Context: Due to the chemical composition of the pentose residues of the bases, DNA strands have directionality. One end of a DNA polymer contains an exposed hydroxyl group on the deoxyribose; this is known as the 3' end of the molecule. The other end contains an exposed phosphate group; this is the 5' end. The two strands of a double-helix run in opposite directions. Nucleic acid synthesis, including DNA replication and transcription occurs in the 5'→3' direction, because new nucleotides are added via a dehydration reaction that uses the exposed 3' hydroxyl as a nucleophile.:27.2

Question: What causes the directionality of DNA strands?
Answer: the chemical composition of the pentose residues of the bases

Question: What is known as the 3' end?
Answer: an exposed hydroxyl group on the deoxyribose

Question: What is known as the 5' end?
Answer: an exposed phosphate group

Question: What type of synthesis occurs in the 5'→3' direction?
Answer: Nucleic acid synthesis

Question: Why does DNA replication and transcription occur in the 5'→3' direction?
Answer: because new nucleotides are added via a dehydration reaction that uses the exposed 3' hydroxyl as a nucleophile