Explanation:
Watson & Crick discovered that DNA is composed of two (2) strands of DNA running antiparallel to each other. One strand is oriented in the 5’ -> 3’ direction while the other is oriented in the 3’ -> 5’ direction. The nitrogenous bases of the strands are found in between the two-strand backbones and they form hydrogen bonding with each other. Specifically, pyrimidines (Cytosine and Thymine) pair with purine (Adenine and Guanine).
The space between the strands is even throughout like a ladder with rungs of equal lengths. However during the twisting on the DNA helix, there are major grooves and minor grooves that form along the helix because of the nature of how the nitrogenous bases are attached to their respective strand. They do not project from their strands at 90 degrees.
Learn More:
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