In the DNA molecule, that is formed by two strands of nucleotides, makes sense that each nucleotide is strongly bond to one another while the strands have weaker bonds, for one particular reason.
The double-stranded nature of the DNA is a key element in its correct functioning. <u>When the DNA needs to be "unzipped" for certain processes such as replication and transcription, the weak hydrogen bonds that connect the two strands are broken</u>. If the bonds between the strands were stronger, much more energy would be needed to perform the processes mentioned before, and that wouldn't be beneficial for the cells.
