That's a great question! Endonucleases don't actually cut DNA "between" the 5' and 3' ends. They cut within the DNA strand itself, and their activity is determined by the sequence of bases they recognize. Here's why:

* DNA Structure: DNA is a double helix composed of two antiparallel strands. One strand runs 5' to 3', and the other runs 3' to 5'.

* Endonucleases' Targets: Endonucleases are enzymes that break the phosphodiester bonds within a DNA strand. They have specific recognition sites, which are short sequences of bases.

* Specificity of Cutting: An endonuclease will only cut at its recognition site, regardless of the overall 5' to 3' directionality of the DNA strand.

Here's a simplified example:

Imagine an endonuclease recognizes the sequence "GAATTC." It will cut within this sequence, regardless of whether the strand it's acting on is the 5' to 3' strand or the 3' to 5' strand.

In summary: Endonucleases don't cut "between" the 5' and 3' ends of the DNA molecule. They cut *within* the strand at specific sequences they recognize. Their action is dictated by the base sequence and not the directionality of the DNA strand.