Final answer:
DNA synthesis occurs in the 5' to 3' direction because of the enzymatic properties of DNA polymerase, which can only add nucleotides to the 3' end of a DNA strand, leading to a synthesis direction that matches the leading strand's orientation and necessitates the creation of Okazaki fragments on the lagging strand.
Step-by-step explanation:
DNA synthesis occurs in the 5' to 3' direction because this is the only direction in which DNA polymerase can add nucleotides. To understand why let's look at the process of DNA replication. When DNA replicates, it unwinds and separates into two strands. Each strand serves as a template for a new strand. The enzyme DNA polymerase adds new nucleotides to a growing DNA strand, but it can only add them to the 3' end of the strand, which results in synthesis in the 5' to 3' direction.
For the strand that is oriented 3' to 5', replication can proceed smoothly, and this becomes the leading strand. However, the other original strand is oriented 5' to 3'. Because DNA polymerase cannot add nucleotides in that direction, this second strand, known as the lagging strand, is synthesized discontinuously in short fragments called Okazaki fragments. These are later joined together to form a continuous strand.
So, DNA synthesis occurs only in the 5' to 3' direction because that's how DNA polymerase functions. It is not because synthesis on the lagging strand occurs in the 3' to 5' direction, not because synthesis was chosen arbitrarily by evolution, not because 3' to 5' synthesis is biochemically impossible, and not because bond energy for error correction is always available (though it is provided by incoming nucleotides).