Synthetic Nucleotide Analogues

• 5-iodo-2-deoxyuridine: A synthetic analogue that mimics deoxyuridine, incorporating iodine.
• 6-azauridine: A nucleotide analogue that contains an azole instead of a carbon, which may influence nucleic acid functions.
• 6-mercaptopurine: A purine analogue, primarily used in cancer treatment, which interferes with DNA replication.
• Allopurinol: A medication that inhibits xanthine oxidase, thereby reducing uric acid production and used in treating gout.

DNA Chain Structure

• The structure features:
  • Nucleotide Backbone: Comprised of sugar (deoxyribose) and phosphate groups.
  • Orientation: Displays a 5' to 3' directionality, with 5' and 3' ends marked by a phosphate and a hydroxyl group respectively.
  • Base Pairing: Adenine with Thymine (A-T) and Guanine with Cytosine (G-C) through hydrogen bonds.

Features of the DNA Strand

• Minor Groove: The smaller of the two grooves in the DNA helix, less accessible to proteins.
• Major Groove: The larger groove, where most DNA-binding proteins interact with the DNA sequence.
• Double Helix Dimensions:
  • Diameter: 2 nm
  • Rise per Base Pair: 0.34 nm
  • Base Pairs per Turn: 10

DNA Structure and Stabilization

• Winding: The 5' to 3' orientation contributes to the antiparallel strands of DNA.
• Stability Forces include:
  • Hydrophobic Interactions
  • Electrostatic Interactions
• Denaturation and Renaturation: Processes where the double helix separates (denaturation) and reforms (renaturation).

DNA Conformations

• B Form: The standard conformational structure found commonly in living organisms, right-handed.
• A Form: A right-handed conformation observed in dehydrated samples or certain RNA duplexes.
• Z Form: A left-handed conformation that can occur within stretches of DNA, particularly in sequences with alternating purines and pyrimidines.

Chargaff's Rule

• The empirical rule states:
  • Number of Adenine (A) = Number of Thymine (T)
  • Number of Guanine (G) = Number of Cytosine (C)
• This pairing is crucial in maintaining the double helix structure and ensuring accurate DNA replication.

Forces Stabilizing Nucleic Acid Structures

• Denaturation and Renaturation: Describe the dynamics of DNA unwinding and reassembling.
• Hydrophobic Interactions: Nonpolar regions of nucleobases aggregate away from water, stabilizing the helical structure.
• Electrostatic Interactions: Backbone phosphates repel each other; this is mitigated by cations like Na+ that neutralize the charge.

Supramolecular DNA Structures

• Nucleosome Core: DNA wrapped around histone proteins forming the basic unit of chromatin, consisting of 147 base pairs around a histone core.
• Histone Functions: Histones are proteins around which DNA is coiled, playing a critical role in gene regulation and fitting the lengthy DNA into the nucleus.
• Higher Order Structures: Include packed nucleosome formations, spirals, and chromatin fibers.

RNA Types and Functions

• Types of RNA:
  • mRNA (Messenger RNA): Carries genetic information from DNA to ribosomes.
  • tRNA (Transfer RNA): Adapts specific amino acids to be added during protein synthesis; typically consists of 73-95 nucleotides and ends with a CCA triplet.
  • rRNA (Ribosomal RNA): Structural component of ribosomes, crucial in protein synthesis.
  • Small RNAs (snRNA, siRNA, miRNA): Various roles in gene regulation and mRNA processing.

Differences Between DNA and RNA

Conclusion

• These notes encompass the structural and functional aspects of nucleic acids, illustrating their complexity and essential roles in biological systems. The interplay between DNA and RNA is foundational in molecular biology, providing the framework for understanding genetic expression and inheritance.