Final answer:
DNA strands are antiparallel to facilitate replication, with DNA polymerase only able to add nucleotides in the 5' to 3' direction. The leading strand is synthesized continuously, while the lagging strand requires Okazaki fragments. Parallel-stranded nucleic acids would necessitate a different replication mechanism.
Step-by-step explanation:
DNA Replication and Strand Orientation
DNA strands are inherently antiparallel in their structure; this means that one strand runs in a 5' to 3' direction while the complementary strand runs in a 3' to 5' direction. This is crucial for DNA replication because the enzyme responsible for synthesizing new DNA strands, DNA polymerase, can only add nucleotides in the 5' to 3' direction.
The way replication occurs is that one strand, known as the leading strand, is synthesized continuously in the direction of the replication fork. The other strand, called the lagging strand, must be synthesized in short stretches called Okazaki fragments because it runs in the opposite direction to that of the DNA polymerase's action. These fragments are then linked together to create a continuous strand. The necessity for antiparallel orientation stems from the enzyme's directional limitation and the requirement to maintain the integrity of the genetic code during replication.
If a hypothetical novel nucleic acid were to have parallel strands, this would imply a need for a different replication mechanism entirely, since the current biochemical processes that govern DNA replication on Earth are not compatible with parallel-stranded structures.