Final answer:
Complementary base pairing allows parent DNA strands to serve as templates for making new DNA strands during replication. Helicase unwinds the DNA, and semi-conservative replication results in new DNA molecules that each contain one parental strand and one new strand.
Step-by-step explanation:
Complementary base pairing allows for parental strands to act as templates for the synthesis of new DNA strands. During replication, the parental strands of DNA unwind at the origin of replication. The enzyme helicase facilitates this unwinding by separating the double-stranded DNA. The fact that only certain types of bases can pair together—adenine (A) with thymine (T) and guanine (G) with cytosine (C)—ensures accurate replication of the DNA sequence.
As DNA unwinds, two replication forks are formed that extend bidirectionally. Single-strand binding proteins coat the strands to prevent them from reannealing, while topoisomerase works ahead of the replication forks to relieve stress on the DNA molecule caused by unwinding. On each template strand, a complementary new strand is synthesized; one is built continuously, known as the leading strand, and the other is built in short segments, known as Okazaki fragments, composing the lagging strand.
The type of replication occurring in this process is semi-conservative. This means that each new DNA molecule consists of one parental strand and one newly synthesized complementary daughter strand. This semi-conservative nature was demonstrated by the Meselson and Stahl experiment and is fundamental to ensuring genetic fidelity during cell division.