Simulation · Biology · Class 12
Build a DNA double helix
From the lesson The double helix and central dogma in Molecular Basis of Inheritance. Change the values and watch what happens.
Build a DNA double helixBiology · Class 12
The idea behind it
NCERT § "The DNA"
- X-ray diffraction data from Maurice Wilkins and Rosalind Franklin, together with base-pairing, led James Watson and Francis Crick to propose the double-helix model in 1953.
- Erwin Chargaff had shown that in double-stranded DNA the amounts of A and T are equal, and so are G and C, which fits with complementary pairing.
- The two chains run antiparallel: one is 5′→3′ and the other 3′→5′. The sugar-phosphate backbones lie outside and the bases stack inside.
- A pairs with T through two hydrogen bonds; G pairs with C through three. A purine always faces a pyrimidine, keeping the distance between the two strands uniform.
- The chains coil in a right-handed manner. Each turn of the helix is 3.4 nm long (the pitch) and holds roughly 10 bp, so neighbouring base pairs are about 0.34 nm apart.
- Stacking of one base-pair plane over the next adds stability to the helix on top of the hydrogen bonds.
- Francis Crick proposed the central dogma: information flows DNA → RNA → protein. In some viruses information flows in reverse, from RNA to DNA.