Biol+3301+-+12.+Molecular+Structure+of+DNA+and+RNA

Chapter 9 Molecular Structure of DNA and RNA

  1. Characteristics of the Genetic Material

    • Must possess information, transmission, replication, and variation.

  2. Experimental Evidence for DNA as the Genetic Material

    • a. Griffith and Transformation: Demonstrated transformation between pathogenic and non-pathogenic strains of bacteria.

    • b. Avery, MacLeod, and McCarty: Identified DNA as the transforming principle, proving it's the carrier of genetic information.

    • c. Hershey Chase Blender Experiment: Used radiolabeled phages to confirm that DNA, not protein, carries genetic information.

  3. Structure of DNA

    • a. Structure of Nucleotides: Composed of a phosphate group, sugar (deoxyribose in DNA), and nitrogenous bases.

    • b. Features of a DNA Strand and Double Helix: DNA is a double helix with antiparallel strands held together by hydrogen bonds.

    • c. Solving the Structure of DNA: Contributions from Franklin, Wilkins, Watson, and Crick led to the discovery of the double helix model.

    • d. Major vs. Minor Grooves: The structure allows protein binding and interaction, crucial for gene regulation.

  4. RNA Structure

    • a. Features of RNA: Composed of ribose sugar, single-stranded, and includes Uracil instead of Thymine.

    • b. RNA Secondary Structures: Can form structures such as hairpins and loops, critical for function.

Chapter 11. DNA Replication

  1. General Concepts in Replicating DNA Strands: Involves initiation, elongation, and termination.

  2. Semiconservative Mode of DNA Replication: Each new DNA molecule consists of one old and one new strand.

    • a. Meselson and Stahl Experiment: Used heavy and light nitrogen isotopes to demonstrate semiconservative replication.

  3. Bacterial DNA Replication: Includes origin of replication, DNA synthesis directionality (5’-3’), and the replisome components (helicase, gyrase, primase, polymerase).

    • d. Characteristics of DNA Polymerase: Enzymes that synthesize new DNA strands.

    • e. Leading vs. Lagging Strand: Leading strand synthesized continuously, lagging strand with Okazaki fragments, joined by ligase.

  4. Eukaryotic DNA Replication: More complex, includes telomeres and telomerase at chromosome ends.

Chapter 12 Gene Transcription and RNA Modification

  1. What is a gene? A sequence of DNA that encodes a functional product, usually a protein.

  2. General Concepts and Principles: Involves interactions between DNA and proteins.

    • a. DNA-Protein Interactions: Central to the regulation of transcription.

  3. Transcription in Bacteria: Involves stages: initiation, elongation, and termination; driven by RNA polymerase holoenzyme.

  4. Transcription in Eukaryotes: More complex regulatory elements compared to prokaryotes, including enhancers and silencers.

  5. RNA Modifications: Involves splicing out introns and connecting exons for functional mRNA.

Chapter 13. Translation of mRNA

  1. The Genetic Code: Dictates how nucleotide sequences translate into amino acids.

  2. Protein Structure: Characteristics include polypeptide directionality and properties of amino acids.

  3. Solving the Genetic Code: Pioneering experiments established codon-amino acid relationships.

  4. Transfer RNA (tRNA): Adapts between codons and amino acids, facilitated by aminoacyl tRNA synthetase.

  5. The Bacterial Ribosome: Involves three subunits and three functional sites (A, P, E) for translation stages.

Chapter 14. Gene Regulation in Bacteria

  1. General Concepts of Gene Regulation: From transcription initiation to protein modifications.

  2. Inducible and Repressible Gene Regulation: Involves various regulatory proteins and mechanisms.

  3. The lac Operon: An example of both negative and positive regulation depending on glucose availability.

Chapter 15. Gene Regulation in Eukaryotes

  1. General Concepts of Gene Regulation: Similar pathways exist with added complexity in eukaryotes.

  2. Transcription Factors: Key role in regulation, with elements like activators and repressors.

  3. Chromatin Remodeling: Important for accessibility of DNA for transcription; involves histone modifications

Histone acetylation and deacetylation are crucial modifications that affect gene regulation in eukaryotes.

  • Histone Acetylation: The addition of acetyl groups to histone proteins generally leads to a more open chromatin structure, enhancing the accessibility of DNA for transcription. This process is typically associated with gene activation, as it allows transcription factors and RNA polymerase to access the DNA more easily.

  • Histone Deacetylation: The removal of acetyl groups from histones causes the chromatin to become more compact, which can lead to the repression of gene expression. This process is associated with transcriptional silencing, as it makes the DNA less accessible for transcription machinery.

In summary, histone acetylation generally promotes transcriptional activity, while deacetylation is associated with transcriptional repression.

Allolactose is an isomer of lactose and serves as an important molecular signal in the regulation of the lac operon in bacteria. It acts as an inducer that binds to the repressor protein, preventing it from inhibiting the transcription of genes involved in lactose metabolism. This allows the genes for enzymes that digest lactose to be expressed when lactose is available in the environment.