List the salient features of double helix structure of DNA.

1.	List the salient features of double helix structure of DNA.
Answer» The salient features of double helix structure of DNA are : (i) The DNA is made up of two polynucleotide chains, where the backbone is made up of sugar and phosphate groups and the nitrogenous base projecting to the centre. (ii) The diameter of the Strand is always equal due to pairing of purine and pyramidine i.e. , adenine is complementary to thymine While guanine is complementary to cytosine. (iii) The stability of the DNA structure is due to strong bond between negetively charged nucleic acid and positively charged basic histone protein, along with hydrogen bonds between the base pairs of two strands.

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(i) Arrange the following compounds in an increasing order of basic strength : `C_(6)H_(5)NH_(2), C_(6)H_(5)N(CN_(3))_(2), (C_(2)H_(5))_(2)NH and CH_(3)NH_(2)` (ii) Arrange the following compounds in a decreasing order of `pK_(b)` values: `C_(2)H_(5)NH_(2), C_(6)H_(5)NHCH_(3), (C_(2)H_(5))_(2) NH and C_(6)H_(5)NH_(2)`
Rerrange the following in an increasing order of their basic strengths: `C_(6)H_(5)NH_(2),C_(6)H_(5)N(CH_(3))_(2),(C_(6)H_(5))_(2)` NH and `CH_(3)NH_(2)`.
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List the salient features of double helix structure of DNA.

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