Bioetanol Microalgas

molecular structure of nucleic acids.
a structure for deoxyribose nucleic acid.
we wish to suggest a structure for the salt of deoxyribonucleic acid. this structure has novel features wich are of considerable biological interest.
a structure for nucleic acid has already been proposed by pauling and corey. they kindly made their manuscript available to us in advance of publication. their modelconsists of three intertwined chains, with the phosphates near the fibre axis, and the bases on the outside. in our opinion, this structure is unsatisfactory for two reason: 1. we believe that the material which gives. the X-ray diagrams is the salt, not the free acid. without the acidic hydrogen atoms it is not clear what forces would hold the structure together, especially as the negativelycharged phosphates near the axis will repel each other. 2. some of the van der waals distances appear to be too small.
another three-chain structure has also been sugested by fraser ( in the press). in his model the phosphates are on the outside and the bases on the inside , linked together by hydrogen bonds. this structure as described is rather ill-defined, and for this reason we shall not commenton it.
we wish to put forward a radically different structure for the salt of deoxyribose nucleic acid. this structure has two helical chains each coiled round the same axis,(see diagram).we have made the usual chemical assumptions, namely, that each chains consists of phosphate di-ester groups joining b - d - deoxyribofuranose residues with 3', 5' linkages.
the two chains (but not their bases) are related by a dyad perpendicular to the fibra axis. both chains follow right-handed helices, but owing to the dyad the sequences of the atoms in the two chains run in opposite directions. each chains loosely resembles furberg's model No 1; that is, the bases are on the inside of the helix and the phosphates on the outside. the configuration of the sugar and the atoms near is the close tofurgberg's 'standard configuration', the sugar being roughly perpendicular to the attached base. there is a residue on each chain every 3.4 a. in the z-direction. we have assumed an angle of 36 grade between adjacent residues in the same chain, so that the structure repeats after 10 residues an each chain,that is, after 34 a.the distance of a phosphorus atom from the fibre axis is 10a. as thephosphates are on the outside, cations have easy access to them.
the structure is an open one, and its water contentis rather high.at lower water contents we would expect the bases to tilt so that the structure could become more compact.
the novel feature of teh structure is the manner in wich the two chains are held together by purine and pyrimidine bases. the planes of the bases are perpendicular tothe fibra axis. tehy are joined togethers in pairs, a single base from the other chain,so that the two lied side by side with identical z-co-ordinates.one of the pairmust be a purine and the other a pyrimidine for bonding to occur. the hydrogen bonds are made as follows: purine position 1. to pyrimidine position 1; purine position 6 to pyrimidinr position 6.
if it is assumed that the bases on lyoccur in the structure in the most plausible tautomeric forms (that is, with the keto rather than the enolconfigurations) it is found that only specific pairs of abse can bond together.these pairs are : adenine (purine) with thymine (pyrimidine), and guanine (purine) with cytosine (pyrimidine).
in others words, if an adenine forms one member must be thymine; similary for guanine and cytosine. thesquences of bases on a single chains does not appear to be restricted in any way. however, if only specifis pairs of bases can be formed, it follows taht if the squence of bases on one chain is given,then the squence on the other chains is automatocally determine.
it has been found experimentally that the ratio of the amounts of the adenine to thymine,and the ratio of guanine to cytosine, are...