(D)RNA = (Deoxy)ribose nucleic acid

It has 3 components:

  1. a nitrogenous base : purine (A,G) or pyrimidine (T,C) is linked at position 1 on a pentose sugar.
  2. a sugar : DNA has 2'-deoxyribose where as RNA has ribose (OH group at potition 2 on pentose ring).
  3. and a phosphate : The sugar can be linked by its 5' position to a phosphate group or 3' position to next nucleic acid's phosphate. (direction : 5' --> 3')

*DNA contains A,G, C, T, while RNA contains A, G, C, U.

DNA is a double heliex : Base pairing (A=T;GC), Complementary, Antiparallel

A helix is said to be right-handed if the turns runs clockwise along the helical axis.

The sugar-phosphate backbone is on the outside and carries negative charges on the phosphate groups. When DNA is in solution in vitro, the charges are neutralized by the binding of metal ions, typically by Na+.

Each base pair is rotated ~36° around the axis of the helix relative to the next base pair. So ~10 base pairs make a complete turn of 360°. The minor groove of DNA is 12Å across. The major groove of DNA is 22Å across. These features represent the accepted model for what is known as the B-form of DNA. If it has more base pairs per turn it is said to be overwound; if it has fewer base pairs per turn it is underwound.


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