| 1. | Thymine | 2. | Uracil |
| 3. | Adenine | 4. | Guanine |
| 1. | The two strands of polynucleotides are antiparallel i.e., run in the opposite direction. |
| 2. | The backbone is formed by the sugar-phosphate-sugar chain. |
| 3. | The nitrogen bases are projected more or less perpendicular to this backbone but face inside. |
| 4. | A and G of one strand compulsorily base pairs with C and T, respectively, on the other strand. |
In the DNA double helix:
| I: | At each step of ascent, the strand turns 34º. |
| II: | The rise per base pair would be 0.36 nm. |
| 1. | Only I is correct |
| 2. | Only II is correct |
| 3. | Both I and II are correct |
| 4. | Both I and II are incorrect |