It is surmised that statistical disordering of deoxyoligonucleotide structures which take a Z conformation, depends on the length of the oligomer. Thus, the basis of the stabilization of Z-DNA by 3+ is its binding to only guanine nucleotides. On the other ZII chain, one ammonia molecule of the cobalt hexammine binds only to the anionic oxygens of the phosphate group of the guanine bases, leading to an "internal" binding mode. The nucleobase or 'base' imparts the variation in each nucleotide unit while the phosphate and sugar portions form the backbone structure of the DNA. In other words, it is a double stranded molecule that twists like a spiral staircase. The backbone is highly negatively charged as a result of the. On one ZII chain, two ammonia molecules of the cobalt hexammine bind to the N7 nitrogen and 06 oxygen atoms of the guanine bases and a third ammonia to the phosphate anionic oxygen atom of the preceding pyrimidine base, resulting in an "external" binding mode. The sugar and phosphate groups in the helix therefore make up the phosphate backbone of DNA. creating a strong backbone for the molecule of alternating sugar and. The cobalt hexammine binds to two ZII-chains of symmetrically related molecules. The structure of DNA molecule is vital for understanding the replication and. The structure was found to have one strand in the ZI-conformation and the other in the ZII-conformation. Restrainted least-squares refinement led to an R-factor of 25.5% for 506 observed reflections above the two-sigma level. The asymmetric unit is a dimer (pPyr-pPur)2 with each base pair 60% of the time a C-G and 40% of the time a T-A. The decamers stack on top of each other and form a quasi-continuous helix. The molecules have the helix axis coincident with the crystal c-axis. From the abbreviation of DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid) we can get the name of sugar group. The repeated unit of sugar and phosphate group is the backbone of DNA. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules (A with T and C with G), with hydrogen bonds to make double-stranded DNA. Nucleotides are composed of sugar group, phosphate group and a nitrogen base. The structure of DNA is a double helix Hydrogen strand. The complex between cobalt hexammine and decadeoxyoligomer d(CGTACGTACG) crystallizes into the space group P65 with unit cell constants a = b = 17.93A, and c = 43.41A. In 1953, James Watson and Francis Crick discovered the DNA structure.
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