Here's a breakdown of the process:
1. Base Pairing: The two strands of DNA align in an antiparallel orientation (running in opposite directions). Adenine (A) on one strand pairs with Thymine (T) on the other strand, and Guanine (G) pairs with Cytosine (C). This base pairing is dictated by hydrogen bonding between the bases.
2. Stacking Interactions: The paired bases then stack on top of each other, forming a structure like a twisted ladder. This stacking arrangement provides stability and allows for the formation of the double helix.
3. Helix Formation: The two strands, now paired and stacked, twist around each other to form the double helix. The double helix is stabilized by hydrophobic interactions between the bases and by interactions with the sugar-phosphate backbone.
Therefore, the first step in DNA double helix formation is the pairing of complementary nitrogenous bases.
