Biomaterial Database

Thermodynamics of the B to Z transition in poly(m5dG-dC). 1986

J B Chaires, and J M Sturtevant

Differential scanning calorimetry, temperature-dependent absorbance, and circular dichroic spectroscopy were used to study the thermodynamics of the B-Z transition in poly(m5dG-dC). In sodium phosphate buffer (pH 7.0) containing 50 mM NaCl and 1.0 mM MgCl2, the reversible B-Z transition of the polymer is centered at 38.2 degrees C and is characterized by delta Hcal = 0.61 +/- 0.07 kcal/(mol X base pair) (1 cal = 4.184 J), delta HvH = 68 +/- 7 kcal/mol, and a cooperative unit of length 110 +/- 20 base pairs. A second transition centered at 53.6 degrees C is observed and represents a conformational change of poly(m5dG-dC) from the Z to an alternate left-handed form of unknown structure. This transition does not arise from aggregation to the Z form, or from the helix-coil transition. The left-handed helix-coil transition is observed at 120.9 +/- 0.3 degrees C and is characterized by delta Hcal = 9.1 +/- 1.0 kcal/(mol X base pair). These results indicate a substantial enthalpic contribution to the B-Z transition, in contrast to previous assertions that the process is entropically driven.

UI	MeSH Term	Description	Entries
D009690	Nucleic Acid Conformation	The spatial arrangement of the atoms of a nucleic acid or polynucleotide that results in its characteristic 3-dimensional shape.	DNA Conformation,RNA Conformation,Conformation, DNA,Conformation, Nucleic Acid,Conformation, RNA,Conformations, DNA,Conformations, Nucleic Acid,Conformations, RNA,DNA Conformations,Nucleic Acid Conformations,RNA Conformations
D011089	Polydeoxyribonucleotides	A group of 13 or more deoxyribonucleotides in which the phosphate residues of each deoxyribonucleotide act as bridges in forming diester linkages between the deoxyribose moieties.	Polydeoxyribonucleotide
D002151	Calorimetry	The measurement of the quantity of heat involved in various processes, such as chemical reactions, changes of state, and formations of solutions, or in the determination of the heat capacities of substances. The fundamental unit of measurement is the joule or the calorie (4.184 joules). (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)
D004247	DNA	A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine).	DNA, Double-Stranded,Deoxyribonucleic Acid,ds-DNA,DNA, Double Stranded,Double-Stranded DNA,ds DNA
D013816	Thermodynamics	A rigorously mathematical analysis of energy relationships (heat, work, temperature, and equilibrium). It describes systems whose states are determined by thermal parameters, such as temperature, in addition to mechanical and electromagnetic parameters. (From Hawley's Condensed Chemical Dictionary, 12th ed)	Thermodynamic