Natalia Tretyakova, College of Pharmacy, U. of Minnesota
Richard Lavery, Institut de Biologie Physico-Chimique, Paris
Overview of DNA Structure
DNA is a double helix structure storing genetic code through a sequence of bases.
Human genome consists of approximately 3.3 billion base pairs and around 25,000 genes.
DNA Size Scale
Chemical bond: 1 Å (10^-10 m)
Amino acid: 10 Å (10^-9 m)
Globular protein: 100 Å (10^-8 m)
Virus: 1000 Å (10^-7 m)
Cell nucleus: 1 µm (10^-6 m)
Bacterial cell: 5 µm (10^-5 m)
Chromosome DNA: 10 cm (10^-1 m)
Nucleotides and DNA Structure
Nucleotides form DNA through phosphodiester bonds.
DNA strands have directionality (5' to 3').
DNA backbone is negatively charged due to phosphate groups.
Base Families
Purine: Adenine (A), Guanine (G)
Pyrimidine: Thymine (T), Cytosine (C), Uracil (U, in RNA)
Purines have a two-ring structure, pyrimidines have a single-ring structure.
Nucleosides and Nucleotides
Nucleoside: A base linked to a sugar (ribose or deoxyribose).
Nucleotide: Nucleoside with one or more phosphate groups.
DNA and RNA Differences
DNA: Contains deoxyribose, bases A, T, G, C
RNA: Contains ribose, bases A, U, G, C
DNA Helix Structure
B-DNA is the common form, with right-handed helix, antiparallel strands, and base pairs inside the helix.
Helix features major and minor grooves, important for protein interactions.
Base Pairing: A-T and G-C with hydrogen bonding.
DNA stability is maintained by hydrogen bonds, stacking interactions, and electrostatic forces.
Alternative DNA Forms
A-DNA: Dehydrated form, right-handed, more compact.
Z-DNA: Left-handed, occurs in high salt conditions or specific sequences.
Historical Context of DNA
1865: Genes concept by Gregor Mendel.
1869: "Nuclein" discovery by Johann Friedrich Miescher.
1953: Watson and Crick propose the DNA double helix structure based on X-ray diffraction data from Rosalind Franklin and Maurice Wilkins.
DNA Function and Biological Importance
DNA replication, transcription, and translation are central to the central dogma of molecular biology.
DNA hybridization involves the formation of double-stranded DNA from complementary strands and is crucial for biological processes and laboratory techniques.
DNA Technology and Applications
Peptide Nucleic Acids (PNAs) are synthetic polymers that mimic DNA/RNA but with a peptide-like backbone.
Used for high-specificity hybridization and resistant to enzymatic degradation.
Conclusion
DNA's structure and functionality are central to understanding biological processes and genetic information storage and transfer.