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  4. One turn of the helix in a B-form DNA is approximately

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Q. One turn of the helix in a B-form DNA is approximately

Bihar CECEBihar CECE 2013

Solution:

B-DNA is helical structure with 20A diameter and the distance between the two base pairs is 3.4 $ \overset{o}{\mathop{A}}\, $ and there are 10 base pairs in each turn or pitch (one round). Hence, one turn of the helix is approximately 34 $ \overset{o}{\mathop{A}}\, $ or 3.4 nm (10 $ \overset{o}{\mathop{A}}\, $ = 1.0 nm)