Final answer:
DNA ligase is the enzyme most likely to be mutated when the joining of Okazaki fragments is impaired. It seals the nicks in the sugar-phosphate backbone of DNA, ensuring the continuity of the lagging strand. No enzyme currently exists that can eliminate bidirectional replication at the replication fork.
Step-by-step explanation:
The enzyme most likely to be mutated if the joining of Okazaki fragments is impaired in a cell strain is DNA ligase. This enzyme plays a critical role in sealing nicks between Okazaki fragments, completing the synthesis of the lagging strand during DNA replication. Without functional DNA ligase, the backbone of the DNA strand remains discontinuous, leading to replication defects.
Regarding the replication process, it is the leading strand that is synthesized in the direction toward the opening of the replication fork. In contrast, the lagging strand is synthesized in a direction away from the replication fork in short segments known as Okazaki fragments. For replication to be bidirectional, both the leading and lagging strands are synthesized simultaneously in opposite directions.Should an enzyme be developed that would eliminate the necessity for bidirectional replication at the replication fork, it would theoretically need to be able to synthesize both strands continuously in the same direction, something no current enzyme is known to do.