Base pairs with a propeller-twist have optimum base stacking .
Propeller Twist in the base-pairs is needed to makes stacking into a dinucleotide step more stiff in comparison to the plane base pairs. It act for providing a stereochemical locking effect which can make staircase for highly propeller twisted base pairs more rigid.
Twists are important in DNA double helix structure as it helps to avoid crashing into each other , so the structure is twisted and spiral in structure . This extra twist at the end is the reason for the helical shape. Distance between two consecutive base pairs is 0.34 nm and one complete turn of the double helix has 10 base pairs which means that it is 3.4 nm/ 34 A˚ long.
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