Final answer:
The origin of replication is composed of the bases A and T because of the specific nucleotide sequence at the origin of replication. A and T base pairs have two hydrogen bonds, making them easier to separate. This allows the replication machinery to initiate DNA unwinding and replication at the origin of replication.
Step-by-step explanation:
The origin of replication is composed of the bases A and T because of the specific nucleotide sequence at the origin of replication. The origin of replication is a region where replication begins, and it is recognized by certain proteins.
In E. coli, which is a prokaryote, the origin of replication is approximately 245 base pairs long and is rich in AT sequences. A and T base pairs have two hydrogen bonds, which require less energy to break compared to the three hydrogen bonds of G and C base pairs.
Due to these properties, A and T base pairs are more easily separated, allowing the replication machinery to initiate DNA unwinding and replication at the origin of replication.