Complex sentence: These nucleotides possess the non-canon sugar dideoxyribose, which lacks 3' hydroxyl group (which accepts the phosphate) and therefore cannot bond with the next base, terminating the chain, as DNA polymerases cannot distinguish between it and a regular deoxyribonucleotide.
Split into simpler sentences: These nucleotides possess the non-canonical sugar dideoxyribose, which lacks 3' hydroxyl group (which accepts the phosphate). It therefore cannot bond with the next base and terminates the chain, as DNA polymerases cannot distinguish between it and a regular deoxyribonucleotide.