What is the significance of DNA strands being complementary for replication?

• A. Each strand acts as a template for building a new strand in replication
• B. They cannot replicate
• C. They separate and stay separate
• D. They degrade into nucleotides

Answer: (A)

Complementarity is what makes DNA copying possible: the sequence on an existing strand precisely determines which nucleotides must be added to form the new strand. During replication, enzymes read the template strand and synthesize a new strand by pairing each exposed base with its partner (A with T, G with C). This pairing rule ensures that each new double helix contains one old strand and one newly made strand, a pattern called semi-conservative replication. Without complementary pairing, there would be no reliable guide for which nucleotides to insert, so accurate copying of the genetic information would not be possible. The system’s fidelity is further supported by proofreading that checks base pairing and corrects mistakes, preserving the genome.