Final answer:
The correct answer is option a. The rich region's primary function in the oriC region of the E. coli chromosome is to initiate DNA replication by providing binding sites for initiator proteins and enzymes to start unwinding the DNA.
Step-by-step explanation:
The primary function of the rich region within the oriC region of the E. coli chromosome is a) DNA replication initiation. This region is approximately 245 base pairs long and is characterized by its high adenine-thymine (AT) content.
The AT-rich region allows for the binding of initiator proteins which, in conjunction with enzymes such as helicase, facilitates the unwinding of the DNA strand. This is an essential first step in creating replication forks where the DNA polymerase can then attach and begin the process of synthesizing a new strand of DNA.
The replication process in prokaryotes like E. coli starts at the single origin of replication, and extends bidirectionally, ensuring the entire circular chromosome is copied efficiently.