NEET2006ZoologyMolecular Basis of InheritanceActual
One turn of the helix in a B-form DNA is approximately:
Options
- A2 ~nm
- B20 ~nm
- C0.34 ~nm
- D3.4 ~nm
Correct answer
D. 3.4 ~nm
Step-by-step solution
B-DNA is a helical structure with a diameter of 20 Å and the distance between the two base pairs is 3.4 Å . There are 10 base pairs in each turn; hence, one turn of the helix (pitch of each helix) is approximately 34 Å or 3.4 ~nm (10=1.0 ~nm ) . Related Theory There are three different DNA types: (i) A-DNA: It is a right-handed double helix similar to the B-DNA form. Dehydrated DNA takes an A form that protects the DNA during extreme condition such as desiccation. (ii) B-DNA: The most common DNA conformation which