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 of
the Columbia River in Washington state believed to have originated
from Southeast Asia, Japan or Polynesia
DNA from
archeological
samples
Compared to modern
DNA
Evidence of DNA
stability
15. 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
19. 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
20. A-DNA
Dehydrated form of B-DNA
Right handed helix
11 base pairs/helix
Diameter = 26 A
21. Z-DNA
Found in short stretches of native DNA
and synthetic DNA
Left handed helix
12 base pairs/helix
Diameter = 18 A
24. At normal temp Increased tem, DNA denatures
Sample becomes more turbid
More light is absorbed
25. 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