Final answer:
Dideoxynucleotides are crucial in DNA sequencing because their absence of a 3' hydroxyl group terminates DNA synthesis, allowing for the determination of DNA sequences in methods like Sanger sequencing.
Step-by-step explanation:
A dideoxynucleotide differs from a deoxynucleotide by lacking a 3' hydroxyl group (-OH) on the sugar molecule. This missing hydroxyl group is critical because it prevents further addition of nucleotides, thus terminating DNA synthesis when incorporated into a DNA strand. The significance of this difference is well illustrated in the Sanger method of DNA sequencing, where the incorporation of dideoxynucleotides leads to the creation of DNA fragments of various lengths that can be used to determine the sequence of the DNA strand.