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Nucleic acid structures

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  • 1. Nucleic Acid Structures
  • 2. Learning objectives Understand the molecular structure of DNA. Understand the molecular structure of RNA. Understand the relationships between purines, pyrimidines, nucleosides, nucleotides, and nucleic acids. Understand the structural differences between DNA and RNA
  • 3. Nucleic acid functions DNA –genetic information storehouse RNA  message between the genome and the ribosome for the building of proteins (messenger RNA, or mRNA),  act as the catalytic moiety in a RNA-protein enzyme complex (rRNA)  serve as the translator between mRNA sequence and protein sequence (tRNA) RNA and DNA- recent discovery catalyze some reactions without protein involvement (ribozymes or deoxyribozymes).
  • 4. 9000 year old “Kennewick man” skull discovered along the banks ofthe Columbia River in Washington state believed to have originatedfrom Southeast Asia, Japan or Polynesia DNA from archeological samples Compared to modern DNA Evidence of DNA stability
  • 5. SUGAR + BASE = NUCLEOSIDE
  • 6. Nucleotide – monomeric unit in nucleic acid
  • 7. Deoxythymidine 5’-monophosphateDeoxyadenosine 5’-monophosphateDeoxycytidine 5’-monophosphateDeoxyguanosine 5’-monophosphate
  • 8. N-glycosidic bond3’,5’-phosphodiester bond
  • 9. C1’-N1= Pyr C1’-N9 = Pur
  • 10. Structural features of the DNA(secondary structure) Double helix; 2 topographic features – major groove and minor groove Two strands antiparallel In aqueous environment phosphate-sugar backbone outside of the helix; purine and pyrimidine rings inside the structure Strand stabilized by : H-bonds between complement bases Van der Waals and Hydrophobic interactions between stacked bases
  • 11. Conformational varieties of the secondarystructure A B Z
  • 12. Conformational varieties of the secondary structure B-DNA – crystallized from water; water retained in the inner structure; predominant form under physiological conditions 10 base pairs/turn of helix Right handed Distance bet base pairs 0.34 nm Diameter – 2.0 nm or 20 A
  • 13.  A-DNA Dehydrated form of B-DNA Right handed helix 11 base pairs/helix Diameter = 26 A
  • 14.  Z-DNA  Found in short stretches of native DNA and synthetic DNA  Left handed helix  12 base pairs/helix  Diameter = 18 A
  • 15. 85-90 degrees asthe meltingtemperature
  • 16. Tm = midpoint of each curve
  • 17. At normal temp Increased tem, DNA denatures Sample becomes more turbid More light is absorbed
  • 18. Tertiary structure of the DNA Circular (relaxed) – in E.coli; simian virus 40; bacteriophage; certain animal species Supercoiled DNA – extra twisting in the linear duplex; allows DNA to be more compact in the cell; regulatory role in replication  Topoisomerase – change topology of the DNA Quadruplex DNA – four stranded; in protozoan DNA; occur in G-rich regions; regulating and stabilizing telomeres and regulation of gene expression