRIPTIONAL MODIFICATIONS

  • Ensures the maturation of mRNA from primary transcripts:
    • 5' Capping: Involves the addition of a methylated guanine cap.
    • Polyadenylation: Addition of poly(A) tail for stability and nuclear export.
    • RNA Splicing: Removal of introns with precise ligation of exons.

TRANSLATION

  • Stages of Translation:
    • Initiation, elongation, and termination processes lead to protein synthesis.
  • Ribosomal structures: 70S in prokaryotes and 80S in eukaryotes; differ in complex nature and specific components.
  • Key role of tRNA in serving amino acids and facilitating codon-anticodon interactions during synthesis.
Genetic Code Properties
  • The codon table defines amino acids via triplet codons.
    • Degeneracy of the genetic code allows for redundancy, often preserving function despite mutations.
Molecular Techniques in Biology
  • PCR: Amplification of DNA through thermal cycling.
  • qRT-PCR: Quantification of RNA for diagnostic purposes.
  • CRISPR: Advanced technique for specific DNA and RNA detection, demonstrating high specificity.

FINAL NOTES

  • Emphasis on understanding molecular mechanisms serves to illuminate genetic processes fundamental to life and evolution.
    • Encourage seeking deeper understanding woven with faith and inquiry into the creator of these systems.