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Lecture11_NABPty2012 (1)

Nucleic acids require counterions such as mg2

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Unformatted text preview: or other proteins to balance this charge. OPO M+ CH 2 O N O O M+ OPO CH 2 O O N 3’ O-PO32 M+ OH HO-CH2 H-C=O O 5’ HO-CH2 H-C-OH The sugars are always in the β -furanose (cyclic) form N O H-C-OH OH H-C-OH OH β -furanose (cyclic) form CH2OH ribose in its aldehyde form O OPO OH CH2 O 5’ O O 4’ N OH OPO N endo O 1’ 3’ CH2 C-2’ exo N O O OPO OH CH2 O The ring can adopt various puckered conformations in which C-2’ and C-3’are in either exo or endo positions relative to the base and C-5’. O N 3’ O-PO32 OH NH2 The nucleotide base can rotate with respect to the sugar C N C HC C N HOCH2 N N CH HC N N HOCH2 O OH The bases can adopt either syn or anti conformations, but anti conformations are preferred. NH2 syn-Adenosine anti-Adenosine NH2 N O HOCH2 OH CH HC C CH HC N HOCH2 O OH syn-Cytosine N OH NH2 C C O OH OH C C OH C N N O OH anti-Cytosine C O N CH The pattern of X-ray diffraction by DNA fibers reveals a helical structure with steps of 3.4 and 34 Å This This x-ray diffraction by calf thymus DNA was measured by Franklin & Gosling in 1952. The X pattern is indicative of a helix with a pitch of 34 Å per turn. The strong spots at the top and bottom reveal internal s...
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