| Popis: |
In this paper, the side-by-side model of DNA proposed by Premilat and Albiser is investigated. The axial repeat of the model is equal to the c-axis repeat in the observed B-DNA unit cell in fibres. However, the model does not pack into the unit cell as efficiently as the B-DNA double helix does, nor is it as successful as the double helix in predicting the observed Bragg amplitudes. When the azimuthal orientations and the relative axial displacements of the two molecules in the unit cell are allowed to take general values, the best crystallographic R factor for the side-by-side model is 43.43% compared with 34.33% for the double helix. If constraints consistent with the accepted B-DNA space group, P2(1)2(1)2(1), are applied, the best R factors are 45.53% for the side-by-side model and 34.51% for the double helix. Therefore, the side-by-side model can be rejected as a possible conformation for B-DNA in crystalline fibres. |
