Complex sentence: Ribonucleotide reductase catalyzes the formation of deoxyribonucleotides from ribonucleotides, thus, DNA replication is inhibited and cells cannot replicate.
Split into simpler sentences: Ribonucleotide reductase catalyzes the formation of deoxyribonucleotides from ribonucleotides. Thus, DNA replication is inhibited and cells cannot replicate.