Learning objectivesUnderstand 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
Nucleic acid functionsDNA –genetic information storehouseRNA 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).
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
Structural features of the DNA(secondary structure)Double helix; 2 topographic features – major groove and minor grooveTwo strands antiparallelIn aqueous environment phosphate-sugar backbone outside of the helix; purine and pyrimidine rings inside the structureStrand stabilized by : H-bonds between complement bases Van der Waals and Hydrophobic interactions between stacked bases
Conformational varieties of the secondarystructure A B Z
Conformational varieties of the secondary structureB-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
A-DNA Dehydrated form of B-DNA Right handed helix 11 base pairs/helix Diameter = 26 A
Z-DNA Found in short stretches of native DNA and synthetic DNA Left handed helix 12 base pairs/helix Diameter = 18 A
At normal temp Increased tem, DNA denatures Sample becomes more turbid More light is absorbed
Tertiary structure of the DNACircular (relaxed) – in E.coli; simian virus 40; bacteriophage; certain animal speciesSupercoiled 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 DNAQuadruplex DNA – four stranded; in protozoan DNA; occur in G-rich regions; regulating and stabilizing telomeres and regulation of gene expression
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