How to draw DNA

The DNA has twisted ladder or double helical structure. According to Watson and Crick DNA molecule consists of two polynucleotide chains wrapped helically around each other, with the sugar- phosphate chain on the outside forming ribbon-like backbone of double helix. Purines and pyrimidines on the inside of the helix projecting between two sugar phosphate backbones as transverse bars. The two polynucleotide strands are held together by hydrogen bonds between specific pairs of Purines and Pyrimidines.  Now let's see how to draw DNA accurately.

 1.Draw two vertical parallel lines as shown with pencil.

2. Draw a twisted wave touching two lines on either sides.

3. Draw another wavy curve as shown. Start the second curve  a bit near the first curve to get proper grooves of DNA.

4. Make ribbon shape on  the strands as shown. Make sure the curves you draw end at correct points as shown.

5.Draw ribbon shape on other strands too, let the two strands cross each other for now.

6. Erase the appropriate lines at crossing point such that one strand goes up at one point and goes down at next point.

 Draw transverse bars four per turn at equal distance as shown.

Label the minor goove and major grooves and other details as shown.

Continued- The hydrogen bonds between purines and pyrimidines aere such that adenine can bond only to thymine by two hydrogen bonds, and guanine can bond only to cytosine by three hydrogen bonds. The two strands urn anti-prallely that is, one strand has phosphodiester linkage in 3' to 5' direction, while other strand has phosphodiester linkage in reverse 5' to 3' direction. Both, strands remain separated by 20 Armstrong units. The coiling of double helix is right handed and a complete turn occurs every 34 Armstrongs. The helix has two external grooves, a deep wide one called Major groove and a shallow narrow one called minor groove.